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Effect of repeated firing on color and translucency of different CAD/CAM lithium disilicate reinforced glass-ceramic materials
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Effect of repeated firing on color and translucency of different CAD/CAM lithium disilicate reinforced glass-ceramic materials
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Content
Effect of Repeated Firing on Color and Translucency of Different CAD/CAM Lithium
Disilicate Reinforced Glass-Ceramic Materials
by
Andrea Ramírez Goercke, DDS, MS
A Thesis Presented to the
FACULTY OF THE USC HERMAN OSTROW SCHOOL OF DENTISTRY
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirement for the Degree
MASTER OF SCIENCE
(BIOMATERIALS AND DIGITAL DENTISTRY)
December 2022
Copyright 2022 Andrea Paola Ramírez Goercke
ii
Dedication
I will like to dedicate my work to my parents, my sister, my nephew, my brother in
law, my future husband and my son. You are the engine and strenght behind everything
I do.
iii
Acknowledgements
First, I would like to thank God for all the blessings and opportunities he has put in
my way. He has been my strength in my weakest moments.
I would like to thank my parents, for always believing in me and encouraging me to
always be a better person. I am where I am today because of them. I could not have done
any of this without their love and support.
I would like to thank my sister, my brother-in-law, and my beloved nephew for all the
love and support and for always making me smile trough the hard times.
Special thanks to my fiancé, for being the strength and support when I tough, I could
not keep going, and for always backing up my crazy ideas and dreams even tough that
means that we have to be kilometer apart from each other.
With much appreciation, I acknowledge the members of the Committee for all their
efforts and for their time.
I would like to express my full and special gratitude to my supervisor Dr. Jin-Ho
Phark, for all the lessons he has given me, and for pushing me to be the best I can be.
Thank you for helping me with this work, and for giving me this opportunity, this research
could not have been possible without you and your hard work.
I would also like to thank Dr. Sillas Duarte for the opportunity he gave me to
participate in this program, and for his advice and constant updates with the current
literature.
My special appreciation and love to all the faculty that has been part of my formation
at USC. Each one of you have taught me invaluable lessons. Thank you for sharing your
knowledge with me and for allowing to learn from you.
Last, but not least thanks to the Advanced Operative residents, we have shared a
special adventure, and special thanks to my co-residents Nazanin and Sarah, who did not
iv
only become my friends, but they were also my family. Thank you, girls, we have been
through so much together, but we made it.
v
Table of Contents
DEDICATION .................................................................................................................. II
ACKNOWLEDGEMENTS ............................................................................................ III
LIST OF TABLES .......................................................................................................... IX
LIST OF FIGURES ....................................................................................................... XV
ABBREVIATIONS ..................................................................................................... XXI
ABSTRACT ............................................................................................................... XXII
1. INTRODUCTION .................................................................................................... 1
1.1 DIGITAL DENTISTRY .......................................................................................... 1
1.2 CAD-CAM MATERIALS .................................................................................... 3
1.2.1 Classification ................................................................................................ 3
1.2.2 Glass Ceramics ............................................................................................. 5
A. Feldsphatic Ceramics .................................................................................... 5
B. Lithium Disilicate ......................................................................................... 7
B.1. Background ............................................................................................... 7
B.2. Chemical Composition .............................................................................. 7
B.3. Products ..................................................................................................... 8
C. Zirconia Reinforced Lithium Silicate ......................................................... 11
1.2.3 Crystallization, Staining and Glazing ......................................................... 11
A. Two-stage Process ......................................................................................... 12
B. Three-stage Process ....................................................................................... 12
C. Staining and Glazing ...................................................................................... 12
1.3 OPTICAL CHANGES .......................................................................................... 13
1.3.1 Color Science and Translucency in Dentistry ............................................... 13
A. Color Systems ................................................................................................ 14
B. Measuring devices ......................................................................................... 16
B.1 Visual Method .......................................................................................... 16
B.2 Spectrophotometers .................................................................................. 17
B.3 Colorimeters ............................................................................................. 17
B.4 Digital Cameras ....................................................................................... 17
B.5 Intraoral Scanners .................................................................................... 17
1.4 COLOR AND TRANSLUCENCY RESEARCH ......................................................... 18
2. AIM ........................................................................................................................ 19
3. NULL HYPOTHESIS ............................................................................................ 19
3.1 COLOR CHANGE ..................................................................................................... 19
3.2 TRANSLUCENCY PARAMETER ................................................................................ 19
4. MATERIALS AND METHODS ........................................................................... 20
4.1 MATERIALS ............................................................................................................ 20
4.2 SPECIMEN PREPARATION ....................................................................................... 22
4.3 SPECIMEN FIRING .................................................................................................. 25
4.4 COLOR AND TRANSLUCENCY ANALYSIS ................................................................ 28
4.4.1 Color Analysis ............................................................................................... 30
vi
4.4.2 Translucency Analysis ................................................................................... 33
4.5 STATISTICAL ANALYSIS ......................................................................................... 34
5. RESULTS ............................................................................................................... 35
5.1 COLOR CHANGE ANALYSIS .................................................................................... 35
5.1.1 Overall Comparisons .................................................................................. 35
A. Overall comparison between different materials ........................................ 39
B. Overall comparison between different thicknesses ........................................ 41
C. Overall comparison between different firings ............................................... 42
5.1.2 IPS e.max CAD Comparisons .................................................................... 43
A. IPS e.max CAD Thickness ......................................................................... 43
B. IPS e.max CAD 0.5 mm Firings .................................................................... 44
C. IPS e.max CAD 1 mm Firings ....................................................................... 46
5.1.3 n!Ce Comparisons ...................................................................................... 48
A. N!Ce Thickness .......................................................................................... 48
B. N!Ce 0.5 mm Firings ..................................................................................... 49
C. N!Ce 1 mm Firings ........................................................................................ 50
5.1.4 Initial lisi Block Comparisons .................................................................... 52
A. Initial lisi Block Thickness ......................................................................... 52
B. Initial lisi Block 0.5 mm Firings .................................................................... 53
C. Initial lisi Block 1 mm Firings ....................................................................... 54
5.1.5 Amber Mill Comparisons ........................................................................... 55
A. Amber Mill Thickness ................................................................................ 55
B. Amber Mill 0.5 mm Firings ........................................................................... 56
C. Amber Mill 1 mm Firings .............................................................................. 58
5.2 CIE L*A*B* .......................................................................................................... 60
5.2.1 L* overall comparison ................................................................................... 60
B. L* overall comparison between different materials ................................... 62
C. Overall comparison between different thicknesses .................................... 64
D. Overall comparison between different firings ............................................ 65
5.2.2 IPS e.max CAD Comparisons .................................................................... 67
A. IPS e.max CAD Thickness ............................................................................ 67
B. IPS e.max CAD 0.5 mm Firings .................................................................... 68
C. IPS e.max CAD 1 mm Firings ....................................................................... 69
5.2.3 n!Ce Comparisons ...................................................................................... 70
A. N!Ce Thickness ............................................................................................. 70
B. N!Ce 0.5 mm Firings ..................................................................................... 71
C. N!Ce 1 mm Firings ........................................................................................ 72
5.2.4 Initial lisi Block Comparisons .................................................................... 74
A. Initial lisi Block Thickness ............................................................................ 74
B. Initial lisi Block 0.5 mm Firings .................................................................... 75
C. Initial lisi Block 1 mm Firings ....................................................................... 76
5.2.5 Amber Mill Comparisons ........................................................................... 77
A. Amber Mill Thickness ................................................................................... 77
B. Amber Mill 0.5 mm Firings ........................................................................... 77
C. Amber Mill 1 mm Firings .............................................................................. 79
5.3.1 a* overall comparison .................................................................................... 81
A. A* overall comparison between different materials ................................... 83
B. Overall comparison between different thicknesses .................................... 85
C. Overall comparison between different firings ............................................ 86
vii
5.3.2 IPS e.max CAD Comparisons .................................................................... 87
A. IPS e.max CAD Thickness ............................................................................ 87
B. IPS e.max CAD 0.5 mm Firings .................................................................... 88
C. IPS e.max CAD 1 mm Firings ....................................................................... 89
5.3.3 n!Ce Comparisons ...................................................................................... 91
A. N!Ce Thickness ............................................................................................. 91
B. N!Ce 0.5 mm Firings ..................................................................................... 92
C. N!Ce 1 mm Firings ........................................................................................ 93
5.3.4 Initial lisi Block Comparisons .................................................................... 95
A. Initial lisi Block Thickness ............................................................................ 95
B. Initial lisi Block 0.5 mm Firings .................................................................... 96
C. Initial lisi Block 1 mm Firings ....................................................................... 97
5.3.5 Amber Mill Comparisons ........................................................................... 99
A. Amber Mill Thickness ................................................................................... 99
B. Amber Mill 0.5 mm Firings ......................................................................... 100
C. Amber Mill 1 mm Firings ............................................................................ 101
5.4.1 b* overall comparison ................................................................................. 103
A. B* overall comparison between different materials ................................. 105
B. Overall comparison between different thicknesses .................................. 107
C. Overall comparison between different firings .......................................... 108
5.4.2 IPS e.max CAD Comparisons .................................................................. 109
A. IPS e.max CAD Thickness .......................................................................... 109
B. IPS e.max CAD 0.5 mm Firings .................................................................. 110
C. IPS e.max CAD 1 mm Firings ..................................................................... 111
5.4.3 n!Ce Comparisons .................................................................................... 113
A. N!Ce Thickness ........................................................................................... 113
B. N!Ce 0.5 mm Firings ................................................................................... 114
C. N!Ce 1 mm Firings ...................................................................................... 115
5.4.4 Initial lisi Block Comparisons .................................................................. 117
A. Initial lisi Block Thickness .......................................................................... 117
B. Initial lisi Block 0.5 mm Firings .................................................................. 118
C. Initial lisi Block 1 mm Firings ..................................................................... 119
5.4.5 Amber Mill Comparisons ......................................................................... 121
A. Amber Mill Thickness ................................................................................. 121
B. Amber Mill 0.5 mm Firings ......................................................................... 122
C. Amber Mill 1 mm Firings ............................................................................ 123
5.5 TRANSLUCENCY PARAMETER ANALYSIS ............................................................. 125
5.5.1 Overall Comparisons ................................................................................ 125
A. Overall comparison between different materials ......................................... 128
B. Overall comparison between different thicknesses ...................................... 130
C. Overall comparison between different firings ............................................. 131
5.1.2 IPS e.max CAD Comparisons .................................................................. 133
A. IPS e.max CAD Thickness .......................................................................... 133
B. IPS e.max CAD 0.5 mm Firings .................................................................. 134
C. IPS e.max CAD 1 mm Firings ..................................................................... 135
5.5.3 n!Ce Comparisons ....................................................................................... 137
A. N!Ce Thickness ........................................................................................... 137
B. N!Ce 0.5 mm Firings ................................................................................... 138
C. N!Ce 1 mm Firings ...................................................................................... 140
5.5.4 Initial lisi Block Comparisons .................................................................. 142
viii
A. Initial lisi Block Thickness .......................................................................... 142
B. Initial lisi Block 0.5 mm Firings .................................................................. 143
C. Initial lisi Block 1 mm Firings ..................................................................... 144
5.5.5 Amber Mill Comparisons ......................................................................... 146
A. Amber Mill Thickness ................................................................................. 146
B. Amber Mill 0.5 mm Firings ......................................................................... 147
C. Amber Mill 1 mm Firings ............................................................................ 149
5.6 PRE-CRYSTALLIZED AND CRYSTALLIZED SPECIMENS ................................... 150
6. DISCUSSION: ...................................................................................................... 154
6.1 COLOR CHANGE ............................................................................................ 154
6.1.1 Devices and Color Systems ...................................................................... 154
6.1.2 Materials and Composition ....................................................................... 155
6.1.3 Firings ....................................................................................................... 158
6.1.4 Thickness of the material .......................................................................... 159
6.1.5 Staining and Glaze .................................................................................... 159
6.2 CIE L*A*B* .................................................................................................. 160
6.2.1 Materials and Composition ....................................................................... 160
6.2.2 Firings .......................................................................................................... 160
6.2.3 Thickness of the material ............................................................................. 161
6.3 TRANSLUCENCY CHANGE .............................................................................. 161
6.3.1 Materials and Composition ....................................................................... 161
6.3.3 Thickness of the material .......................................................................... 163
6.3.4 Staining and Glaze ................................................................................... 163
7. CONCLUSIONS .................................................................................................. 165
8. CLINICAL SIGNIFICANCE ............................................................................... 165
9. DISCLAIMER: ..................................................................................................... 166
10. FUNDING ........................................................................................................ 167
11. REFERENCES: ................................................................................................ 168
ix
List of Tables
TABLE 1. FELDSPHATIC CERAMIC CAD-CAM BLOCKS AVAILABLE IN THE
MARKET ......................................................................................................................... 6
TABLE 2. INDICATIONS AND PROPERTIES OF LITHIUM DISILICATE
MATERIALS (59–65) .................................................................................................... 10
TABLE 3 SHADE DETERMINATION METHODS (105,107–117) ........................... 16
TABLE 4. STUDY GROUPS BASED ON MATERIAL, THICKNESS AND
NUMBER OF FIRINGS. ............................................................................................... 21
TABLE 5. FIRING PARAMETERS (EX: IPS E.MAX CAD, LS: THE INITIAL LISI
BLOCK, NC: N!CE, AM: AMBER MILL .................................................................... 27
TABLE 6. OVERALL MATERIALS MEAN, STANDARD DEVIATION, MINIMUM
AND MAXIMUM VALUES DIVIDED BY THICKNESSES ..................................... 36
TABLE 7. OVERALL MATERIAL MEAN, STANDARD DEVIATION, MINIMUM
AND MAXIMUM VALUES ......................................................................................... 39
TABLE 8. OVERALL PAIRWISE COMPARISON BETWEEN MATERIALS ......... 39
TABLE 9. THICKNESSES MEAN, STANDARD DEVIATION, MINIMUM AND
MAXIMUM VALUES ................................................................................................... 41
TABLE 10. FIRINGS MEAN, STANDARD DEVIATION, MINIMUM AND
MAXIMUM VALUES ................................................................................................... 42
TABLE 11. IPS E.MAX CAD THICKNESSES’ MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ..................................................................... 43
TABLE 12. IPS E.MAX CAD 0.5 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 44
TABLE 13. PAIRWISE COMPARISON BETWEEN FIRINGS OF EX 0.5 MM
SPECIMENS .................................................................................................................. 45
TABLE 14. IPS E.MAX CAD 1 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 46
TABLE 15. PAIRWISE COMPARISON BETWEEN FIRINGS OF EX 1 MM
SPECIMENS .................................................................................................................. 47
TABLE 16. N!CE THICKNESSES’ MEAN, STANDARD DEVIATION, MINIMUM
AND MAXIMUM VALUES ......................................................................................... 48
TABLE 17. N!CE 0.5 MM THICKNESS’S MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ..................................................................... 49
TABLE 18. N!CE 1 MM THICKNESS’S MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ..................................................................... 50
TABLE 19. PAIRWISE COMPARISON BETWEEN FIRINGS OF NC 1 MM
SPECIMENS .................................................................................................................. 51
TABLE 20. INITIAL LISI BLOCK THICKNESSES’ MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 52
x
TABLE 21. INITIAL LISI BLOCK 0.5 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 53
TABLE 22. INITIAL LISI BLOCK 1 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 54
TABLE 23. AMBER MILL THICKNESSES’ MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ..................................................................... 55
TABLE 24. AMBER MILL 0.5 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 56
TABLE 25. PAIRWISE COMPARISON BETWEEN FIRINGS OF AM 0.5 MM
SPECIMENS .................................................................................................................. 57
TABLE 26. AMBER MILL 1 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 58
TABLE 27. PAIRWISE COMPARISON BETWEEN FIRINGS OF AM 1 MM
SPECIMENS .................................................................................................................. 59
TABLE 28. OVERALL MATERIALS MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES OF L* ......................................................... 60
TABLE 29. OVERALL MATERIAL MEAN, STANDARD DEVIATION, MINIMUM
AND MAXIMUM VALUES ......................................................................................... 62
TABLE 30. OVERALL PAIRWISE COMPARISON BETWEEN MATERIALS ....... 62
TABLE 31. THICKNESSES MEAN, STANDARD DEVIATION, MINIMUM AND
MAXIMUM VALUES ................................................................................................... 64
TABLE 32. FIRINGS MEAN, STANDARD DEVIATION, MINIMUM AND
MAXIMUM VALUES ................................................................................................... 65
TABLE 33. OVERALL PAIRWISE COMPARISON BETWEEN FIRINGS .............. 65
TABLE 34. IPS E.MAX CAD THICKNESSES’ MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ..................................................................... 67
TABLE 35. IPS E.MAX CAD 0.5 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 68
TABLE 36. IPS E.MAX CAD 1 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 69
TABLE 37. N!CE THICKNESSES’ MEAN, STANDARD DEVIATION, MINIMUM
AND MAXIMUM VALUES ......................................................................................... 70
TABLE 38. N!CE 0.5 MM THICKNESS’S MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ..................................................................... 71
TABLE 39. PAIRWISE COMPARISON BETWEEN FIRINGS OF NC 0.5 MM
SPECIMENS .................................................................................................................. 71
TABLE 40. N!CE 1 MM THICKNESS’S MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ..................................................................... 72
TABLE 41. PAIRWISE COMPARISON BETWEEN FIRINGS OF NC 1 MM
SPECIMENS .................................................................................................................. 73
xi
TABLE 42. INITIAL LISI BLOCK THICKNESSES’ MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 74
TABLE 43. INITIAL LISI BLOCK 0.5 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 75
TABLE 44. INITIAL LISI BLOCK 1 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 76
TABLE 45. AMBER MILL THICKNESSES’ MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ..................................................................... 77
TABLE 46. AMBER MILL 0.5 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 78
TABLE 47. PAIRWISE COMPARISON BETWEEN FIRINGS OF AM 0.5 MM
SPECIMENS .................................................................................................................. 78
TABLE 48. AMBER MILL 1 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 79
TABLE 49. PAIRWISE COMPARISON BETWEEN FIRINGS OF AM 1 MM
SPECIMENS .................................................................................................................. 80
TABLE 50. OVERALL MATERIALS MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES OF A* ......................................................... 81
TABLE 51. OVERALL MATERIAL MEAN, STANDARD DEVIATION, MINIMUM
AND MAXIMUM VALUES ......................................................................................... 83
TABLE 52. OVERALL PAIRWISE COMPARISON BETWEEN MATERIALS ....... 83
TABLE 53. THICKNESSES MEAN, STANDARD DEVIATION, MINIMUM AND
MAXIMUM VALUES ................................................................................................... 85
TABLE 54. FIRINGS MEAN, STANDARD DEVIATION, MINIMUM AND
MAXIMUM VALUES ................................................................................................... 86
TABLE 55. IPS E.MAX CAD THICKNESSES’ MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ..................................................................... 87
TABLE 56. IPS E.MAX CAD 0.5 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 88
TABLE 57. PAIRWISE COMPARISON BETWEEN FIRINGS OF EX 0.5 MM
SPECIMENS .................................................................................................................. 88
TABLE 58. IPS E.MAX CAD 1 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 89
TABLE 59. PAIRWISE COMPARISON BETWEEN FIRINGS OF EX 1 MM
SPECIMENS .................................................................................................................. 90
TABLE 60. N!CE THICKNESSES’ MEAN, STANDARD DEVIATION, MINIMUM
AND MAXIMUM VALUES ......................................................................................... 91
TABLE 61. N!CE 0.5 MM THICKNESS’S MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ..................................................................... 92
TABLE 62. PAIRWISE COMPARISON BETWEEN FIRINGS OF NC 0.5 MM
SPECIMENS .................................................................................................................. 92
xii
TABLE 63. N!CE 1 MM THICKNESS’S MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ..................................................................... 93
TABLE 64. PAIRWISE COMPARISON BETWEEN FIRINGS OF NC 1 MM
SPECIMENS .................................................................................................................. 94
TABLE 65. INITIAL LISI BLOCK THICKNESSES’ MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 95
TABLE 66. INITIAL LISI BLOCK 0.5 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 96
TABLE 67. PAIRWISE COMPARISON BETWEEN FIRINGS OF LS 0.5 MM
SPECIMENS .................................................................................................................. 96
TABLE 68. INITIAL LISI BLOCK 1 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ............................................. 97
TABLE 69. PAIRWISE COMPARISON BETWEEN FIRINGS OF LS 1 MM
SPECIMENS .................................................................................................................. 98
TABLE 70. AMBER MILL THICKNESSES’ MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ..................................................................... 99
TABLE 71. AMBER MILL 0.5 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 100
TABLE 72. PAIRWISE COMPARISON BETWEEN FIRINGS OF AM 0.5 MM
SPECIMENS ................................................................................................................ 100
TABLE 73. AMBER MILL 1 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 101
TABLE 74. PAIRWISE COMPARISON BETWEEN FIRINGS OF AM 1 MM
SPECIMENS ................................................................................................................ 102
TABLE 75. OVERALL MATERIALS MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES OF B* ....................................................... 103
TABLE 76. OVERALL MATERIAL MEAN, STANDARD DEVIATION, MINIMUM
AND MAXIMUM VALUES ....................................................................................... 105
TABLE 77. OVERALL PAIRWISE COMPARISON BETWEEN MATERIALS ..... 105
TABLE 78. THICKNESSES MEAN, STANDARD DEVIATION, MINIMUM AND
MAXIMUM VALUES ................................................................................................. 107
TABLE 79. FIRINGS MEAN, STANDARD DEVIATION, MINIMUM AND
MAXIMUM VALUES ................................................................................................. 108
TABLE 80. IPS E.MAX CAD THICKNESSES’ MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ................................................................... 109
TABLE 81. IPS E.MAX CAD 0.5 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 110
TABLE 82. PAIRWISE COMPARISON BETWEEN FIRINGS OF EX 0.5 MM
SPECIMENS ................................................................................................................ 110
TABLE 83. IPS E.MAX CAD 1 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 111
xiii
TABLE 84. PAIRWISE COMPARISON BETWEEN FIRINGS OF EX 1 MM
SPECIMENS ................................................................................................................ 112
TABLE 85. N!CE THICKNESSES’ MEAN, STANDARD DEVIATION, MINIMUM
AND MAXIMUM VALUES ....................................................................................... 113
TABLE 86. N!CE 0.5 MM THICKNESS’S MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ................................................................... 114
TABLE 87. PAIRWISE COMPARISON BETWEEN FIRINGS OF NC 0.5 MM
SPECIMENS ................................................................................................................ 114
TABLE 88. N!CE 1 MM THICKNESS’S MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ................................................................... 115
