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Wear resistance analysis of additively manufactured materials for permanent restorations.

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Wear resistance analysis of additively manufactured materials for permanent restorations.

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Content Wear resistance analysis of addi0vely manufactured materials for permanent restora0ons
By
Jordi Llena Prats, DDS
A Thesis Presented to the
FACULTY OF THE USC HERMAN OSTROW SCHOOL OF DENTISTRY
UNIVERSITY OF SOUTHERN CALIFORNIA
In Par0al Fulfillment of the
Requirement for the Degree
MASTER OF SCIENCE
(BIOMATERIALS AND DIGITAL DENTISTRY)
December 2023

Copyright 2023 Jordi Llena Prats

ii
Dedica'on

To my parents, Nuria Prats and Oriol Llena, who have always supported me with their
uncondi0onal love. To my brother MarW and my sister Maria. To my family of den0sts in
Barcelona with who I share my passion for this profession. To my family of friends in the United
States who have been there since the first day I set foot in this country cheering for my success.
I will always be grateful for all your support.

iii
Acknowledgments

I am profoundly grateful to Dr. Jin-Ho Phark, my advisor, for the invaluable assistance and
support he provided in guiding me through the comple0on of my thesis, as well as for the
significant amount of 0me he dedicated. His extensive knowledge and guidance were crucial
in helping me finish my thesis, and I appreciate all his contribu0ons and insights that he made.
To my co-advisor, Dr. Sillas Duarte, my deep gra0tude for your support, dedica0on, and love
for the profession. I am grateful I have had the 0me to share our passion for den0stry and
innova0on, for your mo0va0on in the most important moments and your uncondi0onal help
throughout the advanced opera0ve program and master.
I would like to thank my faculty members throughout my training in the Advanced Opera0ve
and Adhesive Den0stry program, Dr. Alena Knezevic, Dr. Eddie Sheh, and Dr. Jenny Son. My
journey through the specialty program would not have been the same without your help and
knowledge.
I would like to acknowledge the program specialist, Ms. Karen Guillen, who has been a
fundamental individual through my stay at USC helping me being a more organized person and
making sure that we were always doing well.
Not to forget my gra0tude for my coresident Dr. Waad Mzain, with who I spent 2 years of my
life sharing our love for den0stry.

iv
Table of contents
Dedica'on................................................................................................................................................................... ii
Acknowledgments......................................................................................................................................................iii
List of Tables.............................................................................................................................................................viii
List of Figures ..............................................................................................................................................................x
Abstract.....................................................................................................................................................................xiii
Chapter 1: Introduc'on ............................................................................................................................................. 1
1.1. Digital den'stry & history........................................................................................................................ 1
1.2. Restora've den'stry................................................................................................................................ 1
1.3. How the cad / cam process works........................................................................................................... 2
1.3.1. Scanning technologies................................................................................................................... 3
1.3.2. SoKware & design.......................................................................................................................... 7
1.3.3. Manufacturing methods................................................................................................................ 8
1.3.3.1. Subtrac've manufacturing ............................................................................................................ 8
1.3.3.2. Addi've manufacturing ................................................................................................................. 9
1.4. Materials................................................................................................................................................ 10
1.4.1. Metals .......................................................................................................................................... 10
1.4.2. Ceramics....................................................................................................................................... 11
1.4.2.1. 3D prin'ng ceramics.................................................................................................................... 13
1.4.3. Polymers....................................................................................................................................... 14
1.4.3.1. Types of polymers........................................................................................................................ 14
1.4.3.1.1. Acrylic Resins................................................................................................................................ 14
1.4.3.1.2. PEEK.............................................................................................................................................. 15
1.4.3.1.3. Composite resins.......................................................................................................................... 15
1.4.3.1.4. Other polymers............................................................................................................................ 16
1.4.3.2. Ini'ators - Polymeriza'on............................................................................................................. 17