TABLE 89. PAIRWISE COMPARISON BETWEEN FIRINGS OF NC 1 MM
SPECIMENS ................................................................................................................ 116
TABLE 90. INITIAL LISI BLOCK THICKNESSES’ MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 117
TABLE 91. INITIAL LISI BLOCK 0.5 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 118
TABLE 92. PAIRWISE COMPARISON BETWEEN FIRINGS OF LS 0.5 MM
SPECIMENS ................................................................................................................ 118
TABLE 93. INITIAL LISI BLOCK 1 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 119
TABLE 94. PAIRWISE COMPARISON BETWEEN FIRINGS OF LS 1 MM
SPECIMENS ................................................................................................................ 120
TABLE 95. AMBER MILL THICKNESSES’ MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ................................................................... 121
TABLE 96. AMBER MILL 0.5 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 122
TABLE 97. AMBER MILL 1 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 123
TABLE 98. PAIRWISE COMPARISON BETWEEN FIRINGS OF AM 1 MM
SPECIMENS ................................................................................................................ 123
TABLE 99. OVERALL MATERIALS MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES DIVIDED BY THICKNESSES ............... 125
TABLE 100. MATERIAL MEAN, STANDARD DEVIATION, MINIMUM AND
MAXIMUM VALUES ................................................................................................. 128
TABLE 101. PAIRWISE COMPARISON BETWEEN MATERIALS ...................... 128
TABLE 102. THICKNESSES MEAN, STANDARD DEVIATION, MINIMUM AND
MAXIMUM VALUES ................................................................................................. 130
TABLE 103. FIRINGS MEAN, STANDARD DEVIATION, MINIMUM AND
MAXIMUM VALUES ................................................................................................. 131
TABLE 104. PAIRWISE COMPARISON BETWEEN FIRINGS .............................. 131
xiv
TABLE 105. IPS E.MAX CAD THICKNESSES’ MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ................................................................... 133
TABLE 106. IPS E.MAX CAD 0.5 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 134
TABLE 107. IPS E.MAX CAD 1 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 135
TABLE 108. N!CE THICKNESSES’ MEAN, STANDARD DEVIATION, MINIMUM
AND MAXIMUM VALUES ....................................................................................... 137
TABLE 109. N!CE 0.5 MM THICKNESS’S MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ................................................................... 138
TABLE 110. PAIRWISE COMPARISON BETWEEN FIRINGS *SIGNIFICANCE
VALUES HAVE BEEN ADJUSTED BY THE BONFERRONI CORRECTION FOR
MULTIPLE TESTS. ..................................................................................................... 139
TABLE 111. N!CE 1 MM THICKNESS’S MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ................................................................... 140
TABLE 112. PAIRWISE COMPARISON BETWEEN FIRINGS .............................. 140
TABLE 113. INITIAL LISI BLOCK THICKNESSES’ MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 142
TABLE 114. INITIAL LISI BLOCK 0.5 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 143
TABLE 115. INITIAL LISI BLOCK 1 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 144
TABLE 116. AMBER MILL THICKNESSES’ MEAN, STANDARD DEVIATION,
MINIMUM AND MAXIMUM VALUES ................................................................... 146
TABLE 117. AMBER MILL 0.5 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 147
TABLE 118. PAIRWISE COMPARISON BETWEEN FIRINGS .............................. 148
TABLE 119. AMBER MILL 1 MM THICKNESS’S MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 149
TABLE 120. PAIRWISE COMPARISON BETWEEN FIRINGS .............................. 149
TABLE 121. EX PRE-CRYSTALLIZED TO CRYSTALLIZED SPECIMENS ΔE00
MEAN, STANDARD DEVIATION, MINIMUM AND MAXIMUM VALUES ...... 151
TABLE 122. EX PRE-CRYSTALLIZED SPECIMENS TP MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 151
TABLE 123. AM PRE-CRYSTALLIZED TO CRYSTALLIZED SPECIMENS ΔE00
MEAN, STANDARD DEVIATION, MINIMUM AND MAXIMUM VALUES ...... 152
TABLE 124. AM PRE-CRYSTALLIZED SPECIMENS TP MEAN, STANDARD
DEVIATION, MINIMUM AND MAXIMUM VALUES ........................................... 152
xv
List of Figures
FIGURE 1. CLASSIFICATION OF CAD-CAM MATERIALS (22–24) ....................... 3
FIGURE 2. CERAMICS CLASSIFICATION (23,33) .................................................... 5
FIGURE 3. STUDIED MATERIALS ............................................................................ 20
FIGURE 4. PRECISION SAW ...................................................................................... 22
FIGURE 5. DIAMOND BLADE ................................................................................... 23
FIGURE 6. SLICED SPECIMENS ................................................................................ 23
FIGURE 7. POLISHING MACHINE ............................................................................ 24
FIGURE 8. DIGITAL CALIPER ................................................................................... 24
FIGURE 9. IPS E-MAX SPECIMENS BEFORE AND AFTER CRYSTALLIZATION
FIRING BY END USER ................................................................................................ 26
FIGURE 10. AMBER MILL SPECIMEN BEFORE AND AFTER
CRYSTALLIZATION FIRING BY END USER .......................................................... 26
FIGURE 11. PREDETERMINED MEASURING POINTS .......................................... 28
FIGURE 12. COLOR MEASUREMENT ON WHITE AND BLACK BACKGROUND
........................................................................................................................................ 29
FIGURE 13. OUTLINE DEFINITION .......................................................................... 29
FIGURE 14. COLOR ANALYSIS ................................................................................ 30
FIGURE 15. COLOR DIFFERENCE CALCULATION ............................................... 33
FIGURE 16. TRANSLUCENCY CALCULATION ..................................................... 34
FIGURE 17. LITHIUM DISILICATE MATERIALS AFTER MULTIPLE FIRINGS
(B: BASELINE; 1F: FIRST FIRING; 2F: SECOND FIRING; 3F: THIRD FIRING; 4F:
FORTH FIRING; 5F: FIFTH FIRING) .......................................................................... 36
FIGURE 18. OVERALL MEAN ΔE VALUES OF EACH MATERIAL AND
THICKNESS .................................................................................................................. 37
FIGURE 19. OVERALL CHANGES IN ΔE BETWEEN FIRINGS OF 0.5 MM
SPECIMENS .................................................................................................................. 37
FIGURE 20. OVERALL CHANGES IN ΔE BETWEEN FIRINGS OF 1 MM
SPECIMENS .................................................................................................................. 38
FIGURE 21. BOXPLOT OF ΔE FOR EACH MATERIAL. *** (SIGNIFICANT
DIFFERENCE) ............................................................................................................... 40
FIGURE 22. BOXPLOT OF ΔE FOR EACH THICKNESS. ....................................... 41
FIGURE 23. BOXPLOT OF ΔE FOR EACH FIRING. ................................................ 42
FIGURE 24. BOXPLOT OF ΔE FOR EACH IPS E.MAX CAD THICKNESS. ......... 43
FIGURE 25. IPS E.MAX CAD SPECIMENS AFTER MULTIPLE FIRINGS ............ 44
FIGURE 26. CHANGES IN ΔE BETWEEN FIRINGS OF 0.5 MM IPS E.MAX CAD
SPECIMENS .................................................................................................................. 45
xvi
FIGURE 27. IPS E.MAX CAD 0.5 MM SPECIMENS AFTER MULTIPLE FIRINGS
........................................................................................................................................ 46
FIGURE 28. CHANGES IN ΔE BETWEEN FIRINGS OF 1 MM IPS E.MAX CAD
SPECIMENS .................................................................................................................. 47
FIGURE 29. IPS E.MAX CAD 1 MM SPECIMENS AFTER MULTIPLE FIRINGS 47
FIGURE 30. BOXPLOT OF ΔE FOR N!CE THICKNESSES. *** (SIGNIFICANT
DIFFERENCE) ............................................................................................................... 48
FIGURE 31. N!CE SPECIMENS AFTER MULTIPLE FIRINGS ............................... 49
FIGURE 32. CHANGES IN ΔE BETWEEN FIRINGS OF 0.5 MM N!CE
SPECIMENS .................................................................................................................. 49
FIGURE 33. N!CE 0.5 MM SPECIMENS AFTER MULTIPLE FIRINGS ................. 50
FIGURE 34. CHANGES IN ΔE BETWEEN FIRINGS OF 1 MM N!CE SPECIMENS
........................................................................................................................................ 51
FIGURE 35. N!CE 1 MM SPECIMENS AFTER MULTIPLE FIRINGS .................... 51
FIGURE 36. BOXPLOT OF ΔE FOR INITIAL LISI BLOCK THICKNESSES. ***
(SIGNIFICANT DIFFERENCE) ................................................................................... 52
FIGURE 37. INITIAL LISI BLOCK SPECIMENS AFTER MULTIPLE FIRINGS ... 52
FIGURE 38. CHANGES IN ΔE BETWEEN FIRINGS OF 0.5 MM INITIAL LISI
BLOCK SPECIMENS .................................................................................................... 53
FIGURE 39. INITIAL LISI BLOCK 0.5 MM SPECIMENS AFTER MULTIPLE
FIRINGS ......................................................................................................................... 53
FIGURE 40. CHANGES IN ΔE BETWEEN FIRINGS OF 1 MM INITIAL LISI
BLOCK SPECIMENS .................................................................................................... 54
FIGURE 41. INITIAL LISI BLOCK 1 MM SPECIMENS AFTER MULTIPLE
FIRINGS ......................................................................................................................... 54
FIGURE 42. BOXPLOT OF ΔE FOR AMBER MILL THICKNESSES ***
(SIGNIFICANT DIFFERENCE) ................................................................................... 55
FIGURE 43. AMBER MILL SPECIMENS AFTER MULTIPLE FIRINGS ................ 56
FIGURE 44. CHANGES IN ΔE BETWEEN FIRINGS OF 0.5 MM AMBER MILL
SPECIMENS .................................................................................................................. 57
FIGURE 45. AMBER MILL 0.5 MM SPECIMENS AFTER MULTIPLE FIRINGS .. 58
FIGURE 46. CHANGES IN ΔE BETWEEN FIRINGS OF 1 MM AMBER MILL
SPECIMENS .................................................................................................................. 59
FIGURE 47. AMBER MILL 1 MM SPECIMENS AFTER MULTIPLE FIRING ...... 59
FIGURE 48. OVERALL MEAN L* VALUES OF EACH MATERIAL AND
THICKNESS .................................................................................................................. 60
FIGURE 49. OVERALL CHANGES IN L* BETWEEN FIRINGS OF 0.5 MM
SPECIMENS .................................................................................................................. 61
FIGURE 50. OVERALL CHANGES IN L* BETWEEN FIRINGS OF 1 MM
SPECIMENS .................................................................................................................. 61
xvii
FIGURE 51. BOXPLOT OF L* FOR EACH MATERIAL. *** (SIGNIFICANT
DIFFERENCE) ............................................................................................................... 63
FIGURE 52. BOXPLOT OF L* FOR EACH THICKNESS. ........................................ 64
FIGURE 53. BOXPLOT OF L* FOR EACH FIRING. ................................................. 66
FIGURE 54. BOXPLOT OF L* FOR EACH IPS E.MAX CAD THICKNESS. .......... 67
FIGURE 55. CHANGES IN L* BETWEEN FIRINGS OF 0.5 MM IPS E.MAX CAD
SPECIMENS .................................................................................................................. 68
FIGURE 56. CHANGES IN L* BETWEEN FIRINGS OF 1 MM IPS E.MAX CAD
SPECIMENS .................................................................................................................. 69
FIGURE 57 .BOXPLOT OF L* FOR N!CE THICKNESSES. *** (SIGNIFICANT
DIFFERENCE) ............................................................................................................... 70
FIGURE 58. CHANGES IN L* BETWEEN FIRINGS OF 0.5 MM N!CE SPECIMENS
........................................................................................................................................ 72
FIGURE 59. CHANGES IN L* BETWEEN FIRINGS OF 1 MM N!CE SPECIMENS
........................................................................................................................................ 73
FIGURE 60. BOXPLOT OF L* FOR INITIAL LISI BLOCK THICKNESSES. ***
(SIGNIFICANT DIFFERENCE) ................................................................................... 74
FIGURE 61. CHANGES IN L* BETWEEN FIRINGS OF 0.5 MM INITIAL LISI
BLOCK SPECIMENS .................................................................................................... 75
FIGURE 63. CHANGES IN L* BETWEEN FIRINGS OF 1 MM INITIAL LISI
BLOCK SPECIMENS .................................................................................................... 76
FIGURE 65. BOXPLOT OF L* FOR AMBER MILL THICKNESSES ***
(SIGNIFICANT DIFFERENCE) ................................................................................... 77
FIGURE 66. CHANGES IN L* BETWEEN FIRINGS OF 0.5 MM AMBER MILL
SPECIMENS .................................................................................................................. 79
FIGURE 67. CHANGES IN L* BETWEEN FIRINGS OF 1 MM AMBER MILL
SPECIMENS .................................................................................................................. 80
FIGURE 68. OVERALL MEAN A* VALUES OF EACH MATERIAL AND
THICKNESS .................................................................................................................. 81
FIGURE 69. OVERALL CHANGES IN A* BETWEEN FIRINGS OF 0.5 MM
SPECIMENS .................................................................................................................. 82
FIGURE 70. OVERALL CHANGES IN A* BETWEEN FIRINGS OF 1 MM
SPECIMENS .................................................................................................................. 82
FIGURE 71. BOXPLOT OF A* FOR EACH MATERIAL. *** (SIGNIFICANT
DIFFERENCE) ............................................................................................................... 84
FIGURE 72. BOXPLOT OF A* FOR EACH THICKNESS. ........................................ 85
FIGURE 73. BOXPLOT OF A* FOR EACH FIRING. ................................................ 86
FIGURE 74. BOXPLOT OF A* FOR EACH IPS E.MAX CAD THICKNESS. .......... 87
FIGURE 75. CHANGES IN A* BETWEEN FIRINGS OF 0.5 MM IPS E.MAX CAD
SPECIMENS .................................................................................................................. 89
xviii
FIGURE 76. CHANGES IN A* BETWEEN FIRINGS OF 1 MM IPS E.MAX CAD
SPECIMENS .................................................................................................................. 90
FIGURE 77. BOXPLOT OF A* FOR N!CE THICKNESSES. *** (SIGNIFICANT
DIFFERENCE) ............................................................................................................... 91
FIGURE 78. CHANGES IN A* BETWEEN FIRINGS OF 0.5 MM N!CE
SPECIMENS .................................................................................................................. 93
FIGURE 79. CHANGES IN A* BETWEEN FIRINGS OF 1 MM N!CE SPECIMENS
........................................................................................................................................ 94
FIGURE 80. BOXPLOT OF A* FOR INITIAL LISI BLOCK THICKNESSES. ***
(SIGNIFICANT DIFFERENCE) ................................................................................... 95
FIGURE 81. CHANGES IN A* BETWEEN FIRINGS OF 0.5 MM INITIAL LISI
BLOCK SPECIMENS .................................................................................................... 97
FIGURE 82. CHANGES IN A* BETWEEN FIRINGS OF 1 MM INITIAL LISI
BLOCK SPECIMENS .................................................................................................... 98
FIGURE 83. BOXPLOT OF A* FOR AMBER MILL THICKNESSES ***
(SIGNIFICANT DIFFERENCE) ................................................................................... 99
FIGURE 84. CHANGES IN A* BETWEEN FIRINGS OF 0.5 MM AMBER MILL
SPECIMENS ................................................................................................................ 101
FIGURE 85. CHANGES IN A* BETWEEN FIRINGS OF 1 MM AMBER MILL
SPECIMENS ................................................................................................................ 102
FIGURE 86. OVERALL MEAN B* VALUES OF EACH MATERIAL AND
THICKNESS ................................................................................................................ 103
FIGURE 87. OVERALL CHANGES IN B* BETWEEN FIRINGS OF 0.5 MM
SPECIMENS ................................................................................................................ 104
FIGURE 88. OVERALL CHANGES IN B* BETWEEN FIRINGS OF 1 MM
SPECIMENS ................................................................................................................ 104
FIGURE 89. BOXPLOT OF B* FOR EACH MATERIAL. *** (SIGNIFICANT
DIFFERENCE) ............................................................................................................. 106
FIGURE 90. BOXPLOT OF B* FOR EACH THICKNESS. ...................................... 107
FIGURE 91. BOXPLOT OF B* FOR EACH FIRING. ............................................... 108
FIGURE 92. BOXPLOT OF B* FOR EACH IPS E.MAX CAD THICKNESS. ........ 109
FIGURE 93. CHANGES IN B* BETWEEN FIRINGS OF 0.5 MM IPS E.MAX CAD
SPECIMENS ................................................................................................................ 111
FIGURE 94. CHANGES IN B* BETWEEN FIRINGS OF 1 MM IPS E.MAX CAD
SPECIMENS ................................................................................................................ 112
FIGURE 95. BOXPLOT OF B* FOR N!CE THICKNESSES. *** (SIGNIFICANT
DIFFERENCE) ............................................................................................................. 113
FIGURE 96. CHANGES IN B* BETWEEN FIRINGS OF 0.5 MM N!CE SPECIMENS
...................................................................................................................................... 115
FIGURE 97. CHANGES IN B* BETWEEN FIRINGS OF 1 MM N!CE SPECIMENS
...................................................................................................................................... 116
xix
FIGURE 98. BOXPLOT OF B* FOR INITIAL LISI BLOCK THICKNESSES. ***
(SIGNIFICANT DIFFERENCE) ................................................................................. 117
FIGURE 99. CHANGES IN B* BETWEEN FIRINGS OF 0.5 MM INITIAL LISI
BLOCK SPECIMENS .................................................................................................. 119
FIGURE 100. CHANGES IN B* BETWEEN FIRINGS OF 1 MM INITIAL LISI
BLOCK SPECIMENS .................................................................................................. 120
FIGURE 101. BOXPLOT OF B* FOR AMBER MILL THICKNESSES ***
(SIGNIFICANT DIFFERENCE) ................................................................................. 121
FIGURE 102. CHANGES IN B* BETWEEN FIRINGS OF 0.5 MM AMBER MILL
SPECIMENS ................................................................................................................ 122
FIGURE 103. CHANGES IN B* BETWEEN FIRINGS OF 1 MM AMBER MILL
SPECIMENS ................................................................................................................ 124
FIGURE 104. OVERALL MEAN TP OF EACH MATERIAL AND THICKNESS . 125
FIGURE 105. LITHIUM DISILICATE MATERIALS' TRANSLUCENCY AFTER
MULTIPLE FIRINGS .................................................................................................. 126
FIGURE 106. OVERALL CHANGES IN TP BETWEEN FIRINGS OF 0.5 MM
SPECIMENS ................................................................................................................ 126
FIGURE 107. OVERALL CHANGES IN TP BETWEEN FIRINGS OF 1 MM
SPECIMENS ................................................................................................................ 127
FIGURE 108. BOXPLOT OF TP FOR EACH MATERIAL. *** (SIGNIFICANT
DIFFERENCE) ............................................................................................................. 129
FIGURE 109. BOXPLOT OF TP FOR EACH THICKNESS. *** (SIGNIFICANT
DIFFERENCE) ............................................................................................................. 130
FIGURE 110. BOXPLOT OF TP FOR EACH FIRING. *** (SIGNIFICANT
DIFFERENCE) ............................................................................................................. 132
FIGURE 111. BOXPLOT OF TP FOR EACH IPS E.MAX CAD THICKNESS. ***
(SIGNIFICANT DIFFERENCE) ................................................................................. 133
FIGURE 112. IPS E.MAX CAD SPECIMENS’ TRANSLUCENCY AFTER
MULTIPLE FIRINGS .................................................................................................. 134
FIGURE 113. CHANGES IN TP BETWEEN FIRINGS OF 0.5 MM IPS E.MAX CAD
SPECIMENS ................................................................................................................ 135
FIGURE 114. IPS E.MAX CAD 0.5 MM SPECIMENS’ TRANSLUCENCY AFTER
MULTIPLE FIRINGS .................................................................................................. 135
FIGURE 115. CHANGES IN TP BETWEEN FIRINGS OF 1 MM IPS E.MAX CAD
SPECIMENS ................................................................................................................ 136
FIGURE 116. IPS E.MAX CAD 1 MM SPECIMENS’ TRANSLUCENCY AFTER
MULTIPLE FIRING .................................................................................................... 136
FIGURE 117. BOXPLOT OF TP FOR EACH N!CE THICKNESS. ***
(SIGNIFICANT DIFFERENCE) ................................................................................. 137
FIGURE 118. N!CE SPECIMENS’ TRANSLUCENCY AFTER MULTIPLE FIRINGS
...................................................................................................................................... 138
xx
FIGURE 119. CHANGES IN TP BETWEEN FIRINGS OF 0.5 MM N!CE
SPECIMENS ................................................................................................................ 139
FIGURE 120. N!CE 0.5 MM SPECIMENS’ TRANSLUCENCY AFTER MULTIPLE
FIRINGS ....................................................................................................................... 139
FIGURE 121. CHANGES IN TP BETWEEN FIRINGS OF 1 MM N!CE SPECIMENS
...................................................................................................................................... 141
FIGURE 122. N!CE 1 MM SPECIMENS’ TRANSLUCENCY AFTER MULTIPLE
FIRINGS ....................................................................................................................... 141
FIGURE 123. BOXPLOT OF TP FOR EACH INITIAL LISI BLOCK THICKNESS.
*** (SIGNIFICANT DIFFERENCE) .......................................................................... 142
FIGURE 124. INITIAL LISI BLOCK SPECIMENS’ TRANSLUCENCY AFTER
MULTIPLE FIRINGS .................................................................................................. 143
FIGURE 125. CHANGES IN TP BETWEEN FIRINGS OF 0.5 MM INITIAL LISI
BLOCK SPECIMENS .................................................................................................. 143
FIGURE 126. INITIAL LISI BLOCK 0.5 MM SPECIMENS’ TRANSLUCENCY
AFTER MULTIPLE FIRINGS .................................................................................... 144
FIGURE 127. CHANGES IN TP BETWEEN FIRINGS OF 1 MM INITIAL LISI
BLOCK SPECIMENS .................................................................................................. 145
FIGURE 128. INITIAL LISI BLOCK 1 MM SPECIMENS’ TRANSLUCENCY
AFTER MULTIPLE FIRINGS .................................................................................... 145
FIGURE 129. BOXPLOT OF TP FOR EACH AMBER MILL THICKNESS. ***
(SIGNIFICANT DIFFERENCE) ................................................................................. 146
FIGURE 130. AMBER MILL SPECIMENS’ TRANSLUCENCY AFTER MULTIPLE
FIRINGS ....................................................................................................................... 147
FIGURE 131. CHANGES IN TP BETWEEN FIRINGS OF 0.5 MM AMBER MILL
SPECIMENS ................................................................................................................ 148
FIGURE 132. AMBER MILL 0.5 MM SPECIMENS’ TRANSLUCENCY AFTER
MULTIPLE FIRINGS .................................................................................................. 148
FIGURE 133. CHANGES IN TP BETWEEN FIRINGS OF 1 MM AMBER MILL
SPECIMENS ................................................................................................................ 150
FIGURE 134. AMBER MILL 1 MM SPECIMENS’ TRANSLUCENCY AFTER
MULTIPLE FIRINGS .................................................................................................. 150
FIGURE 135. PRE-CRYSTALLIZED AND CRYSTALLIZED EX SPECIMENS ... 151
FIGURE 136. PRE-CRYSTALLIZED AND CRYSTALLIZED AM SPECIMENS.
BLACK BACKGROUND SHOWS A CLEARER DIFFERENCE IN
TRANSLUCENCY ...................................................................................................... 153
FIGURE 137. SPOTTED PATTERN EXHIBITED BY AM SPECIMENS AFTER
MULTIPLE FIRINGS. BLACK ARROW: OPAQUE AREAS; WHITE ARROW:
TRANSLUCENT AREAS ........................................................................................... 157
FIGURE 138. (A) LISI INITIAL BLOCK SPECIMEN WITH CRACK
DEVELOPMENT. (B) FRACTURED LISI INITIAL BLOCK SPECIMEN ............. 164
xxi
Abbreviations
EX: IPS e.max CAD
NC: n!ce
LS: Initial LiSi Block
AM: Amber Mill
ISO: International Organization for Standardization
TP: Translucency Parameter
ΔE00: Color change
xxii
Abstract
Tittle: Effect of Repeated Firing on the Color and Translucency of Different CAD/CAM
Lithium Disilicate Reinforced Glass Ceramic Materials.
Aim: Assess the effect of multiple firings on the color and translucency of different
lithium disilicate reinforced glass ceramic CAD-CAM materials with thicknesses of 0.5
mm and 1 mm.
Materials and Methods: A total of 160 specimens (length 14.00 mm x width 12.00 mm
x with thicknesses of 0.5 mm and 1.0 mm) of 4 different A1, HT lithium-disilicate
reinforced glass ceramic blocks, IPS e.max CAD (EX; IPS e.max CAD, Ivoclar Vivadent,
Schaan, Liechtenstein), n!ce (NC; Straumann, Freiburg, Germany), Initial LiSi Block
(LS; GC, Tokyo, Japan), and Amber Mill (AM; HASSBIO, Kangreung, Korea) were
subjected to a crystallization firing following the manufacturer’s recommendation and
then all specimens were fired five times according to their individual straining and glazing
parameters. The color and translucency of each specimen was measured in white and
black backgrounds after each firing. The color change (ΔE00), and the translucency
parameter (TP) were calculated. Data was statistically analyzed by applying non-
parametric tests with ⍺=0.05.
Results: For ΔE00, overall comparisons showed significant differences between
materials, except for NC and LS, which were not different from each other (p>0.05). EX
(p=0.013) and NC (p<0.001) 1 mm specimens increased significantly after the fifth firing.
AM 0.5 mm specimens increased significantly (p=0.001) after the third firing and AM 1
mm specimens increased significantly (p=0.000) after the second firing.
For TP, overall comparisons showed significant differences between materials (p<0.001).
TP in 0.5 mm specimens was higher than in 1 mm specimens (p<0.001). For NC, TP
decreased after the fourth (p=0.008) and fifth (p=0.033) firing in 0.5 mm specimens, and
after the fourth (p=0.004) and fifth (p=0.000) firing for 1 mm specimens. For AM, 0.5
mm thickness, TP increased after the second firing (p=0.019) but decreased in 1 mm
specimens after the fourth (p=0.001) and fifth (p=0.000) firing.
Conclusions: Multiple firings influence the color and translucency of different lithium
disilicate reinforced glass ceramic CAD/CAM materials, however, the changes might
affect the materials differently. Most of the thicker specimens experienced more
pronounced color changes (ΔE00); translucency decreases with increasing thickness of
the material. Within the CAD/CAM block, color and translucency are non-homogeneous.
xxiii
Clinical Significance: Differences in color and translucency of different lithium
disilicate reinforced glass ceramic CAD/CAM materials as well as the thickness of the
restoration must be considered when subjecting them to multiple firings. To achieve
restorations with excellent esthetics (ΔE00<2 and no change in TP), a maximum number
of firings is recommended: EX four firings, NC three firings, LS five firings, and AM one
firing. However, uneven distribution of color and translucency within each individual
block might make a predictable esthetic outcome even more challenging.
Keywords: Color, Translucency, Lithium Disilicate, Repeated firings.
1. Introduction
1.1 Digital Dentistry
Digital Dentistry was first introduced in the 1970’s with the CAD/CAM (Computer
aided design/Computer aided manufacture) technology by Duret and Preston (1). Later in
1984 the CEREC system was developed by Moermann (2,3). Over the years new devices
have been introduced into the dental world. Nowadays, the application of digital dentistry
into dental practices is a reality (4), which has had a great impact in the way dentistry is
practiced, and especially in the way that restorative dentistry is practiced. Every
CAD/CAM system is formed by 3 elements, the first one is the data acquisition, where a
device (scanner) is used to convert the information that we acquire (teeth) into a digital
file that can later be processed by a computer. The second element is the data processing,
which is a software, that will allow us to process the information acquired by the scanner
and design an object (restoration). The third and last element is the manufacturing, this
last component will allow us to fabricate the designed object (5,6).
Based on where the components of the CAD-CAM systems are located, the
production can be classified in 3 types: chairside, laboratory and centralized. In CAD-
CAM chairside system, all components are located in the dental office. In the laboratory
production, impressions are sent to the laboratory, where a master cast is fabricated,
scanned and the restoration is fabricated. Finally, in the centralized system the dentist
sends the scanned files to a milling centre, where the restorations are fabricated (5).
The substitution of the alginate or PVS impression by intraoral scanners has represented
a huge change in how dentistry is practiced. Different types of technology are used to
obtain a digital impression of the teeth and oral tissues (7). The development of intraoral
scanners started with the CEREC system in the 1980’s as mentioned above. Later in 2006
Cadent developed iTero, an intraoral scanner that by 2008 was able to scan a full arch. In
2012, 3M introduced its own scanner, True Definition, and since then many other
manufacturers have introduced their own scanners and their own software’s for various
applications (8).
2
Research has shown that digital impression show acceptable results, having less
discrepancies than conventional impressions, providing advantages like better patient
acceptance, and a decrease chair time (9,10). Scanners project a light that will be recorded
by videos or images, that are then stitched together by a software. With that information
the software will create a digital model that will be later used to fabricate the restoration
(11,12).
CAM technology can be subtractive or additive. Subtractive manufacturing
consists of using a block of a certain material and cutting away all the pieces that are not
needed (13). The primarily digital method for manufacturing ceramic restorations
nowadays is subtractive manufacturing (14), the most common subtractive technology
used, is computer numerically controlled machining which consist of different types of
machines, for example milling machines, that cut a material until the intended shape is
achieved. This type of manufacturing is very fast compared to conventional methods, but
its downside is the fact that there is a high amount of material waste (6).
On the other hand, additive manufacturing consists of using 3D data to create an
object layer by layer by attaching materials together (6). Three-dimensional printing is
the most used method of additive manufacturing in dentistry (14). The dental materials
available nowadays for this type of manufacturing are polymers, polyesters, metals
(titanium and cobalt alloys) and even some ceramics (alumina and zirconia) (15). The
advantages of additive manufacturing are that it allows the fabrication of personalized
objects, and objects with complex shapes, different materials can be used for the same
object, it is less sensitive to human error, it is fast, and it generates less material waste
and requires less energy (less environmental impact) (16). Still, this technology remains
under constant development and requires some improvements in the quality of the
surface, on the mechanical properties and on the dimensional stability of the printed
objects (15).
Generally speaking, the advantages of using digital technology in dentistry are that it
creates restorations with a better marginal fit and less flaws or defects that than
conventional methods, it allows the dentist to fabricate its own restoration without the
need of a laboratory and also that patients have reported to prefer digital impressions
instead of conventional ones (9,17–19). On the other side, the restorations fabricated with
this systems can be only single- or short-span restorations (18,19).
3
1.2 CAD-CAM Materials
1.2.1 Classification
Multiple materials are available for digital manufacturing, and to choose the
correct one for a specific situation can be difficult (20). Also new CAD-CAM materials
are being introduced, and before their clinical application it is important to test their
properties (21). The different CAD-CAM materials available are polymer based
materials, resin based composites, wax, metals, and ceramics (18,19,21,22).
A summary of the classification of CAD-CAM material is shown in Figure 1.
Figure 1. Classification of CAD-CAM materials (22–24)
Among the polymer-based materials, CAD-CAM PMMA (polymethyl
methacrylate) is used as a long term fixed partial denture or single crown temporary
material, (25) when compared to conventional PMMA, the CAD-CAM blocks have a
highly cross-linked nature that gives the material more durability and better processing
CAD-CAM
Materials
Polymer-based
materials
PMMA
PEEK
Peekton
Resin Based
Composites
RCB
Wax
Metals
Titanium
Gold
Chrome-cobalt
Ceramics
Resin-matrix
ceramics
Polycrystalline
ceramics
Glass -matrix ceramic
4
than the conventional material (26). Pekkton (thermoplastic polyaryletherketone) and
PEEK (polyether-etherketone) are materials that show less wear than PMMA and
conventional composites, they are also easier to mill than metals. These materials are
usually used for crowns, telescopic copings, three-unit bridges, implant supported
superstructures, and custom implant abutments (27–29).
RCB (resin based composite blocks) differentiate from conventional resin based
composites because they are polymerized designed, and milled extraorally which gives
them better mechanical properties and voids monomer leach and polymerization
shrinkage (30,31).
Wax is most cost and time-effective than a traditional wax-up. Once is milled or
printed it can be used for ceramic pressing or metal-casting (21).
Metals avoid the possibility of miscasting and require less effort than conventional
methods. A softer version of chrome-cobalt has been introduced, which mills like wax,
and later, it is sintered in an argon gas achieving the same strength as regular of chrome-
cobalt. Nowadays metals can also be printed as mentioned above (24).
Ceramics have been used in dentistry for many years. At the beginning they were
used only in the anterior region for esthetic purposes, but over the years, new ceramics
with better mechanical properties have been introduced. In the last couple of years, there
is an increasing amount of patients that expect natural looking outcomes from their
restorative treatments, therefore the use of ceramic restorations has increased (32).
Nowadays ceramics are able to provide both esthetics and strength.
Based on their formulation, ceramics can be classified in 3 group (Figure 2):
• Glass-matrix ceramic
• Polycrystalline ceramics
• Resin-matrix ceramics (also called ceramic-reinforced polymers)
5
Figure 2. Ceramics Classification (23,33)
1.2.2 Glass Ceramics
a. Feldsphatic Ceramics
The first ceramic to be used in dentistry was feldsphatic ceramic which was
initially used to fabricate denture teeth. The natural combination of sodium
aluminosilicates and potassium forms feldspar, which later is combined with kaolin and
quartz forming feldsphatic ceramics (23).
Feldsphatic ceramics have a high proportion of the glassy phase, allowing light
transmission and generating a high translucency restoration (33), making it appropriate
for its use as an esthetic material (23). Still, these characteristics make the material more
brittle (17), with a flexural strength of 60 MPa to 70 MPa (34), making it necessary to
use a metal core underneath it, to achieve a higher strength (PFM-porcelain fused to
metal) (17). Felspathic ceramics are used as veneering materials, or for all ceramic
onlays, inlays, anterior single crowns, and veneers. There are three ways of fabricating a
feldsphatic ceramic restoration: the first one is to mix ceramic powder with a water-based
liquid to create a mass. Layers of this mass will be added, shaping the final restoration.
The second method of fabrication uses the lost wax-technique for casting or pressing, and
Ceramics
Glass-matrix
ceramics
Feldsphatic
ceramics
Synthetic
ceramics
Leucite based
Lithium disilicate
Fluorapatite
Glass infiltrated
ceramics
Alumina
Alumina and
magnesium
Zirconia
Polycrystalline
ceramics
Alumina
Alumina
toughened
zirconia
Resin-matrix
ceramics
Polymer
infiltrated
ceramics (PIC)
Resin
nanoceramics
(RNC)
6
the last one mills the restoration from a prefabricated block (34). Some commercial
feldsphatic ceramic CAD-CAM blocks are listed in Table 1.
Feldsphatic Ceramic CAD-CAM blocks
Commercial Name Manufacturer
Mark II VITA Zahnfabrik (Bad Säckingen, Germany)
Real Life ceramic blocks VITA Zahnfabrik
TriLux Forte VITA Zahnfabrik
CEREC Blocs Dentsply Sirona (York, USA)
CEREC Blocs C/C In/C PC Dentsply Sirona
Table 1. Feldsphatic Ceramic CAD-CAM blocks available in the market
With time, the need of stronger materials, that did not require to have a metal core,
emerged. The problem with PFM restorations is that they often compromised the esthetic
result and raised concerns about metals being present in the mouth (17). Therefore, an
attempt was made to increase the strength of ceramics and eliminate the need of a metal
core by a phenomenon called dispersion strengthening (introducing crystals in the glass
matrix) or by crystallization of the glass (35,36).
Dispersion strengthening was introduced in the 1960’s (37), and it consisted of
introducing aluminum oxide crystals into the feldsphatic glassy matrix (38,39). Even
though the strength of the restorations increased, it was not enough and these restorations
were not indicated for posterior teeth (40). Also their esthetic appearance was
compromised since they presented a opaque appearance (41).
In the process known as crystallization of the glass, the ceramic goes through a heat
treatment that allows the nucleation and growth of the crystals that are present on the
glass (42–44). The crystals that are introduced or nucleated on the glassy matrix will
strengthen the material by stopping the propagation of the cracks that might form (42,45).
The amount of crystals will dictate the strength, opacity and opalescence of the material
(23,46). The size of the crystals will also have an influence in its strength (47). Research
has shown that the elastic modulus and the strength of the ceramic increases when the
crystal size is smaller than 5μm (48,49).
7
b. Lithium Disilicate
b.1. Background
Lithium disilicate is a synthetic glass matrix ceramic material (23) that has become
very popular in modern restorative dentistry because of its ability to combine strength,
good processing and mechanical properties, and esthetics (42). This material has a
mechanical strength of around 400 MPa, a fracture toughness of 3 to 4 MPa m
0.5
, a biaxial
strength of 250–350 MPa, and a three-point bending strength of around 300–400 MPa
(50). Lithium disilicate reinforced glass ceramic material is indicated for single
restorations, inlays, onlays, veneers, crowns, implant abutments and crowns, and bridges
up to the second premolar. Lithium disilicate can be used to restore a full mouth with a
conservative approach since the restorations can be fabricate with a minimum thickness
of 0.5mm (51), and at the same time provide an adequate strength (52).
b.2. Chemical Composition
Lithium disilicate is represented by a simple formula (Li2O–2SiO2), still lithium
disilicate for dental use has other components that are added to achieve its desirable
properties. Usually, these type of glass ceramics are very hard to make because of their
instability, and the difficulty in controlling the crystallization process. Silica, alumina,
phosphorus pentoxide, lithium oxide, and potassium oxide are used to prepare lithium
disilicate (53).
Lithium oxide (Li2O) and silicon dioxide (SiO2) are the basic components for the
crystallization of lithium disilicate, but for the reasons stated above other components like
phosphorus pentoxide are added as nucleating agents. The nucleating agent of choice is
usually P2O5, because besides being a nucleating agent, it has the ability to increase the
strength of the material, which is a characteristic that the rest of nucleating agents do to
have. Barium oxide (BaO) and Caesium oxide (Cs2O) are added to stabilize the glass
phase and at the same time improve the refractive index and the translucency. Alumina
oxide (Al2O3) and boron trioxide (B2O3) in concentrations less than 3% are added to
decrease the chemical solubility. Calcium oxide is commonly added to compensate for
the viscosity increase caused by the alumina oxide (53).
To obtain a low temperature fusion ceramic, alkali oxides like barium oxide (BaO),
calcium oxide (CaO), caesium oxide (Cs2O), potassium oxide (K2O), and sodium oxide
(Na2O) can be used. Europium oxide (Eu2O3), cerium oxide (Ce2O3) and yttrium oxide
(Y2O3), are added for fluorescence and to improve the refractive index.
8
To obtain colored shades, determined oxides like TiO2, CeO2, Fe2O3, V2O5,
MnO2, or NiO2, can be added. Pigments and d-element ions in small amounts are also
used for this purpose (53).
To achieve uniformly distributed crystals niobium and platinum oxide can be
used. To increase the translucency of the glasses, heavy metal oxides (Ba, Ce, Cs, Nb, Sr,
Ta, Y, and/or Eu oxides) can be added in small amounts, these oxides can also function
as coloring agents (53).
Adding oxides can lead to different consequences on the optical, processing
properties and the viscosity of the material , that is why each researcher or manufacturer
should find the combination and balance that better serves the properties of their material
(53).
b.3. Products
There are two types of lithium disilicate reinforced glass ceramics for dental use,
pressable and millable lithium disilicate.
IPS Empress II (pressable), was first introduced in the market in the 1990’s. Later, in
2001 a new generation of this material was launched by Ivoclar Vivadent (IPS e.max
Press). The difference between these materials was that the later had a higher amount of
crystals which at the same time were smaller in size, creating a product with better
mechanical and optical properties. With the introduction of digital dentistry and the need
for a material that meet this criteria, in 2005 Ivoclar Vivadent launched the IPS e.max
CAD (machinable) (42). The difference between press and CAD lithium disilicate is the
proportion of lithium to silicon oxides. A higher proportion of lithium oxide will be used
for the pressable type, since it will increase the castability and fluidity of the glass (53).
When comparing pressed lithium disilicate to milled lithium disilicate restorations, the
literature shows that pressed restorations have a better marginal fit. Still both types of
restorations have an clinically acceptable marginal fit (54). Regarding the fracture
toughness, pressed lithium disilicate showed better results than milled lithium disilicate
(55), and both materials show similar results in terms of flexural strength (56). In
conclusion, both materials show clinically acceptable results, but in some cases milled
lithium disilicate can be chosen over the pressable type because of the convenient
chairside production that allows restorations to be fabricated and delivered in the same
appointment (57).
9
IPS e.max CAD blocks are sold as lithium metasilicate glass ceramic. Depending
on the proportion of lithium to silicon oxides the manufacturer can either fabricate lithium
disilicate or lithium metasilicate. The conversion from lithium metasilicate to a lithium
disilicate glass ceramic involves a very small linear shrinkage of only about 0.2–0.3%.
To form lithium metasilicate, the glass needs to be subjected to a nucleation heat
treatment to form nuclei appropriate for creating lithium metasilicate crystals (500-
600ºC). Once milled, the restoration will be subjected to a second heat treatment at a
higher temperature that will form lithium disilicate crystals. Lithium metasilicate has a
better machinability than lithium disilicate because its crystals have a platelet or lamellar
form. If lithium disilicate is milled directly, it will be hard on the machining tools and the
machined restorations may have poor edge strength (53).
In 2019 the patent of IPS e.max CAD expired (58), allowing other companies to
produce and commercialize their own products. Nowadays there are different types of
lithium disilicate in the market. There are materials that require to be crystallized after
the milling process (labside systems), these materials usually do not come in the final
shade, and that shade is only achieved after the crystallization process (IPS e. max CAD,
Ivoclar Vivadent, Schaan, Liechtenstein; Amber Mill, HASSBIO, Kangneung, Korea).
On the other hand there are materials that are already fully crystalized (chairside systems)
and that do not require any crystallization cycle after milling (n!ce, Straumann, Basel,
Switzerland; Initial LiSi Block, GC, Tokyo, Japan; ; CEREC Tessera, Dentsply Sirona,
York, USA) (59). The indications and properties of these materials are described in Table
2.
10
Indications
Flexural
Strength
Fracture
Toughness
(MPa·m
1/2
)
Young’s
Modulus
Shear
Modulus
IPS e.max
CAD
(Ivoclar
Vivadent,
Schaan,
Liechtenstein)
Crowns (anterior
and posterior),
veneers, onlays,
inlays, FPD’S (3-
unit) anterior
teeth and
premolars,
implant
crowns/abutment
360 ± 60
MPa
2.04 ± 0.10 102.5 GPa 42.2 GPa
n!ce
(Straumann,
Freiburg,
Germany )
Crowns. Veneers,
onlays, inlays,
implant
crowns
350 ± 50
MPa
1.53 ± 0.05 91.7 GPa 38.9 GPa
Initial LiSi
Block (GC )
Crowns (anterior
and posterior),
veneers, onlays,
inlays, implant
crowns
400
MPa
1.50 ± 0.04 95.6 GPa 39.9 GPa
Amber Mill
(HASSBIO,
Kangreung,
Korea)
Crowns (anterior
and posterior),
veneers, onlays,
inlays, FPD’S (3-
unit) anterior
teeth and
premolars
450
MPa
2.1 ± 0.3 98.3 GPa 41.4 GPa
CEREC
Tessera
(Dentsply
Sirona, York,
USA)
Crowns, veneers
onlays, inlays
>700
MPa
1.45 ± 0.10 103.1 GPa 41.94 GPa
Table 2. Indications and properties of Lithium Disilicate Materials (59–65)
11
c. Zirconia Reinforced Lithium Silicate
Zirconia reinforced lithium silicate glass ceramic SiO2-Li2O–Al2O3–K2O–
P2O5–ZrO2 was developed in Germany by the Fraunhofer Institute for Silicate Research
in collaboration with DeguDent GmbH and Vita Zahnfabrik. The product was out in the
market in 2013 (66). The aim of creating this product was to obtain a monolithic esthetic
and reliable material that could stand high mechanical stress for posterior multiple units
FPD’s (67).
In its composition it has 8-12% zirconia content (68,69), and 56-64% crystal phase
content. The crystal phase content is lower compared to regular lithium disilicate material
which has 57-80% (69). The zirconia particles are added as fillers which are supposed to
increase the fracture resistance and interrupt crack growth (70). Studies have shown that
the flexural strength (405-533 MPa), fracture toughness, hardness, and elastic modulus
of zirconia reinforced lithium silicate are higher than conventional lithium disilicate (70–
72). On the other hand, conventional lithium disilicate exhibits less brittleness than the
zirconia reinforced type, which may mean that the conventional type has a better
machinability (70).
Zirconia has a negative effect on the translucency level when added to lithium
silicate, generating a more opaque material. It was shown that a 10 wt% zirconia content
has the highest effect on the translucency. If the zirconia content is higher than 10 wt%
the influence of zirconia in the translucency of the material is reduced (73).
Some of the zirconia reinforced lithium silicate commercial brands available in the market
are VITA Suprinity (VITA Zahnfabrik, Bad Säckingen, Germany), Celtra Duo (Dentsply
Sirona, York, USA), and Suprinity PC (VITA Zahnfabrik, Bad Säckingen, Germany),
(65,68,69).
1.2.3 Crystallization, Staining and Glazing
Crystallization of lithium disilicate is a heterogeneous process. The crystallization
of this type of ceramic can occur through a two-stage (pressed lithium disilicate) or a
three-stage process (milled lithium disilicate), depending on if the lithium disilicate is
designed to be pressed or to be milled. At the beginning of the process (first stage) both
types are manufactured in the same way. A glass melt of quartz, potassium oxide, lithium
oxide, alumina, phosphor oxide, and coloring oxides is pressure-casted into steel molds
to obtain ingots or blocks. Before the glass melts cools down, it is introduced into a
12
furnace (450-550ºC) for five minutes to one hour, to avoid stress build up and relax the
glass, and to form as many nuclei as possible (74).
a. Two-stage Process
After the first stage, mentioned above, the ingots are introduced into a furnace
(750–850°C) for about 2 hours, to obtain lithium disilicate crystals. For the second stage
the lost wax technique is used, where a mold of the restorations is created from a previous
wax-up. The ingots are hot pressed at 920ºC, and the material flows into the mold to form
the restoration. The material is kept at this temperature from 5 to 15 minutes. In this stage,
the lithium disilicate crystals reach a length of 3 to 6 μm and achieve the long needle-like
shape. The volume fraction of the crystals is up to 70% and the material achieves a
flexural strength of 400 MPa (74).
b. Three-stage Process
This process is used to obtain millable blocks of lithium disilicate. After the first
stage, as described above, the glass is introduced in the furnace once again (690–710°C)
for 10 to 30 minutes to form lithium metasilicate crystals (second stage), and then the
glass is left to cool down at room temperature. In this state the material is partially
crystallized and is formed by 40% lithium metasilicate crystals. At this state the crystals
size is 0.2-1.0 µm and the crystals have a platelet shape, giving the material a flexural
strength of 130 MPa. This is the stage (blue state) where the material can be easily milled.
Once the restoration is milled, it is introduced into a furnace with vacuum at 850ºC for
20-25 minutes (third stage), where the material composition changes from lithium
metasilicate crystals to lithium disilicate crystals and a small amount of lithium
orthophosphate crystals. This happens because of the interaction of the lithium
metasilicate crystals with the surrounding glass silica which forms small rod-like and
interlocked 1.5μm to 5µm -lithium disilicate crystals with a needle shape in a volume
fraction of up to 70%. This increases the flexural strength of the material up to 360 MPa.
Also, in this stage a 0,2% shrinkage of the material occurs, which is already taken under
consideration by the design software (74–77).
c. Staining and Glazing
Lithium disilicate is a monolithic material, this means that it comes in a single shade.
That is why the concept of staining the ceramic was introduced (78). Usually, after milling
or pressing, most of the restorations require the use of stains and glazes to achieve a
gradient of different shades that will better mimic the appearance of the natural teeth (79).
13
To characterize a restoration there is a need of minimum two firing cycles, one for the
colorants and one for the glaze (80).
1.3 Optical changes
In dental ceramics, the translucency and optical properties can be influenced by
various factors, like the chemical composition, the microstructure, the crystalline phase
distribution and refractive index, the shape and size of the particles, the fabrication
procedures, the porosity, and the number of firings (81,82).
Lithium disilicate presents a lower translucency when the crystal content is high, and
the size of the crystals is smaller (83). When lithium disilicate is exposed to multiple or
repeated firings, different phenomenon occur that can change the shade and the
translucency of the materials, like a more compact interlocking of the crystals (84), an
increase in the crystal size (83), and the metal oxides can be affected by the firing
temperatures. Some metal oxides, when exposed to high temperatures can experience a
pigment breakdown affecting the final shade of the material (85,86). If the crystal size
increases, the translucency will increase, and the light scattering and the light reflectance
will decrease (87).
The final shade of the ceramic will also depend on the coloring agents that are used.
If during crystallization these ions remain in the glassy matrix (because they are too big
to enter quartz, mullite, or spinel structures) there will be little or no color change. Still,
some of these agents are able to replace regular octahedral and sometimes tetrahedral
sites in many crystal phases found in glass-ceramics generating dramatic color changes
(42).
1.3.1 Color Science and Translucency in Dentistry
When light encounters the tooth structure it can be transmitted, diffused or
absorbed, therefore any restoration that is placed in the mouth should not only have the
same shade as the patient´s tooth, but also the same optical properties (88–91). Teeth and
restorations possess many optical properties, like opalescence, translucency, and
refractive index.
Opalescence is a property, where the shorter wavelengths of visible light spectrum
scatters, giving a material a bluish appearance under reflected light, and an orange-brown
appearance under transmitted light (92).
14
Translucency is a property that allows the light to pass through, but it scatters the
light in a way that does not allow objects to be seen clearly through the material; it is
considered to be a state between transparency and opacity (93).
Refractive index measures the bending of a ray of light when passing from one medium
into another (94).
Transparent objects allow the light to pass tough with minimal change, translucent
objects absorb transmit and scatter light, while opaque materials absorb and reflect light
(95).
All these properties influence on the final shade of the teeth or restoration. In case
of restorations, at the end, the shade will be the determinant factor on the outcome of any
restorative treatment.
a. Color Systems
Color systems are a way to graphically organize all colors in a quantitative way.
This organization allows a more accurate color match in industry, art, and science. In the
twentieth century the first color system was developed by Albert Henry Munsell (Munsell
Color System) and it is still used nowadays (96). In this system every color can be
described in three variables hue, chroma and value. The hue describes the name of the
color (red, blue, green), the chroma described the purity of the color, and the value
describes the darkness or lightness of the color. Each color is labeled alpha numerically
with a number for the chroma, a number for the value and a letter for the hue (96).
Later in the 1930’s the CIE (Commission Internationale d’Eclairage) was given the
authorization to create a standard color table that will allow objectiveness and precision
in color matching. They based their color table on the theory described in 1985 by the
physicist James C. Maxwell. This physicist demonstrated that any color can be obtained
by mixing the three spectral colors red, green, and blue (RGB). The CIE converted the
RGB values into the three new tristimulus values x, y and z and developed the CIE 1931
system (97).
In 1976, a new system was proposed by the CIE, the CIE L*a*b* where L* stands
for lightness, a* for the green–red coordinate and b* for the blue– yellow coordinate
Another illustration of the CIE L*a*b system is the so-called L*C*h parameters. In this
system the distribution of the colors of the L*a*b color space remains the same; the
difference remains in how the location of the color in the color space is calculated. In the
L*a*b system a color location is defined by the distances on the coordinates L, a and b.
15
On the other hand, in the L*C*h system a color location is defined by the distance on the
coordinate L (lightness), with the degree C (chroma,) and the angle h (hue).
To objectively determine the difference between two colors, the ΔE formula was
developed (Equation 1). “Δ” stands for difference and “E” is the initial of “Empfindung”
(German for sensation/perception) (97).
∆𝐸 𝑓𝑜𝑟𝑚𝑢𝑙𝑎 = -(∆𝐿
!
+∆𝑎
!
+∆𝑏
!
)
Equation 1. ∆𝐸 𝑓𝑜𝑟𝑚𝑢𝑙𝑎
This formula has evolved over the years, in 1994 the CIE94 was developed with
its new formula ΔE*94 Equation 2. With CIE94 the weighting function for lightness (SL)
was kept as 1.0. But they did not consider the rotation term or the correction for neutral
colors. During the development of CIE94 an attempt was made to add a hue-angle-
dependent function for hue differences and a lightness- difference correction, but the
available experimental data were too noisy in the case of the former and varied too much
from experiment to experiment in the latter (98).
∆𝐸∗
"#
= 4(
∆𝐿∗
𝑘
$
𝑆
$
)
!
+(
∆𝐶 ∗
%&
𝑘
'
𝑆
'
)
!
+(
∆𝐻∗
%&
𝑘
(
𝑆
(
)
!
Equation 2. ∆E*94 formula
To correct the previous errors, in 2001 a new color system CIEDE200 with a new
ΔE was developed. This new formula is more sophisticated and computationally involved
than its predecessors (99). Research has found that this formula gives a better evaluation
of the difference in color, providing better indicator of human acceptability and
perceptibility of color differences between teeth (100,101). This formula and all its
components will be explained further in the research.
When using this formula, if the ΔE00 is higher than 1 (ΔE00>1) it means that 50% of the
human observers can tell the color difference (102). If the ΔE00 is higher than 2, all
observers can see the color difference (103). A mean ΔE00 of 3.7 is acceptable in the
mouth since the light incidence is limited, and a ΔE00 of less than 2 is considered excellent
esthetics (104). To calculate any ΔE, L*, a* and b* values need to be measured using
different devices.
16
b. Measuring devices
In the last 20 years, dentistry had experienced the development of technologies
dedicated to the communication verification and analysis of shade (105).
Shade matching has always represented a challenge in dentistry, a way to objectively
quantify color has been the aim to replace selective visual shade selection (106).
There are several ways to determine the shade of teeth and restorations, a summary of
these methods is given in Table 3.
Shade Determination Methods
Methods Products Advantages Disadvantages
Visual
Vitapan Classical
Vitapan 3D-Master (VITA Zahnfabrik,
Bad Säckingen, Germany)
Affordable
Inconsistent among the
same manufacturers.
Difficult
communication
Spectrophotometers
Crystaleye (Olympus, Tokyo, Japan)
Vita Easyshade Compact (VITA
Zahnfabrik, Bad Säckingen, Germany)
Shade-X (X-Rite, Grandville, MI)
SpectroShade Micro (MHT Optic
Research, Niederhasli, Switzerland)
Accurate
Useful
Flexible
Expensive
Colorimeters ShadeVision (X-Rite, Grandville, MI) Accurate
Less accurate than
spectrophotometers
Digital Cameras
Canon (Canon, Tokyo, Japan)
Nikon (Nikon, Tokyo, Japan)
Sony (Sony, Tokyo, Japan)
Can be used for
other purposes
Require a degree of
subjective visual shade
matching
Intraoral scanners
Medit (MEDIT, Seoul, Korea)
3-Shape TRIOS (3Shape, Copenhagen K
Denmark)
iTero (Align Technology, San Jose, USA)
Primescan (Dentsply Sirona, York, USA)
Is not affected by
the light source or
by the clinician
experience
Less accurate than
spectrophotometers
Table 3 Shade Determination Methods (105,107,116,117,108–115)
b.1 Visual Method
This method involves the use of dental shade guides. A shade guide consists of
tooth color physical samples called shade tabs. The tabs are placed next to the tooth, and
the most similar tab to the tooth is selected and used for fabricating the restoration. The
accuracy and precision of the visual method depend on observer color matching
ability/experience, and light source (109,118,119).
17
b.2 Spectrophotometers
Are the most useful, flexible and accurate methods of shade determination (120).