v
1.4.3.3. Fillers............................................................................................................................................ 19
1.4.3.4. Coupling agents ........................................................................................................................... 21
1.4.3.5. Manufacturing methods for indirect polymer restora'ons........................................................ 22
1.5. Mechanical proper'es of the materials................................................................................................ 26
1.5.1. Strength........................................................................................................................................ 26
1.5.2. Toughness .................................................................................................................................... 26
1.5.3. Edge Strength / Chipping ............................................................................................................. 27
1.5.4. Fa'gue resistance ........................................................................................................................ 27
1.5.5. Elas'c modulus............................................................................................................................ 27
1.5.6. Wear............................................................................................................................................. 27
1.5.6.1. Types of wear and classifica'on .................................................................................................. 28
1.5.6.2. Clinical wear & natural den''on................................................................................................. 30
1.5.6.3. Clinical research of wear.............................................................................................................. 33
1.5.6.4. In vitro research of wear.............................................................................................................. 33
1.5.6.5. Wear simulators........................................................................................................................... 34
1.5.6.6. Correla'on in vitro – clinical........................................................................................................ 36
1.6. Objec've................................................................................................................................................ 38
1.7. Aim......................................................................................................................................................... 38
1.8. Null hypothesis ...................................................................................................................................... 38
Chapter 2: Materials and methods......................................................................................................................... 39
2.1. Study design........................................................................................................................................... 39
2.2. Sample fabrica'on................................................................................................................................. 41
2.2.1. Subtrac've manufactured material............................................................................................. 41
2.2.2. Addi'vely manufactured material:.............................................................................................. 42
2.2.3. Polishing ....................................................................................................................................... 47
2.2.4. Interchangeable moun'ng system.............................................................................................. 47
2.2.5. Antagonists................................................................................................................................... 50

vi
2.3. Wear simulator ...................................................................................................................................... 53
2.4. Volumetric loss and ver'cal loss data acquisi'on for the samples and antagonists............................ 54
2.5. Volumetric loss analysis......................................................................................................................... 56
2.6. Ver'cal loss analysis .............................................................................................................................. 57
2.7. Cross-Sec'on analysis with Profilometry .............................................................................................. 59
2.8. Sample and document iden'fica'on .................................................................................................... 60
2.9. Sta's'cs................................................................................................................................................. 64
Chapter 3: Results.................................................................................................................................................... 66
3.1. Images of the op'cal scans ................................................................................................................... 66
3.2. Images of the profilometry aKer 120,000 cycles.................................................................................. 68
3.3. Descrip've analysis of the Volumetric Loss of the samples................................................................. 72
3.3.1. Data normality analysis and equality of variances of volumetric loss........................................ 74
3.4. Comparison between materials............................................................................................................ 75
3.4.1. Volumetric loss between different materials.............................................................................. 75
3.4.2. Volumetric loss between different materials aKer 120,000 cycles ............................................ 78
3.5. Comparison between cycles.................................................................................................................. 80
3.5.1. Volumetric loss depending on cycles for all materials. ............................................................... 80
3.5.2. Volumetric loss depending on cycles for LAVA ULTIMATE .......................................................... 82
3.5.3. Volumetric loss depending on cycles for VARSEOSMILE CROWN PLUS...................................... 84
3.5.4. Volumetric loss depending on cycles for CERAMIC CROWN ...................................................... 86
3.6. Comparison between chambers ........................................................................................................... 88
3.6.1. Volumetric loss between chambers for all materials.................................................................. 88
3.7. Descrip've analysis of the Ver'cal Loss of the samples....................................................................... 90
3.7.1. Data normality analysis and Equality of variances of ver'cal loss.............................................. 92
3.8. Comparison between materials............................................................................................................ 93

vii
3.8.1. Ver'cal loss between different materials.................................................................................... 93
3.8.2. Ver'cal loss between different materials aKer 120,000 cycles.................................................. 95
3.8.3. Ver'cal loss of the antagonist between different materials....................................................... 97
3.9. Descrip've analysis of the Ver'cal Loss: Profilometry horizontal/ver'cal cross-sec'on .................... 99
3.9.1. Data normality analysis/Equality of variances of ver'cal loss -profilometry ............................101
3.9.2. Ver'cal loss of the antagonist between different materials Horizontal cross-sec'on.............102
3.9.3. Ver'cal loss of the antagonist between different materials Ver'cal cross-sec'on..................104
Chapter 4: Discussion ............................................................................................................................................106
4.1. Materials..............................................................................................................................................106
4.1.1. LAVA ULTIMATE ..........................................................................................................................108
4.1.2. VARSEOSMILE CROWN PLUS .....................................................................................................110
4.1.3. CERACMIC CROWN....................................................................................................................112
4.1.4. EMPRESS CAD ............................................................................................................................115
4.1.5. Comparison to other materials .................................................................................................116
4.2. Ver'cal loss – volumetric loss difference. ...........................................................................................117
4.3. Quan'fica'on ......................................................................................................................................118
4.4. Method ................................................................................................................................................120
4.5. Other considera'ons...........................................................................................................................121
Chapter 5: Conclusions..........................................................................................................................................122
References..............................................................................................................................................................123