These devices measure the amount of light energy that is reflected from an object at
intervals of 1–25 nm, and it goes over the whole light spectrum. (121,122). It is 33% more
accurate and obtains a more objective match in 93.3% of the cases compared to the visual
method. Its technology involves an optical radiation source, a dispersing light element, a
measuring optical system, a detector, and an element that transforms the obtained light
into a signal that can be analyzed (123). This devices have an integrated light and
therefore are not affected by the ambient light (120,124). There are two types of
spectrophotometers, one type measures the shade of an entire tooth and the other type has
an aperture of 3-5 mm diameter and only measures an area of the tooth (spot-
measurement) (125).
b.3 Colorimeters
These devices measure tristimulus values and filter light in, green, blue, and red
areas of the visible spectrum. A difference between spectrophotometers and colorimeters
is that the latter do not registering spectral reflectance, which makes them less accurate
than spectrophotometers (126).
b.4 Digital Cameras
Most of the images acquired by these devices are created by green, red, and blue
image information. These colors are combined in different ways to obtain broad array of
color. They are usually used in combination of a dental shade guide or a specific software
for color analysis (116). An example of a software is the ClearMatch which contains the
color database of industry-standard shade guides and compares them with the tooth color
(105). The accuracy/precision of these devices depends on flashes, settings and
calibrations, color adjustments, object features, and ambient lighting (126).
b.5 Intraoral Scanners
Even though they are used for digital impressions, some of them have developed a
new tool for shade matching. After the scanning is done a software analyzed the tooth
and determines the shade according to VITA shades rather than color parameters (117).
Still these technology is still developing and has shown to be less accurate than
spectrophotometers, although this technology is very promising (127).
18
1.4 Color and Translucency Research
Because of the great importance that dental esthetics has achieved in the past years,
there are many published studies that evaluate methods of measuring teeth shade and
translucency, the shade and translucency of restorations made of different materials and
the stability of the shade and translucency of these materials (125,128–130). Some of
these studies have focused on IPS e.max’s (milled and pressed) color and translucency
stability after multiple firings and have compare it to different materials (104,131–133).
Still to the date there are no studies that have evaluated the color and translucency stability
of these new lithium disilicate materials after multiple firings.
19
2. Aim
As stated above lithium disilicate is a material that is very commonly used in dentistry
because of its properties and advantages. Since there has been new lithium disilicate
products that have been introduced into the market, and since there are no studies that
evaluate the color stability of these materials after multiple firings, the aim of this in vitro
study is to assess the effect of multiple firings on the color and translucency of different
lithium disilicate CAD-CAM materials with thicknesses of 0.5 mm and 1 mm.
3. Null Hypothesis
3.1 Color Change
1. Multiple firings do not affect the color of the different lithium disilicate CAD-CAM
materials.
2. The thickness of the material does not affect the color of the different lithium
disilicate CAD-CAM specimens after multiple firings.
3. Different lithium disilicate CAD-CAM materials do not affect the color of the
specimens after multiple firings.
3.2 Translucency Parameter
4. Multiple firings do not affect the translucency of the different lithium disilicate CAD-
CAM materials.
5. The thickness of the material does not affect the translucency of the different lithium
disilicate CAD-CAM specimens after multiple firings.
6. Different lithium disilicate CAD-CAM materials do not affect the translucency of
the specimens after multiple firings.
20
4. Materials and Methods
4.1 Materials
A total of 160 specimens (length 14.00 mm x width 12.00 mm x with thicknesses
of 0.5 mm and 1.0 mm) of 4 different lithium-disilicate reinforced glass ceramic blocks
(Figure 3) were divided into 8 groups (n=15) (
Table 4).
The studied materials were:
• IPS e.max CAD HT (EX; IPS e.max CAD, Ivoclar Vivadent, Schaan, Liechtenstein),
• n!ce HT (NC; Straumann, Freiburg, Germany),
• Initial LiSi Block HT (LS; GC, Tokyo, Japan),
• Amber Mill (AM, HASSBIO, Kangreung, Korea)
Figure 3. Studied Materials
21
Table 4. Study groups based on material, thickness and number of firings
22
4.2 Specimen Preparation
The CAD-CAM blocks were sectioned into 160 rectangular shaped specimens
(14.00 mm x 12.00 mm) with a precision saw (IsoMet 1000, Buehler, Lake Buff, IL,
USA. Figure 4) equipped with a diamond blade (102 mm diameter, 0.3 mm thickness;
IsoMet Blade 15LCA, Buehler, Lake Buff, IL, USA. Figure 5) at a speed of
approximately 900 RPM under continuous cooling with distilled water. The blocks were
sectioned with a thickness of 0.5 mm and 1.0 mm (Figure 6).
Figure 4. Precision Saw
23
Figure 5. Diamond Blade
Figure 6. Sliced Specimens
The final thickness was achieved by manually polishing (MXBAOHENG Mini
Belt Sander 1.2-Inch by 15-Inch, Electric Mini Disc Sander 6-Inch, Small Sanding Belt
Machine for Wood Crafts Metal Stone Grinding 100W 8000RPM, Model A.Figure 7 )
one surface of the samples with 320 grit silicone paper (CarbiMet Abrasive Sheet, 600,
SiC, Buehler, Lake Buff, IL, USA). The standardization of the samples was achieved by
manually polishing one surface of the samples with 400, 600, 800, and 1200 grit silicone
paper (CarbiMet Abrasive Sheet, 600, SiC, Buehler, Lake Buff, IL, USA). After
polishing, the thickness was verified with a digital caliper (Digimatic Caliper CD-4”CSX,
Mitutoyo digital caliper; Mitutoyo Corp, Kawasaki, Japan. Figure 8) with a 0.001-mm
accuracy.
24
Figure 7. Polishing Machine
Figure 8. Digital Caliper
The non-polished surfaces were marked with the specimen number in the upper
right corner with a 0.7 mm diameter tapered micro flame diamond bur (#856.31.014
Medium Round-End Taper Diamond, Brasseler, Savannah, GA USA) using a high-speed
handpiece (Bien Air Classic CA 1:5L Highspeed Handpiece 1600386-001, Bien-Air
Dental, Le Noirmont, Switzerland) under continuous water irrigation at 200,000 rpm,
with a 1:5 ratio and a torque of 0.70Ncm. The burs were replaced every 15 samples.
All specimens were thoroughly cleaned by immersion in distilled water (Arrowhead
Mountain Spring Water, BlueTriton, San Bernardino, CA, USA) using an ultrasonic bath
(Ultrasonic Cleaning Systems, Quantrex, Kearny, NJ, USA) for 10 min. The specimens
were air dried and kept in plastic containers (DUOFIRE Plastic Organizer Container
Storage Box Adjustable Divider Removable Grid Compartment for Jewelry Beads
Earring Container Tool Fishing Hook Small Accessories(15 grids) White, Amazon,
25
Bellevue, WA, USA). The containers were marked with labels, according to the
specimen’s thickness and material brand, for easier classification.
4.3 Specimen Firing
Usually, two firings are necessary for EX and AM glass-ceramic materials
according to manufacturers’ recommendations, with one for crystallization and another
for staining and glaze (133). This is required because EX and AM are sold and milled as
lithium metasilicate, which is in a pre-crystallized sate (purple shade) for EX and an
amber shade for AM (Figure 9, Figure 10). A crystallization firing at a certain temperature
is necessary to transform this material into lithium disilicate. Once the crystallization
firing has finished, the EX and AM restorations will achieve its actual shade (labside
systems) (61,76,77,134,135). AM lithium disilicate blocks provide the possibility of
achieving different translucency depending on the firing temperature, at higher
temperatures, there is a decrease in the translucency(135). NC and LS can be used without
the need of firings (chairside systems). For these materials firing is optional if additional
characterizations are needed (62,63).
In this study, the specimens of each ceramic were divided into 6 subgroups
according to the number of firing cycles: B (Baseline- 0 firings), 1F (1 firing), 2F (2
firings), 3F (3 firings), 4F (4 firings) and 5F (5 firings). All the specimens were fired
according to the temperature recommendations given by the manufacturers
Table 5 (61–64,135), using a sintering furnace (Programat CS3 Furnace, Ivoclar
Vivadent, Schaan, Liechtenstein) that was previously calibrated. The EX and AM-
specimens were subjected to a crystallization firing before the baseline. After the EX and
AM-specimens were crystalized, all groups were subjected to a stain and glaze sintering.
It is important to mention that no glaze or stains were used in this study because they
might interfere with the shade and the translucency of the specimens.
26
Figure 9. IPS E-max specimens before and after crystallization firing by end user
Figure 10. Amber Mill specimen before and after crystallization firing by end user
27
Table 5. Firing Parameters (EX: IPS e.max Cad, LS: The Initial LiSi Block, NC: n!ce, AM: Amber Mill
28
A total of ten specimens at a time were placed on the firing plate. The firing plate
was placed inside the furnace using a Rochester Pean Straight Hemostat Forceps (Ivoclar
Vivadent, Schaan, Liechtenstein). Depending on the material, a specific firing cycle, that
follows the manufacturer’s recommendations, was selected. For the AM specimens the
instructions to achieve a high translucency (HT) were followed. Once each firing cycle
was finished, the hemostat was used to remove the firing plate from the firing plate holder,
and it was placed on a cooling tray for 15 minutes while the furnace head was kept closed.
Then, using the hemostat the firing plate was placed on a heat resistant flat surface away
from the furnace for an additional 15-minute cooling.
4.4 Color and Translucency Analysis
Fifteen minutes after each firing cycle, color measurements of the CIE L*a*b*
data were performed by measuring at 3 predetermined points (Figure 11), 3 times on
white and 3 times on black backgrounds (JJC 10" x 8" PVC White Balance Card Set,
Amazon, Bellevue, WA, USA, Figure 12) by using an imaging spectrophotometer
(Crystaleye Spectrophotometer®, Olympus, Tokyo, Japan). The spectrophotometer was
calibrated prior to the color measurement. After the initial calibration, the device emits a
sound each time calibration is needed. Calibration is accomplished by using a reference
plate installed at the edge of the cradle. Once the spectrophotometer was calibrated, a
contact cap was attached on top of the spectrophotometer, and the device was placed over
the center of the specimen’s surface to capture the image. All measurements were made
by the same investigator in the same location and under the same brightness conditions.
Figure 11. Predetermined Measuring Points
29
Figure 12. Color Measurement on White and Black Background
The images were transferred into the corresponding computer software
(Crystaleye® Application Software, Olympus, Tokyo, Japan) on a laptop (VAIO
Computer, Sony Electronics, Minato City, Tokyo, Japan). The outline of each specimen
was defined (Figure 13), the color analysis of each specimen was performed in the
software to obtain the L*, a*, b*, value (Figure 14) and the data was entered into an excel
spreadsheet (Excel; Microsoft, Redmond, WA, USA).
Figure 13. Outline Definition
30
Figure 14. Color Analysis
4.4.1 Color Analysis
The CIEDE2000 color difference (ΔE00) was calculated by applying the
CIEDE2000 color difference formula (136):
∆𝐸
))
= [(
∆𝐿
*
𝐾
$
𝑆
$
)
!
+(
∆𝐶
*
𝐾
'
𝑆
'
)
!
+(
∆𝐻
*
𝐾
(
𝑆
(
)
!
+𝑅
+
<
∆𝐶
*
𝐾
'
𝑆
'
=<
∆𝐻
*
𝐾
(
𝑆
(
=]
,/!
Equation 3. CIEDE2000 Color Difference Formula
To calculate the ΔL’ values, the following formulas were applied:
∆𝐿
*
= 𝐿′
,
−𝐿′
)
Equation 4. ∆L' Differences in lightness
𝐿
*
= 𝐿
∗
Equation 5. L’
To calculate the ΔC’ the following formulas were applied:
∆𝐶
*
= 𝐶′
,
−𝐶′
)
Equation 6. ∆C’ Differences in chroma
𝐶
*
= (𝑎′
!
+𝑏′
!
)
,/!
Equation 7. C'
31
𝑎
*
= (1+𝐺)𝑎
∗
Equation 8. a'
𝑏
*
= 𝑏
∗
Equation 9. b'
The L* coordinate is a measure of the lightness-darkness of the specimen, and it
is located on the Z axis of the CIE L*a*b* color space. The greater the L* is, the lighter
the specimen. The values of L extend between 0 for black and 100 for white (97). The a*
coordinate is a measure of the chroma along the X axis of the CIE L*a*b* color space. A
positive a* relates to the amount of redness, and a negative a* relates to greenness of a
specimen. The b* coordinate is a measure of the chroma along the Y axis of the CIE
L*a*b* color space. A positive b* relates to the amount of yellowness, while a negative
b* relates to the blueness of the specimen (97,137). The subscript “0” is the reference
specimen (baseline) and the subscript “1” is the tested specimen (after firing).
ΔL’, ΔC’, ΔH’ are the differences in lightness, chroma, and hue, respectively (136).
𝐺 = 0,5F1−4
(C
∗
ab)
/
(C
∗
ab)
/
+25
/
K
Equation 10. G
C
∗
ab is the arithmetic mean of the C*ab values for the two samples of the color difference
pair (136).
To calculate the ΔH’ the following formulas were applied:
∆𝐻
*
= 2(𝐶
*
)
𝐶′
)
)
,/!
sin(∆ℎ′ 2 ⁄ )
Equation 11. ∆H' Differences in hue
∆ℎ = 0°
Equation 12. ∆h Hue angle difference
The weighting functions (SL, SC, and SH) adjust the total color difference for
variation in the location of the color difference pair in L*, a*, b* coordinates (136), and
was calculated using the following formulas:
32
𝑆
$
= 1+(
0.015SL
*
−50U
!
V
20+SL
*
−50U
!
Equation 13. SL
𝑆
'
= 1+0,045 C
*
Equation 14. Sc
𝑆
(
= 1+0,015 C
*
𝑇
Equation 15. SH
𝑇 = 1−0,17 cos,h
!
−30°0+0,24cos,2h
!
0+0,32cos,3h
!
+6°0+0,20cos(4h
!
−63°)
Equation 16. T
The L
*
, C
*
and h
!
values are the arithmetic means of the corresponding values of
the colour-difference pair.
The parametric factors (KL, KC, and KH) are correction terms for experimental
conditions. For calculation, all parametric factors were set to 1 (KL = KC = KH = 1) (136).
The modified hue h’ has the geometric interpretation in the two dimensional a’–b* plane
as the angular position of the point (a’, b*) measured from the positive a’ axis (99).
Finally, a rotation function (RT) accounted for the interaction between chroma and hue
differences in the blue region (136), and it was calculated with the following formulas:
𝑅
+
= sin(2∆𝜃)𝑅
'
Equation 17. RT
∆𝜃 = 30°exp^−_(ℎ
*
−275°)/25°b
!
c
Equation 18. ∆θ
𝑅
'
= 2
4
S𝐶
*
U
/
(𝐶
*
)
!
+25
/
Equation 19. Rc (136,138)
Color differences were evaluated in accordance to recent data on 50:50%
perceptibility (PT = 0.81 ΔE00units) and 50:50% acceptability (AT = 1.77 ΔE00 units)
color thresholds (139).
33
The color difference from the first firing (1F) to the baseline (B) was calculated
as ∆E1; the color difference from the second firing (2F) to the baseline (B) was calculated
as ∆E2; the color difference from the third firing (3F) to the baseline (B) was calculated
as ∆E3, the color difference from the fourth firing (4F) to the baseline (B) was calculated
as ∆E4, and the color difference from the fifth firing (5F) to the baseline (B) was
calculated as ∆E5 (Figure 15).
Figure 15. Color Difference Calculation
4.4.2 Translucency Analysis
The translucency level of each specimen was calculated by using the translucency
parameter (TP) in the following equation (32,81,140,141).
𝑇𝑃 = ([𝐿
∗
0
−𝐿
∗
1
]
!
+[𝑎
∗
0
−𝑎
∗
1
]
!
+[𝑏
∗
0
−𝑏
∗
1
]
!
)
,
!
Equation 20. Translucency Parameter
W and B are color coordinates of the specimens on the white and black
backgrounds.
Higher TP values represent higher translucency (131). The translucency that was
calculated during the baseline was called TPB, the translucency that was calculated after
the first firing was TP1, the translucency that was calculated after the second firing was
TP2, the translucency that was calculated after the third firing was ∆T3, the translucency
34
that was calculated after the fourth firing was TP4. Finally, the translucency that was
calculated after the fifth firing was TP5 (Figure 16).
Figure 16. Translucency Calculation
4.5 Statistical Analysis
Collected data were manually transcribed to Microsoft Excel (Office 365 for Mac,
Microsoft, Redmond, WA, USA). The ΔE and TP formulas were entered in Microsoft
Excel and the values were calculated. The data was exported and were analyzed using the
Statistical Package for Social Sciences (SPSS Inc., Chicago, IL, USA, version 28 for
Mac). The ∆E and the TP were analyzed separately. The normality of the data was
calculated using the Kolmogorov Smirnov and Shapiro Wilk tests (p<0.05). Due to the
lack of heterogeneity of the variances (p<0.05), the statistical analysis was applied using
non- parametric tests. The Mann-Whitney U test was applied when comparisons between
two groups were done and the Kruskall-Wallis test was used when more than two groups
were compared. Finally, pairwise Mann-Whitney comparisons were applied to identify
where the difference relied, and the Bonferroni correction was applied by multiplying the
obtained p-value by the number of comparisons while maintaining the level of
significance at ⍺=0.05.
35
5. Results
The Kolmogorov-Smirnov and the Shapiro-Wilk tests showed that generally, the data
were not normally distributed (p<0.05). Therefore, applying parametric analysis was not
possible. The Mann-Whitney U test was applied when comparisons between two groups
were done and the Kruskall-Wallis test was used when more than two groups were
compared (⍺=0.05). Finally, pairwise Mann-Whitney comparisons were used to identify
where the difference relied, and the Bonferroni correction was applied. For this correction
the p-value was adjusted and the ⍺ was kept constant (⍺=0.05), to do so the obtained p-
value was multiplied by the number of comparisons.
The results showed that the higher the ΔE values, the higher and more noticeable the
color change. The higher the TP values, the more translucent the specimen.
5.1 Color Change Analysis
5.1.1 Overall Comparisons
Visually, all materials showed varying degrees of non-homogenous distribution
of shade and translucency within each specimen. With the naked eye, this was very
obvious in the AM specimens, which presented a spotted pattern throughout the entire
surface of the specimen. Also, LS appeared to be more opaque towards the margins of all
specimens.
The differences in color and translucencies within the EX and NC specimens
could only be observed under higher magnification (Figure 17).
36
Figure 17. Lithium Disilicate Materials after multiple firings (B: Baseline; 1F: first firing; 2F: second firing; 3F:
third firing; 4F: forth firing; 5F: fifth firing)
In the overall comparison the ΔE values ranged from 0.36 (EX 0.5 mm) to 6.86 (AM 1
mm). AM showed the highest color change in both thicknesses. The differences between
materials were significant (p<0.05). NC and LS where the only ones without a significant
difference. The two thicknesses did not present a significant difference. There was not a
significant difference between firings.
Material
EX
0.5 mm
EX
1 mm
NC
0.5 mm
NC
1 mm
LS
0.5 mm
LS
1 mm
AM
0.5 mm
AM
1 mm
ΔE00
Mean 0.37 0.36 1.08 0.56 1.03 1.32 3.80 6.86
SD 0.27 0.18 0.49 0.17 0.28 0.55 2.22 4.15
Min 0.03 0.11 0.24 0.12 0.7 0.76 0.65 1.32
Max 1.60 0.87 2.23 1.11 2.10 3.08 10.17 18.19
Table 6. Overall materials mean, standard deviation, minimum and maximum values divided by thicknesses
37
Figure 18. Overall mean ΔE values of each material and thickness
Figure 19. Overall changes in ΔE between firings of 0.5 mm specimens
0.37
1.08
1.03
3.8
0.36
0.56
1.32
6.86
0
1
2
3
4
5
6
7
8
IPS e.max CAD n!ce Initial LiSi Block Amber Mill
Thickness
ΔE
0.5 mm 1 mm
0
1
2
3
4
5
6
7
B-1F B-2F B-3F B-4F B-5F
ΔE Firings
ΔE 0.5 mm
IPS e.max CAD n!ce Initial LiSi Block Amber Mill
38
Figure 20. Overall changes in ΔE between firings of 1 mm specimens
0
2
4
6
8
10
12
14
B-1F B-2F B-3F B-4F B-5F
ΔE Firings
ΔE 1 mm
IPS e.max CAD n!ce Initial LiSi Block Amber Mill
39
a. Overall comparison between different materials
Material
IPS e.max
CAD
n!ce
Initial LiSi
Block
Amber
Mill
ΔE00
Mean 0.37 0.82 1.18 5.33
SD 0.23 0.45 0.46 3.65
Min 0.21 0.12 0.7 0.65
Max 0.03 2.23 3.08 18.19
Table 7. Overall material mean, standard deviation, minimum and maximum values
When the materials were compared to each other, regardless of their thicknesses
and the number of firings, EX showed the lowest ΔE values (mean = 0.37), followed by
NC (mean = 0.82), and LS (1.18). The material with the highest ΔE was AM (mean =
5.33).
The Kruskal-Wallis test revealed that the difference between materials was
significant (p=0.000).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference between EX and NC (p=0.003), EX and LS (p=0.000), EX and AM
(p=0.000), NC and AM, (p=0.000) and LS and AM (p=0.000). There was not a significant
difference between NC and LS (p=0.159).
Pairwise Comparisons of Material
Adj. Sig.
*
IPS e.max CAD – n!ce 0.003
IPS e.max CAD – Initial LiSi Block 0.000
IPS e.max CAD – Amber Mill 0.000
n!ce – Initial LiSi Block 0.159
n!ce – Amber Mill 0.000
Initial LiSi Block – Amber Mill 0.000
Table 8. Overall pairwise comparison between materials
* Significance values have been adjusted by the Bonferroni correction for multiple tests.
40
Figure 21. Boxplot of ΔE for each material. *** (significant difference)
41
b. Overall comparison between different thicknesses
Thickness
0.5 mm 1 mm
ΔE00
Mean 1.57 2.28
SD 1.75 3.39
Min 0.03 0.11
Max 10.17 18.19
Table 9. Thicknesses mean, standard deviation, minimum and maximum values
When the thicknesses were compared to each other, regardless of the material and
the number of firings, the specimens with a thickness of 0.5 mm presented a lower ΔE
(mean = 1.57) than the specimens with a 1mm thickness (mean = 2,.8). Still the Mann-
Whitney U test revealed that this difference was not significant (p=0.912).
Figure 22. Boxplot of ΔE for each thickness.
42
c. Overall comparison between different firings
Firings
Mean SD Min Max
ΔE00
B-1F 1.41 1.42 0.06 5.64
B-2F 1.40 1.39 0.03 5.76
B-3F 1.61 1.76 0.16 7.88
B-4F 2.15 3.03 0.11 13.23
B-5F 3.05 4.36 0.17 18.19
Table 10. Firings mean, standard deviation, minimum and maximum values
When the firings were compared to each other, regardless of the material and the
thicknesses, the lowest ΔE was obtained between the B-2F (mean = 1.40) followed by B-
1F (mean = 1.41), B-3F (mean = 1.61), B-4F (mean = 2.15), and the highest ΔE was
obtained by B-5F (mean = 3.05).
The Kruskal-Wallis test revealed that the differences between firings were not significant
(p=0.58).
Figure 23. Boxplot of ΔE for each firing.
43
5.2.2 IPS e.max CAD Comparisons
a. IPS e.max CAD Thickness
Thickness IPS e.max CAD
0.5 mm 1 mm
ΔE00
Mean 0.37 0.36
SD 0.27 0.18
Min 0.03 0.11
Max 1.60 0.87
Table 11. IPS e.max CAD thicknesses’ mean, standard deviation, minimum and maximum values
The EX-specimens with a thickness of 1 mm showed a lower ΔE (mean = 0.36)
than the 0.5 mm thick specimens (mean = 0.37).
When EX thicknesses were compared to each other, the Mann- Whitney U test revealed
that the difference between thicknesses was not significant (p=0.870).
Figure 24. Boxplot of ΔE for each IPS e.max CAD thickness.
44
Figure 25. IPS e.max CAD specimens after multiple firings
b. IPS e.max CAD 0.5 mm Firings
Firings IPS e.max CAD 0.5 mm
Mean SD Min Max
ΔE00
B-1F 0.29 0.22 0.06 0.77
B-2F 0.32 0.29 0.03 1.21
B-3F 0.39 0.21 0.17 1.02
B-4F 0.36 0.15 0.11 0.74
B-5F 0.51 0.39 0.25 1.6
Table 12. IPS e.max CAD 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the EX 0.5 mm firings were compared to each other, B-1F showed the
lowest ΔE (mean = 0.29) followed by B-2F (mean = 0.32), B-4F (mean = 0.36), and B-
3F (mean = 0.39). B-5F showed the highest ΔE (mean = 0.51).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p=0.046). However, in the pairwise Mann-Whitney comparisons once the
Bonferroni correction was applied the results showed that there was not a significant
difference between the groups.
45
Pairwise Comparisons of Material
Material Thickness Firings Adj. Sig.
*
IPS e.max CAD 0.5 mm
B-1F-B-2F 1.000
B-1F-B-3F 0.844
B-1F-B-4F 0.595
B-1F-B-5F 0.138
B-2F-B-3F 1.000
B-2F-B-4F 0.859
B-2F-B-5F 0.217
B-3F-B-4F 1.000
B-3F-B-5F 1.000
B-4F-B-5F 1.000
Table 13. Pairwise comparison between firings of EX 0.5 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
Figure 26. Changes in ΔE between firings of 0.5 mm IPS e.max CAD specimens
0
0,1
0,2
0,3
0,4
0,5
0,6
B-1F B-2F B-3F B-4F B-5F
IPS e.max CAD 0.5 mm
46
Figure 27. IPS e.max CAD 0.5 mm specimens after multiple firings
c. IPS e.max CAD 1 mm Firings
Firings IPS e.max CAD 1mm
Mean SD Min Max
ΔE00
B-1F 0.27 0.15 0.11 0.64
B-2F 0.29 0.14 0.17 0.65
B-3F 0.39 0.18 0.16 0.76
B-4F 0.39 0.17 0.22 0.76
B-5F 0.47 0.19 0.17 0.87
Table 14. IPS e.max CAD 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the EX 1 mm firings were compared to each other, B-1F showed the lowest
ΔE (mean = 0.27) followed by B-2F (mean = 0.29). B-3F and B-4F presented the same
ΔE values (mean = 0.39), and B-5F showed the highest ΔE (mean = 0.47).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p=0.005).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the EX 1mm specimens between B-1F and B-5F (p=0.013).
47
Pairwise Comparisons of Material
Material Thickness Firings Adj. Sig.
*
IPS e.max CAD 1 mm
B-1F-B-2F 1.000
B-1F-B-3F 0.270
B-1F-B-4F 0.114
B-1F-B-5F 0.013
B-2F-B-3F 1.000
B-2F-B-4F 0.510
B-2F-B-5F 0.081
B-3F-B-4F 1.000
B-3F-B-5F 1.000
B-4F-B-5F 1.000
Table 15. Pairwise comparison between firings of EX 1 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
Figure 28. Changes in ΔE between firings of 1 mm IPS e.max CAD specimens
Figure 29. IPS e.max CAD 1 mm specimens after multiple firings
0
0,1
0,2
0,3
0,4
0,5
0,6
B-1F B-2F B-3F B-4F B-5F
IPS e.max CAD 1 mm
48
5.2.3 n!ce Comparisons
a. n!ce Thickness
Thickness n!ce
0.5 mm 1 mm
ΔE00
Mean 1.08 0.56
SD 0.49 0.17
Min 0.24 0.12
Max 2.23 1.11
Table 16. n!ce thicknesses’ mean, standard deviation, minimum and maximum values
When NC thicknesses were compared to each other, the ΔE of the 0.5 mm
specimens was higher (mean = 1.08) than the ΔE of the 1 mm specimens (mean =0.56)
The Mann- Whitney U test revealed that the difference between thicknesses was
significant (p<0.001).
Figure 30. Boxplot of ΔE for n!ce thicknesses. *** (significant difference)
49
Figure 31. n!ce specimens after multiple firings
b. n!ce 0.5 mm Firings
Firings n!ce 0.5 mm
Mean SD Min Max
ΔE00
B-1F 0.81 0.44 0.34 1.94
B-2F 1.05 0.49 0.52 2.21
B-3F 1.07 0.51 0.24 2.17
B-4F 1.22 0.51 0.53 2.23
B-5F 1.24 0.46 0.44 2.23
Table 17. n!ce 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the NC 0.5 mm firings were compared to each other, B-1F showed the
lowest ΔE (mean = 0.81) followed by B-2F (p= 1.05), B-3F (mean = 1.07), B-4F (mean
= 1.22). B-5F showed the highest ΔE (mean = 1.24).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p=0.057).
Figure 32. Changes in ΔE between firings of 0.5 mm n!ce specimens
0
0,2
0,4
0,6
0,8
1
1,2
1,4
B-1F B-2F B-3F B-4F B-5F
n!ce 0.5 mm
50
Figure 33. n!ce 0.5 mm specimens after multiple firings
c. n!ce 1 mm Firings
Firings n!ce 1mm
Mean SD Min Max
ΔE00
B-1F 0.48 0.32 0.12 1.42
B-2F 0.55 0.16 0.37 0.92
B-3F 0.62 0.21 0.42 1.25
B-4F 0.65 0.36 0.39 1.91
B-5F 0.71 0.26 0.44 1.40
Table 18. n!ce 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the NC 1 mm firings were compared to each other, B-1F showed the lowest
ΔE (mean = 0.48) followed by B-2F (mean = 0.55), B-3F (mean = 0.62), and B-4F (mean
= 0.65). B-5F showed the highest ΔE (mean = 0.71).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p=0.003).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the NC 1mm specimens between B-1F and B-5F (p=0.002).
51
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
n!ce 1 mm
B-1F-B-2F 0.890
B-1F-B-3F 0.063
B-1F-B-4F 0.092
B-1F-B-5F 0.002
B-2F-B-3F 1.000
B-2F-B-4F 1.000
B-2F-B-5F 0.385
B-3F-B-5F 1.000
B-4F-B-3F 1.000
B-4F-B-5F 1.000
Table 19. Pairwise comparison between firings of NC 1 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
Figure 34. Changes in ΔE between firings of 1 mm n!ce specimens
Figure 35. n!ce 1 mm specimens after multiple firings
0
0,2
0,4
0,6
0,8
1
1,2
1,4
B-1F B-2F B-3F B-4F B-5F
n!ce 1 mm
52
5.2.4 Initial LiSi Block Comparisons
a. Initial LiSi Block Thickness
Thickness Initial LiSi Block
0.5 mm 1 mm
ΔE00
Mean 1.03 1.32
SD 0.28 0.55
Min 0.70 0.76
Max 2.10 3.08
Table 20. Initial LiSi Block thicknesses’ mean, standard deviation, minimum and maximum values
When LS thicknesses were compared to each other, the ΔE of the 0.5 mm thick
specimens was lower (mean = 1.03) than the 1 mm thick specimens (mean = 1.32).
The Mann- Whitney U test revealed that the difference between thicknesses was
significant (p=0.021).
Figure 36. Boxplot of ΔE for Initial LiSi Block thicknesses. *** (significant difference)
Figure 37. Initial LiSi Block specimens after multiple firings
53
b. Initial LiSi Block 0.5 mm Firings
Firings Initial LiSi Block 0.5 mm
Mean SD Min Max
ΔE00
B-1F 0.97 0.30 0.70 1.59
B-2F 1.07 0.35 0.80 2.10
B-3F 1.10 0.32 0.78 2.04
B-4F 0.93 0.15 0.73 1.20
B-5F 1.09 0.21 0.89 1.53
Table 21. Initial LiSi Block 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the LS 0.5 mm firings were compared to each other, B-4F showed the
lowest ΔE (mean = 0.93) followed by B-1F (mean= 0.97), B-2F (mean = 1.07), B-5F
(mean = 1.09). B-3F showed the highest ΔE (mean = 1.10).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p=0.111).
Figure 38. Changes in ΔE between firings of 0.5 mm Initial LiSi Block specimens
Figure 39. Initial LiSi Block 0.5 mm specimens after multiple firings
0,9
1
1,1
1,2
1,3
1,4
1,5
B-1F B-2F B-3F B-4F B-5F
Initial LiSi Block 0.5 mm
54
c. Initial LiSi Block 1 mm Firings
Firings Initial LiSi Block 1 mm
Mean SD Min Max
ΔE00
B-1F 1.26 0.60 0.76 2.97
B-2F 1.33 0.54 0.92 2.94
B-3F 1.36 0.61 0.82 3.02
B-4F 1.39 0.54 0.91 3.08
B-5F 1.28 0.51 0.81 2.70
Table 22. Initial LiSi Block 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the LS 1 mm firings were compared to each other, B-1F showed the lowest
ΔE (mean = 1.26) followed by B-5F (mean = 1.28), B-2F (mean = 1.33), B-3F (mean =
1.34). B-4F showed the highest ΔE (mean = 1.39).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p=0.262).
Figure 40. Changes in ΔE between firings of 1 mm Initial LiSi Block specimens
Figure 41. Initial LiSi Block 1 mm specimens after multiple firings
0,9
1
1,1
1,2
1,3
1,4
1,5
B-1F B-2F B-3F B-4F B-5F
Initial LiSi Block 1 mm
55
5.2.5 Amber Mill Comparisons
a. Amber Mill Thickness
Thickness Amber Mill
0.5 mm 1 mm
ΔE00
Mean 3.80 6.86
SD 2.22 4.15
Min 0.65 1.32
Max 10.17 18.19
Table 23. Amber Mill thicknesses’ mean, standard deviation, minimum and maximum values
The ΔE of the 0.5 mm thick specimens was lower (mean = 3.80) than the 1 mm
thick specimens (mean = 6.86).
When AM thicknesses were compared to each other, the Mann- Whitney U test
revealed that the difference between thicknesses was significant (p<0.001).
Figure 42. Boxplot of ΔE for Amber Mill thicknesses *** (significant difference)
56
Figure 43. Amber Mill specimens after multiple firings
b. Amber Mill 0.5 mm Firings
Firings Amber Mill 0.5 mm
Mean SD Min Max
ΔE00
B-1F 3.09 0.69 2.27 4.80
B-2F 3.97 1.36 1.47 5.76
B-3F 2.61 0.76 1.62 4.06
B-4F 3.03 2.21 0.65 6.91
B-5F 6.28 2.97 1.76 10.17
Table 24. Amber Mill 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the AM 0.5 mm firings were compared to each other, B-3F showed the
lowest ΔE (mean = 2.61) followed by B-4F (mean = 3.03), B-1F (mean = 3.09), B-2F
(mean = 3.91). B-5F showed the highest ΔE (mean = 6.28).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the AM 0.5 mm specimens between B-1F and B-5F (p=0.044),
B-3F and B-5F (p=0.001), and B-4F and B-5F (p=0.008).
57
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
Amber Mill 0.5 mm
B-1F-B-2F 1.000
B-1F-B-3F 1.000
B-1F-B-4F 1.000
B-1F-B-5F 0.044
B-2F-B-3F 0.138
B-2F-B-4F 0.540
B-2F-B-5F 1.000
B-3F-B-4F 1.000
B-3F-B-5F 0.001
B-4F-B-5F 0.008
Table 25. Pairwise comparison between firings of AM 0.5 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
Figure 44. Changes in ΔE between firings of 0.5 mm Amber Mill specimens
0
2
4
6
8
10
12
14
B-1F B-2F B-3F B-4F B-5F
Amber Mill 0.5 mm
58
Figure 45. Amber Mill 0.5 mm specimens after multiple firings
c. Amber Mill 1 mm Firings
Firings Amber Mill 1 mm
Mean SD Min Max
ΔE00
B-1F 4.17 0.62 3.21 5.64
B-2F 2.60 1.24 1.32 5.65
B-3F 5.38 1.90 2.89 7.88
B-4F 9.31 2.01 6.48 13.23
B-5F 12.83 2.70 9.48 18.19
Table 26. Amber Mill 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the AM 1 mm firings were compared to each other, B-2F showed the lowest
ΔE (mean = 2.60) followed by B-1F (mean = 4.17), B-3F (mean = 5.38), B-4F (mean =
9.31). B-5F showed the highest ΔE (mean = 12.83).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the AM 1 mm specimens between B-1F and B-4F (p=0.005), B-
1F and B-5F (p=0.000), B-2F and B-4F (=0.000), B-2F and B-5F (p=0.000) and B-3F
and B-5F (p=0.000).
59
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
Amber Mill 1 mm
B-1F-B-2F 0.583
B-1F-B-3F 1.000
B-1F-B-4F 0.005
B-1F-B-5F 0.000
B-2F-B-3F 0.079
B-2F-B-4F 0.000
B-2F-B-5F 0.000
B-3F-B-4F 0.063
B-3F-B-5F 0.000
B-4F-B-5F 1.000
Table 27. Pairwise comparison between firings of AM 1 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
Figure 46. Changes in ΔE between firings of 1 mm Amber Mill specimens
Figure 47. Amber Mill 1 mm specimens after multiple firing
0
2
4
6
8
10
12
14
B-1F B-2F B-3F B-4F B-5F
Amber Mill 1 mm
60
5.2 CIE L*a*b*
5.2.1 L* overall comparison
When the L* results approach 100, the value of the specimen increases,
and if the L* results are closer to 0 or negative results, the specimen has a low value.
In the overall comparison the L* values ranged from 48.97 (AM 0.5 mm) to 67.06
(NC 1 mm). AM showed the lowest L* values in both thicknesses. The differences
between materials were significant (p<0.001). EX and LS where the only ones without a
significant difference. The two thicknesses showed a significant difference. There was a
significant difference between firings.
Material
EX
0.5 mm
EX
1 mm
NC
0.5 mm
NC
1 mm
LS
0.5 mm
LS
1 mm
AM
0.5 mm
AM
1 mm
L*
Mean 58.97 64.97 63.02 67.06 59.50 64.16 48.97 58.66
SD 0.44 0.23 0.70 0.32 1.89 0.96 3.96 5.26
Min 58.11 64.06 61.27 66.24 56.01 62.35 40.31 49.56
Max 60.69 65.42 64.30 67.64 64.09 67.09 59.33 67.59
Table 28. Overall materials mean, standard deviation, minimum and maximum values of L*
Figure 48. Overall mean L* values of each material and thickness
58.97
63.02
59.50
48.97
64.97
67.06
64.16
58.66
0,00
10,00
20,00
30,00
40,00
50,00
60,00
70,00
80,00
IPS e.max CAD n!ce Initial LiSi Block Amber Mill
L*
0.5 mm 1 mm
61
Figure 49. Overall changes in L* between firings of 0.5 mm specimens
Figure 50. Overall changes in L* between firings of 1 mm specimens
56
57
58
59
60
61
62
63
64
B 1F 2F 3F 4F 5F
L* 0.5 mm
IPS e.max CAD n!ce Initial LiSi Block Amber Mill
62
63
64
65
66
67
68
B 1F 2F 3F 4F 5F
L* 1 mm
IPS e.max CAD n!ce Initial LiSi Block Amber Mill
62
b. L* overall comparison between different materials
Material
IPS e.max
CAD
n!ce
Initial LiSi
Block
Amber
Mill
L*
Mean 61.97 65.04 61.83 53.81
SD 3.03 2.10 2.77 6.72
Min 58.11 61.27 56.01 40.31
Max 65.42 67.64 67.09 67.59
Table 29. Overall material mean, standard deviation, minimum and maximum values
When the materials were compared to each other, regardless of their thicknesses
and the number of firings, AM showed the lowest L* values (mean = 53.81), followed
by LS (mean = 61.83), and EX (61.97). The material with the highest L* was NC (mean
= 65.04).
The Kruskal-Wallis test revealed that the difference between materials was
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference between EX and NC (p=0.041), NC and LS (p=0.015), AM and EX
(p=0.000), AM and NC, (p=0.000) and AM and LS (p=0.000). There was not a significant
difference between EX and LS (p=0.1000).
Pairwise Comparisons of Material
Adj. Sig.*
IPS e.max CAD-n!ce 0.041
IPS e.max CAD- Initial LiSi Block 1.000
n!ce -Initial LiSi Block 0.015
Amber Mill-IPS e.max CAD 0.000
Amber Mill-n!ce 0.000
Amber Mill-Initial LiSi Block 0.000
Table 30. Overall pairwise comparison between materials
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
63
Figure 51. Boxplot of L* for each material. *** (significant difference)
64
c. Overall comparison between different thicknesses
Thickness
0.5 mm 1 mm
L*
Mean 57.62 63.71
SD 5.69 4.10
Min 40.31 49.56
Max 64.30 67.64
Table 31. Thicknesses mean, standard deviation, minimum and maximum values
When the thicknesses were compared to each other, regardless of the material and
the number of firings, the specimens with a thickness of 0.5 mm presented a lower L*
(mean = 57.62) than the specimens with a 1mm thickness (mean = 63.71).
The Mann- Whitney U test revealed that this difference was significant (p<0.001).
Figure 52. Boxplot of L* for each thickness.
65
d. Overall comparison between different firings
Firings
Mean SD Min Max
L*
B 60.02 5.52 45.29 66.95
1F 59.45 6.84 42.06 67.45
2F 59.88 6.73 40.31 67.40
3F 60.76 5.76 43.37 67.39
4F 61.55 5.00 47.38 67.52
5F 62.32 4.22 51.73 67.64
Table 32. Firings mean, standard deviation, minimum and maximum values
When the firings were compared to each other, regardless of the material and the
thicknesses, the lowest L* was obtained by 1F (mean = 59.45) followed by 2F (mean =
59.88), B (mean = 60.02), 3F (mean = 60.76), 4F (mean = 61.55) and the highest L¨ was
obtained by 5F (mean = 62.32).
The Kruskal-Wallis test revealed that the differences between firings was
significant (p=0.005).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference between B and 5F (p=0.012).
Pairwise Comparisons of Firings
Adj. Sig.*
B-1F 1.000
B-2F 1.000
B-3F 1.000
B-4F 0.236
B-5F 0.012
Table 33. Overall pairwise comparison between firings
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
66
Figure 53. Boxplot of L* for each firing.
67
5.2.2 IPS e.max CAD Comparisons
a. IPS e.max CAD Thickness
Thickness IPS e.max CAD
0.5 mm 1 mm
L*
Mean 58.97 64.97
SD 0.44 0.23
Min 58.11 64.06
Max 60.69 65.42
Table 34. IPS e.max CAD thicknesses’ mean, standard deviation, minimum and maximum values
The EX-specimens with a thickness of 0.5 mm showed a lower L* (mean = 58.97)
than the 1 mm thick specimens (mean = 64.97).
When EX thicknesses were compared to each other, the Mann- Whitney U test
revealed that the difference between thicknesses was significant (p<0.001).
Figure 54. Boxplot of L* for each IPS e.max CAD thickness.
68
b. IPS e.max CAD 0.5 mm Firings
Firings IPS e.max CAD 0.5 mm
Mean SD Min Max
L*
B 58.96 0.36 58.38 59.51
1F 58.92 0.50 58.20 60.04
2F 59.04 0.45 58.16 59.69
3F 59.16 0.33 58.60 59.66
4F 58.81 0.30 58.28 58.19
5F 58.92 0.61 58.11 60.69
Table 35. IPS e.max CAD 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the EX 0.5 mm firings were compared to each other,4F showed the lowest
L* (mean = 58.81) followed by 1F (mean = 58.92), B and 5F (mean = 58.92), and 2F
(mean = 59.04). 3F showed the highest L* (mean = 59.16).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p=0.155).
Figure 55. Changes in L* between firings of 0.5 mm IPS e.max CAD specimens
58
59
60
61
62
63
64
65
66
B 1F 2F 3F 4F 5F
IPS e.max CAD 0.5 mm
69
c. IPS e.max CAD 1 mm Firings
Firings IPS e.max CAD 1 mm
Mean SD Min Max
L*
B 64.97 0.32 64.23 65.42
1F 64.90 0.19 64.52 65.20
2F 64.92 0.21 64.65 65.28
3F 64.94 0.29 64.06 65.30
4F 65.02 0.12 64.79 65.16
5F 65.05 0.19 64.54 65.31
Table 36. IPS e.max CAD 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the EX 1 mm firings were compared to each other, 1F showed the lowest
L* (mean = 64.90) followed by 2F (mean = 64.92), 3F (mean = 64.94), B (mean = 64.97),
4F (mean = 65.02), and 5F showed the highest L* (mean = 65.05).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p=0.243).
Figure 56. Changes in L* between firings of 1 mm IPS e.max CAD specimens
58
59
60
61
62
63
64
65
66
B 1F 2F 3F 4F 5F
IPS e.max CAD 1 mm
70
5.2.3 n!ce Comparisons
a. n!ce Thickness
Thickness n!ce
0.5 mm 1 mm
L*
Mean 63.02 67.06
SD 0.70 0.32
Min 61.27 66.24
Max 64.30 67.64
Table 37. n!ce thicknesses’ mean, standard deviation, minimum and maximum values
When NC thicknesses were compared to each other, the L* of the 1 mm specimens
was higher (mean = 67.06) than the L* of the 0.5 mm specimens (mean = 63.02).
The Mann- Whitney U test revealed that the difference between thicknesses was
significant (p<0.001).
Figure 57 .Boxplot of L* for n!ce thicknesses. *** (significant difference)
71
b. n!ce 0.5 mm Firings
Firings n!ce 0.5 mm
Mean SD Min Max
L*
B 62.26 0.58 61.35 63.21
1F 62.87 0.70 61.27 63.99
2F 63.20 0.57 61.89 64.13
3F 63.21 0.63 61.58 64.08
4F 63.31 0.58 61.97 64.30
5F 63.29 0.56 61.14 64.12
Table 38. n!ce 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the NC 0.5 mm firings were compared to each other, B showed the lowest
L* (mean = 62.26) followed by 1F (p= 62.87), 2F (mean = 63.20), 3F (mean = 63.21),
and 5F (mean = 63.29). 4F showed the highest L* (mean = 63.31).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the NC 0.5 mm specimens between B and 2F (p=0.008), B and
3F (P=0.004), B and 4F (p=0.001), and B and 5F (p=0.001).
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
n!ce 0.5 mm
B-1F 0.450
B-2F 0.008
B-3F 0.004
B-4F 0.001
B-5F 0.001
Table 39. Pairwise comparison between firings of NC 0.5 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
72
Figure 58. Changes in L* between firings of 0.5 mm n!ce specimens
c. n!ce 1 mm Firings
Firings n!ce 1 mm
Mean SD Min Max
L*
B 66.60 0.24 66.26 66.95
1F 67.08 0.26 66.65 67.45
2F 67.11 0.20 66.76 67.40
3F 67.12 0.29 66.24 67.39
4F 67.20 0.24 66.70 67.52
5F 67.27 0.22 66.84 67.64
Table 40. n!ce 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the NC 1 mm firings were compared to each other, B showed the lowest L*
(mean = 66.60) followed by 1F (mean = 67.08), 2F (mean = 67.11), 3F (mean = 67.12),
4F (mean = 67.20). 5F showed the highest L* (mean = 67.27).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p=0.003).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the NC 1mm specimens between B and 1F (p=0.017), B and 2F
(p=0.005), B and 3F (p= 0.002), B and 4F p= 0.000) and B-5F (p=0.000).
61
62
63
64
65
66
67
68
B 1F 2F 3F 4F 5F
n!ce 0.5 mm
73
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
n!ce 1 mm
B-1F 0.017
B-2F 0.005
B-3F 0.002
B-4F 0.000
B-5F 0.000
Table 41. Pairwise comparison between firings of NC 1 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
Figure 59. Changes in L* between firings of 1 mm n!ce specimens
61
62
63
64
65
66
67
68
B 1F 2F 3F 4F 5F
n!ce 1 mm
74
5.2.4 Initial LiSi Block Comparisons
a. Initial LiSi Block Thickness
Thickness Initial LiSi Block
0.5 mm 1 mm
L*
Mean 59.50 64.16
SD 1.89 0.96
Min 56.01 62.35
Max 64.09 67.09
Table 42. Initial LiSi Block thicknesses’ mean, standard deviation, minimum and maximum values
When LS thicknesses were compared to each other, the L* of the 0.5 mm thick
specimens was lower (mean = 59.50) than the 1 mm thick specimens (mean = 64.16).
The Mann- Whitney U test revealed that the difference between thicknesses was
significant (p<0.001).
Figure 60. Boxplot of L* for Initial LiSi Block thicknesses. *** (significant difference)
75
b. Initial LiSi Block 0.5 mm Firings
Firings Initial LiSi Block 0.5 mm
Mean SD Min Max
L*
B 59.19 1.84 56.07 62.34
1F 59.73 1.97 56.34 63.90
2F 59.86 1.94 56.80 64.09
3F 59.36 2.11 56.29 63.97
4F 59.40 1.79 56.01 62.39
5F 59.48 1.95 56.14 63.75
Table 43. Initial LiSi Block 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the LS 0.5 mm firings were compared to each other, B showed the lowest
L* (mean = 59.19) followed by 3F (mean = 59.36), 4F (mean = 59.40), 5F (mean = 59.48),
and 1F (mean = 59.73). 2F showed the highest L* (mean = 59.86).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p=0.843).
Figure 61. Changes in L* between firings of 0.5 mm Initial LiSi Block specimens
58
59
60
61
62
63
64
65
B 1F 2F 3F 4F 5F
Initial LiSi Block 0.5 mm
76
c. Initial LiSi Block 1 mm Firings
Firings Initial LiSi Block 1 mm
Mean SD Min Max
L*
B 63.82 0.92 62.35 66.15
1F 64.28 0.99 62.90 67.09
2F 64.34 1.05 62.42 67.05
3F 64.37 0.96 62.84 67.01
4F 64.06 0.86 62.62 65.90
5F 64.09 1.00 62.70 66.79
Table 44. Initial LiSi Block 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the LS 1 mm firings were compared to each other, B showed the lowest L*
(mean = 63.82) followed by 4F (mean = 64.06), 5F (mean = 64.09), 1F (mean = 64.28),
and 2F (mean = 64.34) and 3F showed the highest L* (mean = 64.37).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p=0.253).
Figure 62. Changes in L* between firings of 1 mm Initial LiSi Block specimens
58
59
60
61
62
63
64
65
B 1F 2F 3F 4F 5F
Initial LiSi Block 1 mm
77
5.2.5 Amber Mill Comparisons
a. Amber Mill Thickness
Thickness Amber Mill
0.5 mm 1 mm
L*
Mean 48.97 58.66
SD 3.96 5.26
Min 40.31 49.56
Max 59.33 67.59
Table 45. Amber Mill thicknesses’ mean, standard deviation, minimum and maximum values
The L* of the 0.5 mm thick specimens was lower (mean = 48.97) than the 1 mm
thick specimens (mean = 58.66).
When AM thicknesses were compared to each other, the Mann- Whitney U test
revealed that the difference between thicknesses was significant (p<0.001).
Figure 63. Boxplot of L* for Amber Mill thicknesses *** (significant difference)
b. Amber Mill 0.5 mm Firings
78
Firings Amber Mill 0.5 mm
Mean SD Min Max
L*
B 49.01 2.13 45.29 51.41
1F 46.23 2.47 42.06 48.56
2F 45.29 2.73 40.31 48.04
3F 47.88 2.73 43.37 51.65
4F 50.82 2.59 47.38 56.17
5F 54.57 2.51 51.73 59.33
Table 46. Amber Mill 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the AM 0.5 mm firings were compared to each other, 2F showed the lowest
L* (mean = 45.29) followed by 1F (mean 46.23), 3F (mean = 47.88), B (mean = 49.01),
and 4F (mean = 50.82). 5F showed the highest L* (mean = 54.57).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the AM 0.5 mm specimens between B and 5F (p=0.003).
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
Amber Mill 0.5 mm
B-1F 0.630
B-2F 0.067
B-3F 1.000
B-4F 1.000
B-5F 0.003
Table 47. Pairwise comparison between firings of AM 0.5 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
79
Figure 64. Changes in L* between firings of 0.5 mm Amber Mill specimens
c. Amber Mill 1 mm Firings
Firings Amber Mill 1 mm
Mean SD Min Max
L*
B 55.37 0.81 53.27 56.42
1F 51.62 0.97 49.56 53.08
2F 55.25 1.84 52.36 57.44
3F 60.06 1.66 57.97 62.25
4F 63.76 1.66 61.51 63.59
5F 65.89 1.44 63.99 67.59
Table 48. Amber Mill 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the AM 1 mm firings were compared to each other, 1F showed the lowest
L* (mean = 51.62) followed by 2F (mean = 55.25), B (mean = 55.37), 3F (mean = 60.06),
and 4F (mean = 63.76). 5F showed the highest L* (mean = 65.89).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the AM 1 mm specimens between B and 4F (p=0.000), and B
and 5F (p=0.000).