viii
List of Tables
Table 1 Classifica'on of resin based dental composites (95) ..................................................................................... 21
Table 2: Materials composi'on................................................................................................................................. 40
Table 3: Iden'fica'on codes used for the samples.................................................................................................. 60
Table 4: Iden'fica'on codes used for the antagonists............................................................................................. 60
Table 5: File names used for Lava Ul'mate STL files ................................................................................................ 61
Table 6: File names used for Ceramic Crown STL files.............................................................................................. 62
Table 7: File names used for VarseoSmile Crown Plus STL files................................................................................ 62
Table 8: File names used for Lava Ul'mate Antagonists STL files ............................................................................ 63
Table 9: File names used for Ceramic Crown Antagonists STL files.......................................................................... 63
Table 10: File names used for VarseoSmile Crown Plus Antagonists STL files.......................................................... 64
Table 11: Overall volumetric loss (mm3
) of Lava Ul'mate, VarseoSmile Crown Plus and Ceramic Crown.............. 73
Table 12: Shapiro-Wilk test for the Volumetric loss (normality) .............................................................................. 74
Table 13: Levene's test (equality of variances)......................................................................................................... 74
Table 14: Overall material mean, standard devia'on, maximum and minimum values ......................................... 75
Table 15: Overall pairwise comparison between materials...................................................................................... 76
Table 16: Material mean, standard devia'on, maximum and minimum for volumetric loss.................................. 78
Table 17: Overall Pairwise comparison between materials at 120,000 cycles......................................................... 79
Table 18: Mean, Standard devia'on, maximum and minimum from cycles volumetric loss. ................................. 80
Table 19:Overall pairwise comparison between cycles............................................................................................ 81
Table 20: Mean, Standard devia'on, maximum and minimum from cycles volumetric loss. ................................. 82
Table 21: Overall pairwise comparison between cycles........................................................................................... 83
Table 22: Mean, Standard devia'on, maximum and minimum from cycles volumetric loss. ................................. 84
Table 23: Overall pairwise comparison between cycles........................................................................................... 85
Table 24: Mean, Standard devia'on, maximum and minimum from cycles volumetric loss. ................................. 86
Table 25: Overall pairwise comparison between cycles........................................................................................... 87
Table 26: Mean, Standard devia'on, maximum and minimum from chamber volumetric loss. ............................ 88
Table 27: Overall pairwise comparison between chambers..................................................................................... 89

ix
Table 28: Overall Ver'cal loss (µm) of Lava Ul'mate, VarseoSmile Crown Plus and Ceramic Crown ..................... 91
Table 29: Shapiro-Wilk test for the Ver'cal loss (normality).................................................................................... 92
Table 30: Levene's test (equality of variances)......................................................................................................... 92
Table 31: Mean, standard devia'on, maximum and minimum ver'cal loss (µm)................................................... 93
Table 32: Overall Pairwise comparison between materials at 120,000 cycles for ver'cal loss............................... 94
Table 33: Overall material mean, standard devia'on, maximum and minimum values for ver'cal loss (µm)....... 95
Table 34: Overall pairwise comparison between materials at 120,000 cycles ........................................................ 96
Table 35: Mean, Standard devia'on, maximum and mínimum from antagonists ver'cal loss (µm)...................... 97
Table 36: Overall pairwise comparison between antagonists.................................................................................. 98
Table 37: Overall Ver'cal loss (µm) of Lava Ul'mate, VarseoSmile Crown Plus and Ceramic Crown ..................... 99
Table 38: Ver'cal loss (µm) Lava Ul'mate, VarseoSmile Crown Plus, Ceramic Crown Ver'cal cross-sec'on.......100
Table 39: Shapiro - Wilk test for normality ..............................................................................................................101
Table 40: : Levene's test (equality of variances) Horizontal Cross-sec'on.............................................................101
Table 41: : Levene's test (equality of variances) Ver'cal Cross-Sec'on.................................................................101
Table 42: Mean, Standard devia'on, maximum and mínimum from ver'cal los horizontal cross-sec'on. .........102
Table 43: : Overall pairwise comparison between materials..................................................................................103
Table 44: Mean, Standard devia'on, maximum and mínimum from ver'cal los horizontal cross-sec'on ..........104
Table 45: Overall pairwise comparison between materials....................................................................................105