30
35
40
45
50
55
60
65
70
B 1F 2F 3F 4F 5F
Amber Mill 0.5 mm
80
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
Amber Mill 1 mm
B-1F 0.316
B-2F 1.000
B-3F 1.197
B-4F 0.000
B-5F 0.000
Table 49. Pairwise comparison between firings of AM 1 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
Figure 65. Changes in L* between firings of 1 mm Amber Mill specimens
30
35
40
45
50
55
60
65
70
B 1F 2F 3F 4F 5F
Amber Mill 1 mm
81
5.3.1 a* overall comparison
When the a* results are negative, the specimens have a green component, and if
the a* are positive, the specimens have a red component.
In the overall comparison the a* values ranged from -1.59 (EX 1 mm) to -4.75
(AM 1 mm). AM 1 mm showed the lowest a* values. The differences between materials
were significant (p=0.000). NC and LS where the only ones without a significant
difference. The two thicknesses showed a significant difference. There were no
significant differences between firings.
Material
EX
0.5 mm
EX
1 mm
NC
0.5 mm
NC
1 mm
LS
0.5 mm
LS
1 mm
AM
0.5 mm
AM
1 mm
a*
Mean -2.05 -1.59 -2.44 -2.17 -2.75 -2.02 -4.26 -4.75
SD 0.13 0.08 0.22 0.10 0.36 0.29 0.84 0.92
Min -2.15 -1.70 -3.25 -2.64 -5.30 -2.60 -6.31 -6.59
Max -1.15 -1.24 -1.80 -1.74 -2.01 -0.69 -2.97 -2.67
Table 50. Overall materials mean, standard deviation, minimum and maximum values of a*
Figure 66. Overall mean a* values of each material and thickness
-2.05
-2.44
-2.75
-4.26
-1.59
-2.17
-2.02
-4.75
-5
-5
-4
-4
-3
-3
-2
-2
-1
-1
0
IPS e.max CAD n!ce Initial LiSi Block Amber Mill
Thickness
a*
0.5 mm 1 mm
82
Figure 67. Overall changes in a* between firings of 0.5 mm specimens
Figure 68. Overall changes in a* between firings of 1 mm specimens
-6
-5
-4
-3
-2
-1
0
B 1F 2F 3F 4F 5F
a* 0.5 mm
IPS e.max CAD n!ce Initial LiSi Block Amber Mill
-6
-5
-4
-3
-2
-1
0
B 1F 2F 3F 4F 5F
a* 1 mm
IPS e.max CAD n!ce Initial LiSi Block Amber Mill
83
a. a* overall comparison between different materials
Material
IPS e.max
CAD
n!ce
Initial LiSi
Block
Amber
Mill
a*
Mean -1.82 -2.30 -2.39 -4.50
SD 0.25 0.22 0.49 0.91
Min -2.15 -3.25 -5.30 -6.59
Max -1.15 -1.74 -0.69 -2.67
Table 51. Overall material mean, standard deviation, minimum and maximum values
When the materials were compared to each other, regardless of their thicknesses
and the number of firings, AM showed the lowest a* values (mean = -4.50), followed
by LS (mean = -2.39), and NC (mean = -2.30). The material with the highest a* was EX
(mean = -1.82).
The Kruskal-Wallis test revealed that the difference between materials was
significant (p=0.000).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference between EX and NC (p=0.000), EX and LS (p=0.000), EX and AM
(p=0.000), AM and NC, (p=0.000) and AM and LS (p=0.000). There was not a significant
difference between NC and LS (p=1.000).
Pairwise Comparisons of Material
Adj. Sig.*
IPS e.max CAD-n!ce 0.000
IPS e.max CAD- Initial LiSi Block 0.000
IPS e.max CAD- Amber Mill 0.000
n!ce -Initial LiSi Block 1.000
Amber Mill-n!ce 0.000
Amber Mill-Initial LiSi Block 0.000
Table 52. Overall pairwise comparison between materials
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
84
Figure 69. Boxplot of a* for each material. *** (significant difference)
85
b. Overall comparison between different thicknesses
Thickness
0.5 mm 1 mm
a*
Mean -2.87 -2.63
SD 0.96 1.33
Min -6.31 -6.59
Max -1.15 -0.69
Table 53. Thicknesses mean, standard deviation, minimum and maximum values
When the thicknesses were compared to each other, regardless of the material and
the number of firings, the specimens with a thickness of 1 mm presented a lower a* (mean
= -2.63) than the specimens with a 0.5 mm thickness (mean = -2.87).
The Mann- Whitney U test revealed that this difference was significant (p=0.002).
Figure 70. Boxplot of a* for each thickness.
86
c. Overall comparison between different firings
Firings
Mean SD Min Max
a*
B -2.82 1.09 -5.91 -1.57
1F -2.71 1.08 -6.17 -1.34
2F -2.74 1.22 -6.59 -1.51
3F -2.79 1.29 -6.37 -0.69
4F -2.78 1.17 -5.79 -1.27
5F -2.68 1.17 -6.31 -1.15
Table 54. Firings mean, standard deviation, minimum and maximum values
When the firings were compared to each other, regardless of the material and the
thicknesses, the lowest a* was obtained by B (mean = -2.82) followed by 3F (mean = -
2.79), 4F (mean = -2.78), 2F (mean = -2.74), 1F (mean = -2.71) and the highest a* was
obtained by 5F (mean = -2.68).
The Kruskal-Wallis test revealed that the differences between firings was not
significant (p=0.611).
Figure 71. Boxplot of a* for each firing.
87
5.3.2 IPS e.max CAD Comparisons
a. IPS e.max CAD Thickness
Thickness IPS e.max CAD
0.5 mm 1 mm
a*
Mean -2.05 -1.59
SD 0.13 0.08
Min -2.15 -1.70
Max -1.15 -1.24
Table 55. IPS e.max CAD thicknesses’ mean, standard deviation, minimum and maximum values
The EX-specimens with a thickness of 1 mm showed a lower a* (mean = -1.59)
than the 0.5 mm thick specimens (mean = -2.05).
When EX thicknesses were compared to each other, the Mann- Whitney U test
revealed that the difference between thicknesses was significant (p<0.001).
Figure 72. Boxplot of a* for each IPS e.max CAD thickness.
88
b. IPS e.max CAD 0.5 mm Firings
Firings IPS e.max CAD 0.5 mm
Mean SD Min Max
a*
B -2.02 0.12 -2.11 -1.61
1F -2.09 0.04 -2.15 -2.02
2F -2.01 0.12 -2.12 -1.60
3F -2.06 0.04 -2.11 -1.95
4F -2.08 0.03 -2.14 -2.04
5F -2.04 0.25 -2.15 -1.15
Table 56. IPS e.max CAD 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the EX 0.5 mm firings were compared to each other,1F showed the lowest
a* (mean = -2.09) followed by 4F (mean = -2.08), 3F (mean = -2.06), 5F (mean = -2.04),
and B (mean = -2.02). 2F showed the highest a* (mean = -2.01).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the EX 0.5 mm specimens between B and 5F (p=0.034).
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
IPS e.max CAD 0.5 mm
B-1F 0.099
B-2F 1.000
B-3F 1.000
B-4F 0.272
B-5F 0.034
Table 57. Pairwise comparison between firings of EX 0.5 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
89
Figure 73. Changes in a* between firings of 0.5 mm IPS e.max CAD specimens
c. IPS e.max CAD 1 mm Firings
Firings IPS e.max CAD 1 mm
Mean SD Min Max
a*
B -1.62 0.03 -1.70 -1.57
1F -1.63 0.09 -1.69 -1.34
2F -1.57 0.04 -1.67 -1.51
3F -1.55 0.09 -1.63 -1.24
4F -1.60 0.10 -1.67 -1.27
5F -1.55 0.03 -1.59 -1.47
Table 58. IPS e.max CAD 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the EX 1 mm firings were compared to each other, 1F showed the lowest
a* (mean = -1.63) followed by B (mean = -1.62), 4F (mean = -1.60), 2F (mean = -1.57),
4F and 5F showed the highest a* (mean = -1.55).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the EX 1 mm specimens between B and 5F (p=0.034).
-3,0
-2,8
-2,6
-2,4
-2,2
-2,0
-1,8
-1,6
-1,4
-1,2
-1,0
B 1F 2F 3F 4F 5F
IPS e.max CAD 0.5 mm
90
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
IPS e.max CAD 1 mm
B-1F 1.000
B-2F 0.098
B-3F 0.104
B-4F 1.000
B-5F 0.001
Table 59. Pairwise comparison between firings of EX 1 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
Figure 74. Changes in a* between firings of 1 mm IPS e.max CAD specimens
-3,0
-2,8
-2,6
-2,4
-2,2
-2,0
-1,8
-1,6
-1,4
-1,2
-1,0
B 1F 2F 3F 4F 5F
IPS e.max CAD 1 mm
91
5.3.3 n!ce Comparisons
a. n!ce Thickness
Thickness n!ce
0.5 mm 1 mm
a*
Mean -2.44 -2.17
SD 0.22 0.10
Min -3.25 -2.64
Max -1.80 -1.74
Table 60. n!ce thicknesses’ mean, standard deviation, minimum and maximum values
When NC thicknesses were compared to each other, the a* of the 1 mm specimens
was higher (mean = -2.17) than the a* of the 0.5 mm specimens (mean = -2.44).
The Mann- Whitney U test revealed that the difference between thicknesses was
significant (p<0.001).
Figure 75. Boxplot of a* for n!ce thicknesses. *** (significant difference)
92
b. n!ce 0.5 mm Firings
Firings n!ce 0.5 mm
Mean SD Min Max
a*
B -2.63 0.28 -3.25 -1.98
1F -2.42 0.16 -2.64 -2.03
2F -2.39 0.15 -2.63 -2.05
3F -2.41 0.18 -2.76 -2.09
4F -2.37 0.25 -2.67 -1.80
5F -2.39 0.15 -2.66 -1.99
Table 61. n!ce 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the NC 0.5 mm firings were compared to each other, B showed the lowest
a* (mean = -2.63) followed by 1F (p= -2.42), 3F (mean = -2.41), 2F and 5F (mean = -
2.39). 4F showed the highest a* (mean = -2.37).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p=0.009).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the NC 0.5 mm specimens between B and 2F (p=0.021), B and
3F (P=0.026), and B and 5F (p=0.026).
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
n!ce 0.5 mm
B-1F 0.119
B-2F 0.021
B-3F 0.026
B-4F 0.072
B-5F 0.026
Table 62. Pairwise comparison between firings of NC 0.5 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
93
Figure 76. Changes in a* between firings of 0.5 mm n!ce specimens
c. n!ce 1 mm Firings
Firings n!ce 1 mm
Mean SD Min Max
a*
B -2.27 0.18 -2.64 -1.74
1F -2.20 0.06 -2.28 -2.05
2F -2.16 0.05 -2.22 -2.07
3F -2.14 0.06 -2.25 -2.04
4F -2.12 0.08 -2.26 -1.97
5F -2.13 0.05 -2.26 -2.04
Table 63. n!ce 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the NC 1 mm firings were compared to each other, B showed the lowest a*
(mean = -2.27) followed by 1F (mean = -2.20), 2F (mean = -2.16), 3F (mean = -2.14), 5F
(mean = -2.13). 4F showed the highest a* (mean = -2.12).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the NC 1mm specimens between B and 2F (p=0.015), B and 3F
(p= 0.000), B and 4F p= 0.000) and B-5F (p=0.000).
-3,0
-2,5
-2,0
-1,5
-1,0
-0,5
0,0
B 1F 2F 3F 4F 5F
n!ce 0.5 mm
94
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
n!ce 1 mm
B-1F 1.000
B-2F 0.015
B-3F 0.000
B-4F 0.000
B-5F 0.000
Table 64. Pairwise comparison between firings of NC 1 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
Figure 77. Changes in a* between firings of 1 mm n!ce specimens
-3,0
-2,5
-2,0
-1,5
-1,0
-0,5
0,0
B 1F 2F 3F 4F 5F
n!ce 1 mm
95
5.3.4 Initial LiSi Block Comparisons
a. Initial LiSi Block Thickness
Thickness Initial LiSi Block
0.5 mm 1 mm
a*
Mean -2.75 -2.02
SD 0.36 0.29
Min -5.30 -2.60
Max -2.01 -0.69
Table 65. Initial LiSi Block thicknesses’ mean, standard deviation, minimum and maximum values
When LS thicknesses were compared to each other, the a* of the 0.5 mm thick
specimens was lower (mean = -2.75) than the 1 mm thick specimens (mean = -2.02).
The Mann- Whitney U test revealed that the difference between thicknesses was
significant (p<0.001).
Figure 78. Boxplot of a* for Initial LiSi Block thicknesses. *** (significant difference)
96
b. Initial LiSi Block 0.5 mm Firings
Firings Initial LiSi Block 0.5 mm
Mean SD Min Max
a*
B -2.93 0.25 -3.47 -2.58
1F -2.67 0.29 -3.20 -2.01
2F -2.72 0.24 -3.23 -2.40
3F -2.71 0.16 -3.08 -2.54
4F -2.68 0.21 -3.13 -2.34
5F -2.78 0.72 -5.30 -2.29
Table 66. Initial LiSi Block 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the LS 0.5 mm firings were compared to each other, B showed the lowest
a* (mean = -2.93) followed by 5F (mean = -2.78), 2F (mean = -2.72), 3F (mean = -2.71),
and 4F (mean = -2.68). 1F showed the highest a* (mean = -2.67).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p=0.007).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the LS 0.5 mm specimens between B and 5F (p=0.003).
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
Initial LiSi Block 0.5 mm
B-1F 0.084
B-2F 0.133
B-3F 0.308
B-4F 0.074
B-5F 0.003
Table 67. Pairwise comparison between firings of LS 0.5 mm specimens
97
Figure 79. Changes in a* between firings of 0.5 mm Initial LiSi Block specimens
c. Initial LiSi Block 1 mm Firings
Firings Initial LiSi Block 1 mm
Mean SD Min Max
a*
B -2.26 0.29 -2.60 -1.62
1F -1.96 0.21 -2.26 -1.50
2F -2.00 0.18 -2.28 -1.63
3F -1.82 0.46 -2.29 -0.69
4F -2.07 0.14 -2.31 -1.76
5F -2.04 0.21 -2.36 -1.54
Table 68. Initial LiSi Block 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the LS 1 mm firings were compared to each other, B showed the lowest a*
(mean = -2.26) followed by 4F (mean = -2.07), 5F (mean = -2.04), 2F (mean = -2.00),
and 1F (mean = -1.96) and 3F showed the highest a* (mean = -1.82).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p=0.002).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the LS 1 mm specimens between B and 1F (p=0.007), B and 2F
(p=0.024), and B and 3F (p=0.003).
-3,5
-3,0
-2,5
-2,0
-1,5
-1,0
B 1F 2F 3F 4F 5F
Initial LiSi Block 0.5 mm
98
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
Initial LiSi Block 1 mm
B-1F 0.007
B-2F 0.024
B-3F 0.003
B-4F 0.319
B-5F 0.283
Table 69. Pairwise comparison between firings of LS 1 mm specimens
Figure 80. Changes in a* between firings of 1 mm Initial LiSi Block specimens
-3,0
-2,8
-2,6
-2,4
-2,2
-2,0
-1,8
-1,6
-1,4
-1,2
-1,0
B 1F 2F 3F 4F 5F
Initial LiSi Block 1 mm
99
5.3.5 Amber Mill Comparisons
a. Amber Mill Thickness
Thickness Amber Mill
0.5 mm 1 mm
a*
Mean -4.26 -4.75
SD 0.84 0.92
Min -6.31 -6.59
Max -2.97 -2.67
Table 70. Amber Mill thicknesses’ mean, standard deviation, minimum and maximum values
The a* of the 1 mm thick specimens was lower (mean = -4.75) than the 0.5 mm
thick specimens (mean = -4.26).
When AM thicknesses were compared to each other, the Mann- Whitney U test
revealed that the difference between thicknesses was significant (p<0.010).
Figure 81. Boxplot of a* for Amber Mill thicknesses *** (significant difference)
100
b. Amber Mill 0.5 mm Firings
Firings Amber Mill 0.5 mm
Mean SD Min Max
a*
B -3.83 0.52 -4.75 -2.99
1F -3.67 0.44 -4.50 -3.29
2F -3.64 0.35 -4.38 -3.31
3F -4.27 0.57 -5.29 -3.65
4F -4.96 0.60 -5.79 -4.17
5F -5.20 0.88 -6.31 -2.97
Table 71. Amber Mill 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the AM 0.5 mm firings were compared to each other, 5F showed the lowest
a* (mean = -5.20) followed by 4F (mean -4.96), 3F (mean = -4.27), B (mean = -3.83),
and 1F (mean = -3.67). 2F showed the highest a* (mean = -3.64).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the AM 0.5 mm specimens between B and 4F (p=0.011) and B
and 5F (p=0.002).
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
Amber Mill 0.5 mm
B-1F 1.000
B-2F 1.000
B-3F 1.000
B-4F 0.011
B-5F 0.002
Table 72. Pairwise comparison between firings of AM 0.5 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
101
Figure 82. Changes in a* between firings of 0.5 mm Amber Mill specimens
c. Amber Mill 1 mm Firings
Firings Amber Mill 1 mm
Mean SD Min Max
a*
B -5.03 0.47 -5.91 -3.81
1F -5.02 0.56 -6.17 -3.96
2F -5.46 0.71 -6.59 -3.52
3F -5.34 0.58 -6.37 -4.08
4F -4.34 0.51 -5.27 -3.60
5F -3.30 0.51 -4.20 -2.67
Table 73. Amber Mill 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the AM 1 mm firings were compared to each other, 2F showed the lowest
a* (mean = -5.46) followed by 3F (mean = -5.34), B (mean = -5.03), 1F (mean = -5.02),
and 4F (mean = -4.34). 5F showed the highest a* (mean = -3.30).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the AM 1 mm specimens between B and 5F (p=0.000).
-6,0
-5,0
-4,0
-3,0
-2,0
-1,0
0,0
B 1F 2F 3F 4F 5F
Amber Mill 0.5 mm
102
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
Amber Mill 1 mm
B-1F 1.000
B-2F 0.916
B-3F 1.000
B-4F 0.344
B-5F 0.000
Table 74. Pairwise comparison between firings of AM 1 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
Figure 83. Changes in a* between firings of 1 mm Amber Mill specimens
-6,0
-5,0
-4,0
-3,0
-2,0
-1,0
0,0
B 1F 2F 3F 4F 5F
Amber Mill 1 mm
103
5.4.1 b* overall comparison
When the b* results are negative, the specimens have a blue component, and if
the a* are positive, the specimens have a yellow component.
In the overall comparison the b* values ranged from -5.23 (AM 0.5 mm) to 5.39
(NC 1 mm). AM 0.5 mm showed the lowest b* values. The differences between
materials were significant (p<0.001). The two thicknesses showed a significant
difference. There was a significant difference between firings (p<0.001).
Material
EX
0.5 mm
EX
1 mm
NC
0.5 mm
NC
1 mm
LS
0.5 mm
LS
1 mm
AM
0.5 mm
AM
1 mm
b*
Mean -0.18 5.16 0.54 5.39 -2.50 3.70 -5.23 4.11
SD 0.22 0.21 0.48 0.22 0.86 0.58 2.25 4.52
Min -0.64 4.36 -0.75 4.77 -5.59 2.45 -10.70 -4.29
Max 0.26 5.59 1.49 5.87 -0.50 5.26 0.25 11.80
Table 75. Overall materials mean, standard deviation, minimum and maximum values of b*
Figure 84. Overall mean b* values of each material and thickness
-0.18
0.54
-2.50
-5.23
5.16
5.39
3.70
4.11
-6,00
-4,00
-2,00
0,00
2,00
4,00
6,00
IPS e.max CAD n!ce Initial LiSi Block Amber Mill
Thickness
b*
0.5 mm 1 mm
104
Figure 85. Overall changes in b* between firings of 0.5 mm specimens
Figure 86. Overall changes in b* between firings of 1 mm specimens
-7,00
-6,00
-5,00
-4,00
-3,00
-2,00
-1,00
0,00
1,00
2,00
B 1F 2F 3F 4F 5F
b* 0.5 mm
IPS e.max CAD n!ce Initial LiSi Block Amber Mill
-2,00
0,00
2,00
4,00
6,00
8,00
10,00
12,00
B 1F 2F 3F 4F 5F
b* 1 mm
IPS e.max CAD n!ce Initial LiSi Block Amber Mill
105
a. b* overall comparison between different materials
Material
IPS e.max
CAD
n!ce
Initial LiSi
Block
Amber
Mill
b*
Mean 2.49 2.97 0.60 -0.56
SD 2.69 2.46 3.19 5.88
Min -0.64 -0.75 -5.59 -10.70
Max 5.59 5.87 5.26 11.80
Table 76. Overall material mean, standard deviation, minimum and maximum values
When the materials were compared to each other, regardless of their thicknesses
and the number of firings, AM showed the lowest b* values (mean = -0.56), followed
by LS (mean = 0.60), and EX (mean = 2.49). The material with the highest b* was NC
(mean = 2.97).
The Kruskal-Wallis test revealed that the difference between materials was
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference between NC and LS (p=0.001), and AM and NC (p=0.000).
Pairwise Comparisons of Material
Adj. Sig.*
IPS e.max CAD-n!ce 0.736
IPS e.max CAD- Initial LiSi Block 0.154
IPS e.max CAD- Amber Mill 1.000
n!ce -Initial LiSi Block 0.001
Amber Mill-n!ce 0.000
Amber Mill-Initial LiSi Block 1.000
Table 77. Overall pairwise comparison between materials
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
106
Figure 87. Boxplot of b* for each material. *** (significant difference)
107
b. Overall comparison between different thicknesses
Thickness
0.5 mm 1 mm
b*
Mean -1.84 4.59
SD 2.57 2.38
Min -10.70 -4.29
Max 1.49 11.80
Table 78. Thicknesses mean, standard deviation, minimum and maximum values
When the thicknesses were compared to each other, regardless of the material and
the number of firings, the specimens with a thickness of 0.5 mm presented a lower b*
(mean = -1.84) than the specimens with a 1mm thickness (mean = 4.59).
The Mann- Whitney U test revealed that this difference was significant (p=0.000).
Figure 88. Boxplot of b* for each thickness.
108
c. Overall comparison between different firings
Firings
Mean SD Min Max
b*
B 1.10 3.46 -7.95 5.43
1F 0.60 3.70 -9.24 5.41
2F 0.81 3.82 -10.70 5.59
3F 1.33 4.16 -10.30 7.04
4F 1.97 4.42 -8.69 10.51
5F 2.44 4.47 -6.03 11.80
Table 79. Firings mean, standard deviation, minimum and maximum values
When the firings were compared to each other, regardless of the material and the
thicknesses, the lowest b* was obtained by 1F (mean = 0.60) followed by 2F (mean =
0.81), B (mean = 1.10), 3F (mean = 1.33), 4F (mean = 1.97) and the highest b* was
obtained by 5F (mean = 2.44).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p>0.05).
Figure 89. Boxplot of b* for each firing.
109
5.4.2 IPS e.max CAD Comparisons
a. IPS e.max CAD Thickness
Thickness IPS e.max CAD
0.5 mm 1 mm
b*
Mean -0.18 5.16
SD 0.22 0.21
Min -0.64 4.36
Max 0.26 5.59
Table 80. IPS e.max CAD thicknesses’ mean, standard deviation, minimum and maximum values
The EX-specimens with a thickness of 0.5 mm showed a lower b* (mean = -0.18)
than the 1 mm thick specimens (mean = 5.16).
When EX thicknesses were compared to each other, the Mann- Whitney U test
revealed that the difference between thicknesses was significant (p<0.001).
Figure 90. Boxplot of b* for each IPS e.max CAD thickness.
110
b. IPS e.max CAD 0.5 mm Firings
Firings IPS e.max CAD 0.5 mm
Mean SD Min Max
b*
B -0.33 0.20 -0.64 0.01
1F -0.28 0.21 -0.57 0.10
2F -0.22 0.21 -0.56 0.18
3F -0.05 0.22 -0.38 0.26
4F -0.14 0.17 -0.44 0.11
5F -0.08 0.22 -0.46 0.26
Table 81. IPS e.max CAD 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the EX 0.5 mm firings were compared to each other, B showed the lowest
b* (mean = -0.33) followed by 1F (mean = -0.28), 2F (mean = -0.22), 4F (mean = -0.14)
and 5F (mean = -0.08). 3F showed the highest a* (mean = -0.05).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p=0.003).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the EX 0.5 mm specimens between B and 3F (p=0.016) and B
and 5F (p=0.033).
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
IPS e.max CAD 0.5 mm
B-1F 1.000
B-2F 1.000
B-3F 0.016
B-4F 0.291
B-5F 0.033
Table 82. Pairwise comparison between firings of EX 0.5 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
111
Figure 91. Changes in b* between firings of 0.5 mm IPS e.max CAD specimens
c. IPS e.max CAD 1 mm Firings
Firings IPS e.max CAD 1 mm
Mean SD Min Max
b*
B 4.91 0.21 4.36 5.21
1F 5.05 0.09 4.91 5.22
2F 5.12 0.13 4.92 5.41
3F 5.23 0.13 4.96 5.45
4F 5.29 0.12 5.08 5.51
5F 5.38 0.12 5.19 5.59
Table 83. IPS e.max CAD 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the EX 1 mm firings were compared to each other, B showed the lowest b*
(mean = 4.91) followed by 1F (mean = 5.05), 2F (mean = 5.12), 3F (mean = 5.23), 4F
(mean = 5.29), and 5F showed the highest b* (mean = 5.38).
The Kruskal-Wallis test revealed that the differences between firings were NOT
significant (p<0,001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the EX 1 mm specimens between B and 3F (p=0.001), B and 4F
(p=0.000), and B and 5F (p=0.000).
-1
0
1
2
3
4
5
6
B 1F 2F 3F 4F 5F
IPS e.max CAD 0.5 mm
112
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
IPS e.max CAD 1 mm
B-1F 1.000
B-2F 0.458
B-3F 0.001
B-4F 0.000
B-5F 0.000
Table 84. Pairwise comparison between firings of EX 1 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
Figure 92. Changes in b* between firings of 1 mm IPS e.max CAD specimens
-1
0
1
2
3
4
5
6
B 1F 2F 3F 4F 5F
IPS e.max CAD 1 mm
113
5.4.3 n!ce Comparisons
a. n!ce Thickness
Thickness n!ce
0.5 mm 1 mm
b*
Mean 0.54 5.39
SD 0.48 0.22
Min -0.75 4.77
Max 1.49 5.87
Table 85. n!ce thicknesses’ mean, standard deviation, minimum and maximum values
When NC thicknesses were compared to each other, the b* of the 1 mm specimens
was higher (mean = 5.39) than the b* of the 0.5 mm specimens (mean = 0.54).
The Mann- Whitney U test revealed that the difference between thicknesses was
significant (p<0.001).
Figure 93. Boxplot of b* for n!ce thicknesses. *** (significant difference)
114
b. n!ce 0.5 mm Firings
Firings n!ce 0.5 mm
Mean SD Min Max
b*
B 0.10 0.48 -0.75 0.81
1F 0.42 0.44 -0.69 0.94
2F 0.58 0.45 -0.24 1.10
3F 0.60 0.40 -0.49 1.15
4F 0.69 0.41 -0.31 1.12
5F 0.85 0.36 0.27 1.49
Table 86. n!ce 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the NC 0.5 mm firings were compared to each other, B showed the lowest
b* (mean = 0.10) followed by 1F (p= 0.42), 2F (mean = 0.58), 3F (mean = 0.60), and 4F
(mean = 0.69). 5F showed the highest b* (mean = 0.85).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the NC 0.5 mm specimens between B and 4F (p=0.010) and B
and 5F (p=0.000).
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
n!ce 0.5 mm
B-1F 1.000
B-2F 0.121
B-3F 0.106
B-4F 0.010
B-5F 0.000
Table 87. Pairwise comparison between firings of NC 0.5 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
115
Figure 94. Changes in b* between firings of 0.5 mm n!ce specimens
c. n!ce 1 mm Firings
Firings n!ce 1 mm
Mean SD Min Max
b*
B 5.14 0.18 4.81 5.43
1F 5.22 0.17 4.77 5.41
2F 5.48 0.14 5.00 5.59
3F 5.46 0.16 5.05 5.74
4F 5.47 0.14 5.09 5.64
5F 5.56 0.13 5.24 5.87
Table 88. n!ce 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the NC 1 mm firings were compared to each other, B showed the lowest b*
(mean = 5.14) followed by 1F (mean = 5.22), 3F (mean = 5.46), 4F (mean = 5.47), 2F
(mean = 5.48). 5F showed the highest b* (mean = 5.56).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the NC 1mm specimens between B and 2F (p=0.000), B and 3F
(p=0.005), B and 4F (p= 0.001), and B-5F (p=0.000).
0,00
1,00
2,00
3,00
4,00
5,00
6,00
B 1F 2F 3F 4F 5F
n!ce 0.5 mm
116
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
n!ce 1 mm
B-1F 1.000
B-2F 0.000
B-3F 0.005
B-4F 0.001
B-5F 0.000
Table 89. Pairwise comparison between firings of NC 1 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
Figure 95. Changes in b* between firings of 1 mm n!ce specimens
0,00
1,00
2,00
3,00
4,00
5,00
6,00
B 1F 2F 3F 4F 5F
n!ce 1 mm
117
5.4.4 Initial LiSi Block Comparisons
a. Initial LiSi Block Thickness
Thickness Initial LiSi Block
0.5 mm 1 mm
b*
Mean -2.50 3.70
SD 0.86 0.58
Min -5.59 2.45
Max -0.50 5.26
Table 90. Initial LiSi Block thicknesses’ mean, standard deviation, minimum and maximum values
When LS thicknesses were compared to each other, the b* of the 0.5 mm thick
specimens was lower (mean = -2.50) than the 1 mm thick specimens (mean = 3.70).
The Mann- Whitney U test revealed that the difference between thicknesses was
significant (p<0.001).
Figure 96. Boxplot of b* for Initial LiSi Block thicknesses. *** (significant difference)
118
b. Initial LiSi Block 0.5 mm Firings
Firings Initial LiSi Block 0.5 mm
Mean SD Min Max
b*
B -1.77 0.81 -3.19 -0.50
1F -2.50 0.75 -3.95 -1.11
2F -2.61 0.75 -3.91 -1.17
3F -2.74 1.08 -5.59 -0.98
4F -2.62 0.75 -3.99 -1.20
5F -2.74 0.73 -4.07 -1.33
Table 91. Initial LiSi Block 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the LS 0.5 mm firings were compared to each other, 3F and 5F showed the
lowest b* (mean = -2.74) followed by 4F (mean = -2.62), 2F (mean = 2.61), and 1F (mean
= -2.50). B showed the highest b* (mean = -1.77).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p=0.021).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the LS 0.5 mm specimens between B and 5F (p=0.020).
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
Initial LiSi Block 0.5 mm
B-1F 0.442
B-2F 0.140
B-3F 0.087
B-4F 0.095
B-5F 0.020
Table 92. Pairwise comparison between firings of LS 0.5 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
119
Figure 97. Changes in b* between firings of 0.5 mm Initial LiSi Block specimens
c. Initial LiSi Block 1 mm Firings
Firings Initial LiSi Block 1 mm
Mean SD Min Max
b*
B 4.63 0.41 3.71 5.26
1F 3.61 0.37 2.80 4.25
2F 3.56 0.38 2.80 4.10
3F 3.61 0.38 2.63 4.01
4F 3.33 0.41 2.45 3.81
5F 3.44 0.42 2.55 4.06
Table 93. Initial LiSi Block 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the LS 1 mm firings were compared to each other, 4F showed the lowest
b* (mean = 3.33) followed by 5F (mean = 3.44), 2F (mean = 3.56), 1F and 3F (mean =
3.61) and B showed the highest a* (mean = 4.63).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the LS 1 mm specimens between B and 1F (p=0.001), B and 2F
(p=0.000), B and 3F (p=0.002), B and 4F (p=0.000), and B and 5F (p=0.000).
-4
-3
-2
-1
0
1
2
3
4
5
B 1F 2F 3F 4F 5F
Initial LiSi Block 0.5 mm
120
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
Initial LiSi Block 1 mm
B-1F 0.001
B-2F 0.000
B-3F 0.002
B-4F 0.000
B-5F 0.000
Table 94. Pairwise comparison between firings of LS 1 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
Figure 98. Changes in b* between firings of 1 mm Initial LiSi Block specimens
-3
-2
-1
0
1
2
3
4
5
B 1F 2F 3F 4F 5F
Initial LiSi Block 1 mm
121
5.4.5 Amber Mill Comparisons
a. Amber Mill Thickness
Thickness Amber Mill
0.5 mm 1 mm
b*
Mean -5,23 4,11
SD 2,25 4,52
Min -10,70 -4,29
Max 0,25 11,80
Table 95. Amber Mill thicknesses’ mean, standard deviation, minimum and maximum values
The b* of the 0.5 mm thick specimens was lower (mean = -5.23) than the 1 mm
thick specimens (mean = 4.11).
When AM thicknesses were compared to each other, the Mann- Whitney U test
revealed that the difference between thicknesses was significant (p<0.001).
Figure 99. Boxplot of b* for Amber Mill thicknesses *** (significant difference)
122
b. Amber Mill 0.5 mm Firings
Firings Amber Mill 0.5 mm
Mean SD Min Max
b*
B -4.91 1.63 -7.95 -3.40
1F -5.55 2.19 -9.24 -3.04
2F -6.11 2.07 -10.70 -3.89
3F -6.43 2.21 -10.30 -4.63
4F -5.02 2.22 -8.69 -1.94
5F -3.36 2.04 -6.03 0.25
Table 96. Amber Mill 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the AM 0.5 mm firings were compared to each other, 3F showed the lowest
b* (mean = -6.43) followed by 2F (mean -6.11), 1F (mean = -5.55), 4F (mean = -5.02),
and B (mean = -4.91). 5F showed the highest b* (mean = -3.36).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p>0.001).
Figure 100. Changes in b* between firings of 0.5 mm Amber Mill specimens
-8
-6
-4
-2
0
2
4
6
8
10
12
B 1F 2F 3F 4F 5F
Amber Mill 0.5 mm
123
c. Amber Mill 1 mm Firings
Firings Amber Mill 1 mm
Mean SD Min Max
a*
B 1.03 1.00 -1.51 2.13
1F -1.15 1.27 -4.29 0.24
2F 0.69 1.55 -2.37 2.85
3F 4.93 1.49 2.54 7.04
4F 8.76 1.47 6.55 10.51
5F 10.43 1.17 8.46 11.80
Table 97. Amber Mill 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the AM 1 mm firings were compared to each other, 1F showed the lowest
b* (mean = -1.15) followed by 2F (mean = 0.69), B (mean = 1.03), 3F (mean = 4.93), and
4F (mean = 8.76). 5F showed the highest b* (mean = 10.43).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference in the AM 1 mm specimens between B and 4F (p=0.000) and B and
5F (p=0.000).
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
Amber Mill 1 mm
B-1F 0.685
B-2F 1.000
B-3F 0.243
B-4F 0.000
B-5F 0.000
Table 98. Pairwise comparison between firings of AM 1 mm specimens
*Significance values have been adjusted by the Bonferroni correction for multiple tests
124
Figure 101. Changes in b* between firings of 1 mm Amber Mill specimens
-7
-5
-3
-1
1
3
5
7
9
11
B 1F 2F 3F 4F 5F
Amber Mill 1 mm
125
5.5 Translucency Parameter Analysis
5.5.1 Overall Comparisons
In the Overall comparisons the AM 0.5 mm specimens showed the highest
translucency and the NC 1 mm specimens showed the lowest translucency. The
differences between materials were significant (EX and AM, NC and LS, NC and AM,
LS and AM). The two thicknesses presented a significant difference. There was a
significant difference between firings (TPB and TP5).
Material
EX
0.5 mm
EX
1 mm
NC
0.5 mm
NC
1 mm
LS
0.5 mm
LS
1 mm
AM
0.5 mm
AM
1 mm
TP
Mean 27.43 19.61 23.56 17.58 27.08 20.77 38.11 27.42
SD 0.54 0.27 0.88 0.43 1.89 1.04 3.7 5.72
Min 25.68 18.83 22.04 16.4 22.48 17.57 28.59 17.17
Max 28.56 20.58 25.7 18.6 31.00 22.85 46.85 38.56
Table 99. Overall materials mean, standard deviation, minimum and maximum values divided by thicknesses
Figure 102. Overall mean TP of each material and thickness
27.43
23.56
27.08
38.11
19.61
17.58
20.77
27.42
0
5
10
15
20
25
30
35
40
45
IPS e.max CAD n!ce Initial LiSi Block Amber Mill
Thickness
TP
0.5 mm 1 mm
126
Figure 103. Lithium Disilicate materials' translucency after multiple firings
Figure 104. Overall changes in TP between firings of 0.5 mm specimens
0
5
10
15
20
25
30
35
40
45
B 1F 2F 3F 4F 5F
TP 0.5 mm
IPS e.max CAD n!ce Initial LiSi Block Amber Mill
127
Figure 105. Overall changes in TP between firings of 1 mm specimens
0
5
10
15
20
25
30
35
40
B 1F 2F 3F 4F 5F
TP 1 mm
IPS e.max CAD n!ce Initial LiSi Block Amber Mill
128
a. Overall comparison between different materials
Material
IPS e.max
CAD n!ce
Initial LiSi
Block
Amber
Mill
TP
Mean 23.52 20.57 23.92 32.76
SD 3.94 3.08 3.51 7.2
Min 18.83 16.4 17.57 17.17
Max 18.56 25.70 31.00 46.85
Table 100. Material mean, standard deviation, minimum and maximum values
When the materials were compared to each other, regardless of their thicknesses
and the number of firings, NC showed the lowest TP values (mean = 20.57), followed by
EX (mean = 23.52), and LS (23.92). The material with the highest TP was AM (mean =
32,76).
The Kruskal-Wallis test revealed that the difference between materials was
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference between NC and LS (p=0.014), NC and AM (p=0.000), EX and
AM (p=0.000), and LS and AM, (p=0.000) There was no significant difference between
NC and EX (p=0.055) and EX and LS (p=1.000).
Pairwise Comparisons of Material
Sig. Adj. Sig.
*
IPS e.max CAD - Initial LiSi Block 0.664 1.000
IPS e.max CAD - Amber Mill <0.001 0.000
n!ce - IPS e.max CAD 0.009 0.055
n!ce - Initial LiSi Block 0.002 0.014
n!ce - Amber Mill <0.001 0.000
Initial LiSi Block - Amber Mill <0.001 0.000
Table 101. Pairwise comparison between materials
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
129
Figure 106. Boxplot of TP for each material. *** (significant difference)
130
b. Overall comparison between different thicknesses
Thickness
0.5 mm 1 mm
TP
Mean 29.04 21.35
SD 5.86 4.7
Min 22.04 16.4
Max 46.85 38.56
Table 102. Thicknesses mean, standard deviation, minimum and maximum values
When the thicknesses were compared to each other, regardless of the material and
the number of firings, the 0.5 mm thick specimens presented a higher TP (mean = 29.04)
than the 1 mm thick specimens (mean = 21.35).
The Mann- Whitney U test revealed that the difference was significant (p<0.001).
Figure 107. Boxplot of TP for each thickness. *** (significant difference)
131
c. Overall comparison between different firings
Firings
Mean SD Min Max
TP
B 25.75 6.15 17.40 28.11
1F 26.38 7.45 16.45 28.56
2F 25.97 7.28 16.64 28.34
3F 25.19 6.58 16.64 27.95
4F 24.39 5.98 16.58 28.38
5F 23.5 5.34 16.40 28.48
Table 103. Firings mean, standard deviation, minimum and maximum values
When the firings were compared to each other, regardless of the material and the
thicknesses, the lowest TP was obtained by the 5F (mean = 23.5) followed by 4F (mean
= 24.39), 3F (mean = 25.19), B (mean = 25,75), and 2F (mean = 25.97) and the highest
ΔE was obtained by 1F (mean = 26.38).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p=0.19).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference between B and 5F (p=0.046).
Pairwise Comparisons of Firings
Adj. Sig.
*
B-1F 1.000
B-2F 1.000
B-3F 1.000
B-4F 0.978
B-5F 0.046
Table 104. Pairwise comparison between firings
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
132
Figure 108. Boxplot of TP for each firing. *** (significant difference)
133
5.2.2 IPS e.max CAD Comparisons
a. IPS e.max CAD Thickness
Thickness IPS e.max CAD
0.5 mm 1 mm
TP
Mean 27.43 19.61
SD 0.54 0.27
Min 25.68 18.83
Max 28.56 20.58
Table 105. IPS e.max CAD thicknesses’ mean, standard deviation, minimum and maximum values
When EX thicknesses were compared to each other, the EX-specimens with a
thickness of 1 mm showed a lower TP (mean = 19.61) than the 0.5 mm thick specimens
(mean = 27.43).
The Mann- Whitney U test revealed that the difference between thicknesses was
significant (p<0.001).
Figure 109. Boxplot of TP for each IPS e.max CAD thickness. *** (significant difference)
134
Figure 110. IPS e.max CAD specimens’ translucency after multiple firings
b. IPS e.max CAD 0.5 mm Firings
Firings IPS e.max CAD 0.5mm
Mean SD Min Max
TP
B 27.43 0.51 26.59 28.11
1F 27.36 0.58 26.42 28.56
2F 27.40 0.55 26.57 28.34
3F 27.25 0.43 26.61 27.95
4F 27.57 0.46 26.60 28.38
5F 27.55 0.70 25.58 28.48
Table 106. IPS e.max CAD 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the EX 0.5 mm firings were compared to each other, 3F presented the
lowest TP (mean = 27.25), followed by 1F (mean = 27.36), 2F (mean = 27.4), B (mean =
27.43), and 5F (mean = 27.55). 4F presented the highest TP (mean = 27.57).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p=0.404).
135
Figure 111. Changes in TP between firings of 0.5 mm IPS e.max CAD specimens
Figure 112. IPS e.max CAD 0.5 mm specimens’ translucency after multiple firings
c. IPS e.max CAD 1 mm Firings
Firings IPS e.max CAD 1 mm
Mean SD Min Max
TP
B 19.52 0.39 18.83 20.10
1F 19.69 0.26 19.05 19.98
2F 19.63 0.27 19.21 20.00
3F 19.58 0.32 19.14 20.58
4F 19.66 0.14 19.40 19.88
5F 19.58 0.21 19.18 19.94
Table 107. IPS e.max CAD 1 mm thickness’s mean, standard deviation, minimum and maximum values
19
20
21
22
23
24
25
26
27
28
B 1F 2F 3F 4F 5F
IPS e.max CAD 0.5 mm
136
When the EX 1 mm firings were compared to each other, B presented the lowest
TP (mean = 19.52), followed by 3F and 5F (mean = 19.58), 2F (mean = 19.63), and 4F
(mean = 19.66). 1F presented the highest TP (mean = 19.69).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p=0.446).
Figure 113. Changes in TP between firings of 1 mm IPS e.max CAD specimens
Figure 114. IPS e.max CAD 1 mm specimens’ translucency after multiple firing
19
20
21
22
23
24
25
26
27
28
B 1F 2F 3F 4F 5F
IPS e.max CAD 1 mm
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5.5.3 n!ce Comparisons
a. n!ce Thickness
Thickness n!ce
0.5 mm 1 mm
TP
Mean 23.56 17.58
SD 0.88 0.43
Min 22.04 16.4
Max 25.7 18.6
Table 108. n!ce thicknesses’ mean, standard deviation, minimum and maximum values
When NC thicknesses were compared to each other, the NC-specimens with a
thickness of 1 mm showed a lower TP (mean = 17.58) than the 0.5 mm thick specimens
(mean = 23.56).
The Mann- Whitney U test revealed that the difference between thicknesses was
significant (p<0.001).
Figure 115. Boxplot of TP for each n!ce thickness. *** (significant difference)
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Figure 116. n!ce specimens’ translucency after multiple firings
b. n!ce 0.5 mm Firings
Firings n!ce 0.5 mm
Mean SD Min Max
TP
B 24.29 0.66 23.41 25.39
1F 23.65 1.00 22.04 25.7
2F 23.45 0.83 22.43 25.33
3F 23.42 0.87 22.38 25.57
4F 23.36 0.77 22.46 25.13
5F 23.22 0.79 22.18 24.77
Table 109. n!ce 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the NC 0.5 mm firings were compared to each other, 5F presented the
lowest TP (mean = 23.22), followed by 4F (mean = 23.36), 3F (mean = 23.42), 2F (mean
= 23.45), and 1F (mean = 23.65). B presented the highest TP (mean = 24.29).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p=0.008).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference between B and 4F (p=0.008), and B and 5F (p=0.033).
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Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
n!ce 0.5 mm
B-1F 0.479
B-2F 0.079
B-3F 0.057
B-4F 0.033
B-5F 0.008
Table 110. Pairwise comparison between firings
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
Figure 117. Changes in TP between firings of 0.5 mm n!ce specimens
Figure 118. n!ce 0.5 mm specimens’ translucency after multiple firings
17
18
19
20
21
22
23
24
25
B 1F 2F 3F 4F 5F
n!ce 0.5 mm
140
c. n!ce 1 mm Firings
Firings n!ce 1 mm
Mean SD Min Max
TP
B 17.99 0.35 17.40 18.60
1F 17.63 0.42 16.45 18.30
2F 17.55 0.33 16.64 18.07
3F 17.60 0.46 16.64 18.46
4F 17.45 0.30 16.58 18.01
5F 17.26 0.41 16.40 17.96
Table 111. n!ce 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the NC 1 mm firings were compared to each other, 5F presented the lowest
TP (mean = 17.26), followed by 4F (mean = 17.45), 2F (mean = 17.55), 3F (mean =
17.60), and 1F (mean = 17.63). B presented the highest TP (mean = 17.99).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference between B and 4F (p=0.004), and B and 5F (p=0.000).
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
n!ce 1 mm
B-1F 0.833
B-2F 0.140
B-3F 0.083
B-4F 0.004
B-5F 0.000
Table 112. Pairwise comparison between firings
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
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Figure 119. Changes in TP between firings of 1 mm n!ce specimens
Figure 120. n!ce 1 mm specimens’ translucency after multiple firings
17
18
19
20
21
22
23
24
25
B 1F 2F 3F 4F 5F
n!ce 1 mm
142
5.5.4 Initial LiSi Block Comparisons
a. Initial LiSi Block Thickness
Thickness Initial LiSi Block
0.5 mm 1 mm
TP
Mean 27.08 20.77
SD 1.89 1.04
Min 22.48 17.57
Max 31.00 22.85
Table 113. Initial LiSi Block thicknesses’ mean, standard deviation, minimum and maximum values
When LS thicknesses were compared to each other, the LS-specimens with a
thickness of 1 mm showed a lower TP (mean = 20.77) than the 0.5 mm thick specimens
(mean = 27.08).
The Mann- Whitney U test revealed that the difference between thicknesses was
significant (p<0.001).
Figure 121. Boxplot of TP for each Initial LiSi Block thickness. *** (significant difference)
143
Figure 122. Initial LiSi Block specimens’ translucency after multiple firings
b. Initial LiSi Block 0.5 mm Firings
Firings Initial LiSi Block 0.5 mm
Mean SD Min Max
TP
B 27.41 1.80 24.21 30.63
1F 26.92 1.97 22.81 30.57
2F 26.84 1.90 22.73 30.03
3F 27.05 2.09 22.49 31.00
4F 27.17 1.76 23.91 30.42
5F 27.06 2.05 22.67 30.46
Table 114. Initial LiSi Block 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the LS 0.5 mm firings were compared to each other, 2F presented the lowest
TP (mean = 26.84), followed by 1F (mean = 26.92), 3F (mean = 27.05), 5F (mean =
27.06), and 4F (mean = 27.17). B presented the highest TP (mean = 27.41).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p=0.947).
Figure 123. Changes in TP between firings of 0.5 mm Initial LiSi Block specimens
20
21
22
23
24
25
26
27
28
B 1F 2F 3F 4F 5F
Initial LiSi Block 0.5 mm
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Figure 124. Initial LiSi Block 0.5 mm specimens’ translucency after multiple firings
c. Initial LiSi Block 1 mm Firings
Firings Initial LiSi Block 1 mm
Mean SD Min Max
TP
B 21.18 1.00 18.78 22.85
1F 20.67 1.09 17.76 22.37
2F 20.68 1.08 17.87 22.38
3F 20.64 1.06 17.81 22.54
4F 20.86 1.01 18.12 22.59
5F 20.61 1.08 17.57 22.33
Table 115. Initial LiSi Block 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the LS 1 mm firings were compared to each other, 5F presented the lowest
TP (mean = 20.61), followed by 3F (mean = 20.64), 1F (mean = 20.67), 2F (mean =
20.68), and 4F (mean = 20.86). B presented the highest TP (mean = 21.18).
The Kruskal-Wallis test revealed that the differences between firings were not
significant (p=0.389).
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Figure 125. Changes in TP between firings of 1 mm Initial LiSi Block specimens
Figure 126. Initial LiSi Block 1 mm specimens’ translucency after multiple firings
20
21
22
23
24
25
26
27
28
B 1F 2F 3F 4F 5F
Initial LiSi Block 1 mm
146
5.5.5 Amber Mill Comparisons
a. Amber Mill Thickness
Thickness Amber Mill
0.5 mm 1 mm
TP
Mean 38.11 27.42
SD 3.7 5.72
Min 28.59 17.17
Max 46.85 38.56
Table 116. Amber Mill thicknesses’ mean, standard deviation, minimum and maximum values
When AM thicknesses were compared to each other, the AM-specimens with a
thickness of 1 mm showed a lower TP (mean = 27.42) than the 0.5 mm thick specimens
(mean = 38.11).
The Mann- Whitney U test revealed that the difference between thicknesses was
significant (p<0.001).
Figure 127. Boxplot of TP for each Amber Mill thickness. *** (significant difference)
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Figure 128. Amber Mill specimens’ translucency after multiple firings
b. Amber Mill 0.5 mm Firings
Firings Amber Mill 0.5 mm
Mean SD Min Max
TP
B 37.46 2.37 34.66 30.63
1F 40.02 2.86 37.05 30.57
2F 41.17 2.94 38.36 30.03
3F 39.43 3.02 36.25 31.00
4F 32.06 2.90 32.11 30.42
5F 33.52 2.65 28.59 30.46
Table 117. Amber Mill 0.5 mm thickness’s mean, standard deviation, minimum and maximum values
When the AM 0.5 mm firings were compared to each other, 4F presented the
lowest TP (mean = 32.06), followed by 5F (mean = 33.52), B (mean = 37.46), 3F (mean
= 39.43), and 1F (mean = 40.02). 2F presented the highest TP (mean = 41,17).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference between B and 2F (p=0.019).
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Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
Amber Mill 0.5 mm
B-1F 0.531
B-2F 0.019
B-3F 1.000
B-4F 1.000
B-5F 0.096
Table 118. Pairwise comparison between firings
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
Figure 129. Changes in TP between firings of 0.5 mm Amber Mill specimens
Figure 130. Amber Mill 0.5 mm specimens’ translucency after multiple firings
15
20
25
30
35
40
45
B 1F 2F 3F 4F 5F
Amber Mill 0.5 mm
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c. Amber Mill 1 mm Firings
Firings Amber Mill 1 mm
Mean SD Min Max
TP
B 30.69 0.96 29.53 33.07
1F 35.07 1.44 33.39 38.56
2F 31.04 1.36 29.48 33.99
3F 26.55 1.85 24.08 29.22
4F 21.99 1.88 19.86 24.75
5F 19.17 1.70 17.17 21.77
Table 119. Amber Mill 1 mm thickness’s mean, standard deviation, minimum and maximum values
When the AM 1 mm firings were compared to each other, 5F presented the lowest
TP (mean = 19.17), followed by 4F (mean = 21.99), 3F (mean = 26.55), B (mean = 30.69),
and 2F (mean = 31.04). 1F presented the highest TP (mean = 35.07).
The Kruskal-Wallis test revealed that the differences between firings were
significant (p<0.001).
The results of the pairwise Mann-Whitney comparisons showed that there was a
significant difference between B and 4F (p=0.001), and B and 5F (p=0.000).
Pairwise Comparisons of Firings
Material Thickness Firings Adj. Sig.
*
Amber Mill 1 mm
B-1F 0.243
B-2F 1.000
B-3F 0.273
B-4F 0.001
B-5F 0.000
Table 120. Pairwise comparison between firings
*Significance values have been adjusted by the Bonferroni correction for multiple tests.
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Figure 131. Changes in TP between firings of 1 mm Amber Mill specimens
Figure 132. Amber Mill 1 mm specimens’ translucency after multiple firings
5.6 Pre-Crystallized and Crystallized Specimens
As mentioned above, EX and AM blocks come with lithium metasilicate crystals and
require a crystallization firing after milling, in order to convert them into lithium
disilicate. This leads to a visual change of color from the purple color in the blue stage to
a tooth-colored appearance. It also goes along with a increase in translucency (EX).
For AM, the block is delivered as a highly translucent material, which changes to a
tooth-colored appearance and decreases in translucency during crystallization.
The ΔE00 and the TP of these specimens before crystallization was also measured.
Even if the results were not statistically analyzed, it is worth mentioning the differences.
15
20
25
30
35
40
45
B 1F 2F 3F 4F 5F
Amber Mill 1 mm
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EX Pre-crystallized to crystallized specimens
Mean SD Min Max
0.5 mm ΔE00 1.14 0.04 1.05 1.21
1.0 mm ΔE00 1.64 0.07 1.50 1.73
Table 121. EX pre-crystallized to crystallized specimens ΔE00 mean, standard deviation, minimum and maximum
values
EX Pre-crystallized specimens
Mean SD Min Max
0.5 mm TP 8.66 0.36 8.07 9.29
1.0 mm TP 3.69 0.24 3.20 4.04
Table 122. EX pre-crystallized specimens TP mean, standard deviation, minimum and maximum values
For EX 0.5 mm specimens, the ΔE00 from the pre-crystallized to the crystallized
specimens was 1.14, and for the 1 mm specimens it was 1.64.
The TP for EX pre-crystallized 0.5 mm specimens was 8.66, showing that the
translucency was low compared to the TP of the crystallized specimens which was 27.34.
For the 1 mm pre-crystallized specimens, the TP was 3.69, showing also a lower
translucency compared to crystallized specimens which presented a TP of 19.52. (Figure
133).
Figure 133. Pre-crystallized and crystallized EX specimens
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AM Pre-crystallized to crystallized Specimens
Mean SD Min Max
0.5 mm ΔE00 4.13 1.54 2,54 7.30
1.0 mm ΔE00 5.17 0.81 4.40 7.17
Table 123. AM pre-crystallized to crystallized specimens ΔE00 mean, standard deviation, minimum and maximum
values
AM Pre-crystallized Specimens
Mean SD Min Max
0.5 mm TP 48.84 6.64 43.21 60.67
1.0 mm TP 44.64 4.64 40.96 55.89
Table 124. AM pre-crystallized specimens TP mean, standard deviation, minimum and maximum values
For AM 0.5 mm specimens the ΔE00 from the pre-crystallized to the crystallized
specimens was 4.13, and for the 1 mm specimens it was 5.17.
The TP for AM pre-crystallized 0.5 mm specimens was 48.84 showing that the
translucency was very high compared to the TP of the crystallized specimens which was
37.4. For the 1 mm pre-crystallized specimens the TP was 44.64, also showing a high
translucency compared to the crystallized specimens which showed a TP value of 30.69
(Figure 134). Still these changes are not as evident as the ones of the EX material,
specially in terms of shade.
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Figure 134. Pre-crystallized and crystallized AM specimens. Black background shows a clearer difference in
translucency
154
6. Discussion:
6.1 Color Change
The first null hypothesis (multiple firings do not affect the color of the different
lithium disilicate CAD-CAM materials). was rejected since multiple firings did influence
the color of the specimens.
The second null hypothesis (the thickness of the material does not affect the color
of the different lithium disilicate CAD-CAM specimens after multiple firings) was
rejected because the thickness of NC, LS and AM did affect the color of the specimens.
The third null hypothesis (different lithium disilicate CAD-CAM materials do not
affect the color of the specimens after multiple firings) was rejected since EX, NC and
AM did experience a significant change in color after multiple firings.
6.1.1 Devices and Color Systems
According to the literature, a ΔE00 of 3.7 is acceptable in the mouth since the light
incidence is limited, and a ΔE00 of less than 2 is considered excellent esthetics (104).
Our study showed that AM will be the only material in which the color change will not
be clinically acceptable (ΔE=5.33), and all the other materials will have excellent
esthetics (ΔE<2).
In our study it was decided to use a spectrophotometer to analyze changes in color
and in translucency for multiple reasons. These devices are 33% more accurate and obtain
a more objective match in 93.3% of the cases compared to the visual method. This devices
have an integrated light and therefore are not affected by the ambient light (120,124),
contrary to digital cameras where the flashes and different settings could have affected
the shade of the specimen and therefore the results (126). Spectrophotometers where also
preferred over colorimeters because colorimeters do not register spectral reflectance,
which makes them less accurate than spectrophotometers, and also they only measure the
light in the green, blue, and red areas of the visible spectrum (126), while
spectrophotometers use the entire light spectrum. Spectrophotometers where also
preferred over scanners, since scanners can only analyze color, based on the VITA shade
guide, and cannot measure L*, a*, and b* values (117), which are necessary to calculate
the color change.
When reviewing the literature, different studies used different spectrophotometers
to evaluate changes in color and translucency. CM 2600D (132,133), VITA Easyshade
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(104), and Spectroshade Micro II (142). In our study it was decided to use the Crystaleye
Spectrophotometer because the literature has shown that among the different
spectrophotometers available in the market, the Crystaleye was the most precise in both
lighted and darkened rooms (14).
De Moraise et al. (133)analyzed EX specimens with a thickness of 1.35 mm after
five and seven firings. This study did not show any significant change in color in their
specimens (133). In our study the 1 mm thick EX specimens did experience a significant
change in color after the fifth firing. This difference in results might be attributed to the
different formulas used to calculate the ΔE. De Moraise et al. (133) used the ΔE formula
to calculate the color change. In our study the ΔE00 formula was used, which is more
sophisticated and computationally involved than its predecessor (99). Research has found
that the ΔE00 formula gives a better evaluation of the difference in color, providing better
indicator of human acceptability and perceptibility of color differences between teeth
(100,101).
6.1.2 Materials and Composition
In this study, all the materials that were evaluated were lithium disilicate
reinforced glass ceramic CAD/CAM materials. There was a significant difference in color
between the materials, this could be explained by the fact that every material has different
shapes and sizes of crystals. Research has shown that EX crystals are 1–1.5 μm long and
are composed of multiple sheet layers, NC crystals are 1 μm long, fine-grain needlelike
and are surrounded by large unattached glass matrix particles, and AM crystals are 0.2
μm (200 nm) long surrounded by large patches of glassy matrix (59). For LS, there is no
literature reporting its microstructure and crystal size, yet.
Out of the four materials, three experienced significant color change after multiple
firings. EX and NC 1 mm specimens presented a significant change in color after the fifth
firing. The AM 0.5 mm specimens presented a significant change in color after the third
firing and the AM 1 mm specimens presented a significant color change after the second
firing. Even though all products are made of lithium disilicate reinforced glass ceramic,
there are other factors that could contribute to these results. The changes in color might
be explained by the fact that during firing some of the pigments that are used in the
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different materials were able to replace regular octahedral or tetrahedral sites in the crystal
phases found in glass-ceramics, generating the color changes (42,53).
Rare earth ions like Nd3+ have the ability to stay in the glassy matrix and therefore
they do not produce color changes in the glass ceramic. On the other hand, d-element ions
are the pigments that are capable of substituting the octahedral and tetrahedral sites in the
crystal phases and therefor are the responsible ones for color changes. The type and
concentration of pigments in glass-ceramic materials is up to each manufacturer and the
shade that they which to achieve (53). Another explanation for these changes is that some
of the metal oxides (f-element and d-element oxides) used in each material can become
unstable after several firings, suffering from pigment breakdown generating a color
change in the ceramics, still it is not know the type and concentration of this oxides
necessary to generate a color change (53,85,86,143,144). For the materials tested in this
study, none of the manufacturers disclose the type and concentration of metal oxides used
in their products, therefore it was not possible to determine which of the oxides could be
responsible for these changes (61–63,135).
AM specimens showed a different result compared to the other materials. Not only
did the color changed, but the specimens exhibit a spotted pattern Figure 135. Since the
manufacturers did not display which specific color oxides are used in their products, it is
not possible to determine which of these components are responsible for this result, it
seems that some of the oxides have experienced pigment breakdown which has caused
this specific pattern in the specimens. Another explanation for these results might be
related to an uneven distribution of the crystals and glass matrix inside of the material.
This uneven distribution might be the responsible for areas being more opaque (crystal
accumulation), and areas being more translucent (areas with more glass matrix), as
indicated by the arrows in Figure 135.
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Figure 135. Spotted pattern exhibited by AM specimens after multiple firings. Black arrow: opaque areas; White
arrow: translucent areas
To the date there are not many studies that have evaluated the color of different
lithium disilicate reinforced glass ceramic CAD materials after multiple firings. Most of
the studies have compared e.max to zirconia reinforced lithium silicate (131,133), or
pressed lithium disilicate with milled lithium disilicate (104).
De Moraise et al. (133) evaluated the color stability of EX and Vita Suprinity,
after seven firings and showed that there was a slight difference between the fifth and the
seventh firing, still this difference was not significant for both materials, showing that
even though the zirconia reinforced lithium silicate has a different composition, this
composition does not affect the color stability of the material (133).
Even if in our study pressed lithium disilicate reinforced glass ceramics were not
evaluated, it is important to mention what possible difference could be found when using
this type of material. Ozturk et al. (104) evaluated the change in color of IPS e.max Press
after 3, 5 and 9 firings. They used three different thicknesses (0.5, 1, and 1.5 mm). This
study did not find any significant difference between the firings which is similar to our
results for the 0.5 mm specimens (104). Contrary to their study, our study did find a
significant difference in color after the fifth firing in the EX 1 mm specimens. The
difference in results might be caused by the fact that Ozturk et al. (104) did not measure
the color at the baseline. Another difference between our study and theirs is that they
reached ∆E values of higher than two, which differs from our study, where the ∆E values
for EX regardless of their thicknesses did not reach 1. This could be explained by the fact
the IPS e.max Press has larger crystal size that IPS e.max CAD (59), this affects the
translucency of the material which has an influence on the final color. In this study it was
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not disclosed what shade and what translucency of the material was used, which could
have also influenced the results.
6.1.3 Firings
As shown in the results, all materials presented a non-homogeneous distribution
of the lithium disilicate crystals in the glassy matrix. In some materials (AM, LS) this was
very obvious and could be easily observed with the naked eye, while in others (EX, NC)
it was noticed only under higher magnification. As the number of firings increased, this
non homogeneity became more evident. This happens because the crystal interlocking
increases with the number of firings (84). If the crystal distribution is not even, the areas
that are occupied only by glassy matrix will become bigger, as the interlocking becomes
tighter (84). This effect was most noticeable in the AM specimens, with large swirls and
patches of darker/ligher areas as well as more opaque/translucent areas. On the other
hand, LS specimens showed an increased opacity only along the margins of the
specimens, this could be explained by a higher crystal concentration in this area. Overall,
this material did not show any color change during the firings, because the margin areas
were not read by the spectrophotometer for measurement. Still is important to take it
under consideration since it can affect the final outcome of the restoration. EX and NC
also showed a non-uniform color and translucency distribution, but with visually less
perceivable swirls and patches, showing a better distribution of the crystals in the glassy
matrix. This might be even less noticeable in a restoration.
Miranda et al. (132) evaluated the change in color of EX 1.2 mm specimens after
two, four, and six firings. They found that there was a significant difference in the ΔE00
between the second and fourth firing and the ΔE00 between the second and sixth firing,
when no stains or glaze were used (132). These results are similar to the ones found in
our study where the EX 1 mm specimens did experience a significant difference between
the baseline and the fifth firing. Still, Miranda et.al (132) did not measure the color at
baseline and also performed an extra firing than in our study.
De Moraise et al. (133) did not find any changes in their EX-specimens after seven
firings, but in our study we did find a significant difference in the EX 1 mm specimens
between the ∆E1 and the ∆E5. One of the explanations for this difference in results might
be that in their study (133) the baseline color was not evaluated.
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The only study that compared only lithium disilicate reinforced glass ceramic
CAD/CAM materials (EX, NC, and AM), evaluated the color change after two firings
and found that there were significant differences in the color (142). However, we were
not able to compare their results with ours. For this study, Jurado et al. did not used the
ΔE formula to calculate the color difference. They measured the color based on the VITA
shades, and they did not measure the L*, a* and b* values (142). Therefore, it is not
possible for us to do a direct comparison of their results with ours.
6.1.4 Thickness of the material
In our study, the overall comparison did not show any difference between the
material thickness regarding color change. Still in the individual comparisons of NC, LS,
and AM showed significant differences between the two thicknesses. One of the possible
explanations for these results might be that the thickness of each material influences their
translucency. The translucency of a material has an important influence the color of that
material as well (145). If the translucency of a material changes, so does the transmittance
of the light. Since color is measured by how the light is reflected and transmitted form an
object, then the light transmittance of an object will directly influence its shade (146). In
summary, the translucency of a material, and a direct effect on the color of such material,
this could explain why some materials experienced changes in color only on the thinner
specimens and not on the thicker ones or vice versa.
6.1.5 Staining and Glaze
Stains and glazes are used in the restorations to better mimic the natural teeth.
Usually all monolithic restorations undergo these procedures (79). Ceramic stains are
composed of metallic oxides of different shades (147). Their purpose is to modify the
shade of a restoration. Even tough stains and glazes are used for most of the monolithic
restorations, they were not used in this study. The reasoning behind not using stains and
glazes is that they affect the shade and the translucency of the ceramic, on the other hand,
adding a coat of any material on top of the ceramic also influences the surface roughness.
If the roughness of the surface changes, so does the way the light is transmitted and
scatter, which also influences the final shade of the material (148). Miranda et al. (132)
showed an increased in the surface roughness when stains and glaze were applied. The
aim of this study was to analyze the color and the translucency of the ceramic itself and
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not have it influenced by staining and glazing materials. It was considered that these
elements could affect the final outcome of the study and therefore they were not used.
6.2 CIE L*a*b*
6.2.1 Materials and Composition
AM showed the lowest L* values in both thicknesses and NC showed the highest
L* values in both thicknesses. AM showed the lowest a* values, and EX the highest. AM
showed the lowest b* values. and NC the highest.
6.2.2 Firings
EX did not show any significant difference in L*values for both thicknesses after
five firings. The 0.5 mm EX specimens showed a significant decrease in the a* values
between the baseline and the fifth firing which results in greener specimens, while the 1
mm specimens experienced a significant increase in the a* value, between the baseline
and the fifth firing, which results in redder specimens. For the b* values, EX 0.5 mm
specimens showed a significant increased between the baseline and the third firing and
between the baseline and the fifth firing which results in yellower specimens. The b*
values for the 1 mm specimens also increased significantly after the third firing.
NC 0.5 mm specimens became lighter (increase in the L* value) after the second
firing, and the 1 mm specimens also became lighter after the first firing. The a* values
for both thicknesses increased after the second firing which results in redder specimens.
The b* values increased for the 0.5 mm specimens after the fourth firing and for the 1
mm specimens after the second firing which results in yellower specimens.
NC did not show any significant difference in L*values for both thicknesses after
five firings. The a* values increased for the 0.5 mm specimens after the fifth firing, and
for the 1 mm specimens there was a significant increase in these values between the
baseline, first, second, and third firing, which resulted in redder specimens. On the other
hand, the b* values decreased in the 0.5 mm specimens after the fifth firing and in the 1
mm specimens after the first firing, resulting in bluer specimens.
AM experienced an increase in the L* values, for the 0.5 mm specimens this
change was significant after the fifth firing and for the 1 mm specimens after the fourth
firing, which resulted in lighter specimens. The 0.5 mm specimens experienced a decrease
in the a* values after the fourth firing (greener specimens), and the 1 mm specimens
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experienced an increase in the a* values after the fifth firing (redder specimens). The 0.5
mm specimens did not show any significant changes in the b* values after five firings,
while the 1 mm specimens became yellower (increase) after the fourth firing.
6.2.3 Thickness of the material
For all materials, the 0.5 mm specimens where darker (lower L* values) than the
1 mm specimens. This is explained by the fact that a black background was used for the
measurements, and the 0.5 mm being more translucent were more affected by the darker
background than the 1 mm specimens. Other studies have reported the same results (104).
EX and AM 1 mm specimens were greener (lower a*) than the 0.5 mm specimens,
while NC and LS 1mm specimens were redder (higher a*) than the 0.5 mm specimens.
For all materials, the 0.5 mm specimens were bluer (lower b*) than the 1 mm
specimens.
6.3 Translucency Change
The fourth null hypothesis (multiple firings do not affect the translucency of the
different lithium disilicate CAD-CAM materials) was rejected since multiple firings did
influence the translucency of the specimens.
The fifth null hypothesis (the thickness of the material does not affect the
translucency of the different lithium disilicate CAD-CAM specimens after multiple
firings) was rejected because the thickness of the material did affect the translucency of
the specimens.
The sixth null hypothesis (different lithium disilicate CAD-CAM materials do not
affect the translucency of the specimens after multiple firings) was rejected since NC and
AM did experience a significant change in translucency after multiple firings.
The material with the highest translucency was AM and the material with the
lowest translucency was NC.
6.3.1 Materials and Composition
In our study, out of the four evaluated materials, two of them experienced
significant changes in translucency after multiple firings (NC, AM). NC 1 mm specimens
experienced a significant decrease in translucency after the fourth and fifth firing. AM
0.5 mm specimens showed a significant increase in translucency after the second firing,
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which later decreased. While the 1mm specimens showed a significant decrease in the
translucency after the fourth and fifth firing.
In the literature, two studies also evaluated zirconia reinforced lithium silicate
specimens. One study presented a significant change in translucency, which decreased
between the second and fifth firing and increased between the fifth and seventh firing
(133). Another study reported that after three firings there was a significant decrease in
the translucency of this material (131). These changes in translucency are caused by two
factors. The first one is that lithium disilicate are more crystalline materials than the
reinforced lithium silicate (133). The second one is that the zirconia content in the
zirconia reinforced lithium silicate has been proven to have a negative impact in the
translucency of this type of ceramic (73).
6.3.2 Firings
A decrease in translucency could be explained by a more compact interlocking of
the crystals (84) making it optically more dense and therefore more opaque, which could
explain our results. As mentioned above, each material has a different shape, size, and
distribution of crystals, making the interlocking process different in each material. Other
tests could help identify how the interlocking occurs in each material. On the other hand,
AM is a material that has the ability to change its translucency depending on the firing
temperature. According to the manufacturer’s instructions, the translucency of these
material could be lowered by increasing the furnace temperature by 5ºC. They attribute
this characteristic to the fact that a higher heat-treatment temperature generates a more
coarse crystalline structure and increases the density of the crystals which will increase
the scatter of the light ray and decrease the translucency (135). To exclude this factor, in
our study the temperature was not modified. The changing variable was the number of
firings, which clearly showed that translucency decreased with increasing numbers of
firings, all of which were performed at the same temperature.
Another factor that could have affected the translucency results might be the
spotted pattern that the samples presented (Figure 135), which presented more opaque
areas that could affected the final readings.
All materials experienced a decrease in translucency with increased number of
firings. Still the AM 1 mm showed an increase in translucency after the second firing.
This could be explained by the fact that the material might not have achieved a full
crystallization during the crystallization cycle. The growth of the crystals might be totally
163
completed after the second firing, which increased the material’s translucency (87). After
the material was fully crystalized, the translucency decreased because of the explanations
pointed above.
De Moraise et al. (133) found a significant decrease in the translucency between
the fifth and seventh firing, again in this study the baseline translucency was not analyzed.
Still in our study we found a significant decrease in translucency between the baseline
and the fifth firing, and we might have gotten the same results if we have fired the
specimens seven times.
Nejatidanesh et al. (131) evaluated the translucency of 0.6 and 1 mm EX
specimens after three firings. Their results coincide with ours since there was not a
significant change in the EX-specimen’s translucency after three firings.
Miranda et al. (132) evaluated the translucency of EX 1.2 mm specimens after
two, four and six firings. They did find a significant increase in the translucency after the
sixth firing. These results do not coincide with ours, where EX specimens regardless of
their thickness did not experience any changes in translucency after the fifth firing. These
difference in results might have occur after the sixth firing since they also did not find
any significant difference after the fourth firing (132).
6.3.3 Thickness of the material
In our study the overall and individual comparisons showed that there was a
significant difference between the two thicknesses. Our results agree with other studies
that have demonstrated that an increased translucency is obtained by decreasing the
ceramic thickness (104,131,149). Translucency is a phenomenon in which the majority
of the light passing through is transmitted and the minority is scattered (150). When the
thickness of a material increases, there is a decrease in the amount of light that is
transmitted and an increase on the amount of light that is reflected, that is why thicker
specimens are less translucent than thinner ones.
6.3.4 Staining and Glaze
Miranda et al. (132) showed that EX specimens that have stains and glaze have a
lower translucency than specimens that did not have any characterization (132). This
might be caused by the different pigments that are part of the stains.
164
Even tough in our study only the color and translucency stability after multiple
firings were evaluated, it is worth mentioning that there are other factors that should also
influence our decision in terms of material selection, for example, the material’s strength.
Despite this property not being evaluated in our study, it is worth mentioning that during
the polishing of the specimens, six LS 0.5 mm specimens developed a crack which later,
lead to the fracture of the specimens (Figure 136). These specimens were later replaced
for new ones in order to reach the adequate number of specimens per group (n=15).
Polishing was very important in our study since any scratches on the surface will affect
the way light is reflected and therefore have an influence on the final shade (151–154).
We wanted to make sure that all specimens reflected the light the same way without any
alterations, that is why special care was taken in polishing the specimens. In a dental
setting polishing is just as important to achieve optimate results.
Figure 136. (a) LiSi Initial Block specimen with crack development. (b) Fractured LiSi Initial Block specimen
Other studies should be conducted to evaluate different shades and translucencies of
the materials. Other factors like, stump shade, staining and glazing, cement shade,
material’s strength and bond strength should be considered before selecting the adequate
material for tooth restoration.
165
7. Conclusions
Based on the findings and limitations of our in vitro study, the following conclusions
could be drawn for the tested lithium disilicate reinforced glass ceramic CAD/CAM
materials:
1. The number of firings affects the color of most materials, leading to an increase of
ΔE00.
2. The material thickness influences the color change after multiple firings, with the 1
mm specimens generally experiencing more changes than the 0.5 mm specimens.
3. Changes in color are material dependent with the largest changes occurring in AM,
NC, and EX.
4. With an increasing number of firings translucency decreases.
5. The thickness of the materials influences the translucency of the materials with 0.5
mm specimens being more translucent than 1 mm specimens.
6. Change of translucency is material dependent with AM and NC significantly
decreasing in translucency after multiple firings.
7. Within each individual CAD/CAM block, color and translucency are not
homogeneously distributed.
8. Clinical Significance
When fabricating CAD/CAM restorations from various lithium disilicate reinforced
glass ceramic materials, the choice of the material and its thickness is of importance since
each material behaves differently in terms of color and translucency after multiple firings.
To achieve restorations with excellent esthetics (Δ<2 and no change in TP), a
maximum number of firings is recommended:
EX four firings, NC three firings, LS five firings, and AM one firing.
However, uneven distribution of color and translucency within each individual block
might make a predictable esthetic outcome even more challenging.
166
9. Disclaimer:
The authors affirm that there are no conflicts of interest.
167
10. Funding
The current in vitro study was supported by the program of Advanced Operative and
Adhesive Dentistry (AOAD), Restorative Sciences, at Herman Ostrow School of
Dentistry of University of Southern California (USC).
168
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Abstract (if available)
Abstract
Aim: Assess the effect of multiple firings on the color and translucency of different lithium disilicate reinforced glass ceramic CAD-CAM materials with thicknesses of 0.5 mm and 1 mm.
Materials and Methods: A total of 160 specimens (length 14.00 mm x width 12.00 mm x with thicknesses of 0.5 mm and 1.0 mm) of 4 different A1, HT lithium-disilicate reinforced glass ceramic blocks, IPS e.max CAD (EX; IPS e.max CAD, Ivoclar Vivadent, Schaan, Liechtenstein), n!ce (NC; Straumann, Freiburg, Germany), Initial LiSi Block (LS; GC, Tokyo, Japan), and Amber Mill (AM; HASSBIO, Kangreung, Korea) were subjected to a crystallization firing following the manufacturer’s recommendation and then all specimens were fired five times according to their individual straining and glazing parameters. The color and translucency of each specimen was measured in white and black backgrounds after each firing. The color change (ΔE00), and the translucency parameter (TP) were calculated. Data was statistically analyzed by applying non- parametric tests with ⍺=0.05.
Results: For ΔE00, overall comparisons showed significant differences between materials, except for NC and LS, which were not different from each other (p>0.05). EX (p=0.013) and NC (p<0.001) 1 mm specimens increased significantly after the fifth firing. AM 0.5 mm specimens increased significantly (p=0.001) after the third firing and AM 1 mm specimens increased significantly (p=0.000) after the second firing. For TP, overall comparisons showed significant differences between materials (p<0.001). TP in 0.5 mm specimens was higher than in 1 mm specimens (p<0.001). For NC, TP decreased after the fourth (p=0.008) and fifth (p=0.033) firing in 0.5 mm specimens, and after the fourth (p=0.004) and fifth (p=0.000) firing for 1 mm specimens. For AM, 0.5 mm thickness, TP increased after the second firing (p=0.019) but decreased in 1 mm specimens after the fourth (p=0.001) and fifth (p=0.000) firing.
Conclusions: Multiple firings influence the color and translucency of different lithium disilicate reinforced glass ceramic CAD/CAM materials, however, the changes might affect the materials differently. Most of the thicker specimens experienced more pronounced color changes (ΔE00); translucency decreases with increasing thickness of the material. Within the CAD/CAM block, color and translucency are non-homogeneous
Clinical Significance: Differences in color and translucency of different lithium disilicate reinforced glass ceramic CAD/CAM materials as well as the thickness of the restoration must be considered when subjecting them to multiple firings. To achieve restorations with excellent esthetics (ΔE00<2 and no change in TP), a maximum number of firings is recommended: EX four firings, NC three firings, LS five firings, and AM one firing. However, uneven distribution of color and translucency within each individual block might make a predictable esthetic outcome even more challenging.
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Ramirez Goercke, Andrea Paola
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Effect of repeated firing on color and translucency of different CAD/CAM lithium disilicate reinforced glass-ceramic materials
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School of Dentistry
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Biomaterials and Digital Dentistry
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2022-12
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