x
List of Figures
Figure 1: Digital Workflow........................................................................................................................................... 3
Figure 2: Intraoral scanner 'p..................................................................................................................................... 6
Figure 3: Classifica'on of dental ceramics................................................................................................................ 13
Figure 4: Classifica'on of photo ini'ators ................................................................................................................ 18
Figure 5: Classifica'on of tooth colored dental materials........................................................................................ 25
Figure 6: Abrasive wear classifica'on ....................................................................................................................... 28
Figure 7: Adhesive wear............................................................................................................................................ 29
Figure 8: Fa'gue wear............................................................................................................................................... 29
Figure 9: Corrosive wear ........................................................................................................................................... 30
Figure 10: IsoMet Precision Saw............................................................................................................................... 41
Figure 11: Lava Ul'mate CAD / CAM block measurements..................................................................................... 41
Figure 12: Lava Ul'mate Block.................................................................................................................................. 41
Figure 13: Es'ma'on of samples per block.............................................................................................................. 42
Figure 14:STL file of the sample for prin'ng............................................................................................................. 42
Figure 15: VarseoSmile Crown Plus bolle ................................................................................................................ 43
Figure 16: Slicing program (RayWare) before sending the job to the printer VarseoSmile Crown Plus.................. 43
Figure 17: 3D Printed VarseoSmile Crown Plus ........................................................................................................ 44
Figure 18: Addi've manufacturing workflow ........................................................................................................... 45
Figure 19: Ceramic Crown bolle .............................................................................................................................. 45
Figure 20: Sliceing program (RayWare) before sending the job to the printer Ceramic Crown.............................. 46
Figure 21: Ceramic Crown sample before removal of the supports ........................................................................ 46
Figure 22: Interchangeable moun'ng system .......................................................................................................... 48
Figure 23: Sample moun'ng to the interchangeable system................................................................................... 48
Figure 24: Indenta'ons on the surface of the samples to facilitate scanning and overlapping.............................. 49
Figure 25: Scanning plamorm .................................................................................................................................... 50
Figure 26:STL file of the antagonist........................................................................................................................... 50
Figure 27: Empress CAD Mul' .................................................................................................................................. 51

xi
Figure 28: Antagonist manufacturing process.......................................................................................................... 52
Figure 29: Empress CAD antagonist mounted in the chewing simulator mount..................................................... 52
Figure 30: dual-axis chewing simulator (CS-8, SD Mechatronic, Feldkirchen-Westerham, Germany).................... 53
Figure 31: Scanning sequence of the samples ......................................................................................................... 55
Figure 32: Scanning sequence of the antagonist...................................................................................................... 55
Figure 33: Cleaning process of original open mesh STL file to final closed STL file ................................................. 56
Figure 34: Volumetric loss analysis example ............................................................................................................ 57
Figure 35: GOM Inspect Overlap and deepest point selec'on ................................................................................ 58
Figure 36: Cross sec'on profilometry....................................................................................................................... 59
Figure 37: Images of the STL files of Lava Ul'mate.................................................................................................. 66
Figure 38: Images of the STL files of VarseoSmile Crown Plus................................................................................. 67
Figure 39: Images of the STL files of Ceramic Crown ............................................................................................... 68
Figure 40: Profilometry for Lava Ul'mate................................................................................................................. 69
Figure 41: Profilometry for VarseoSmile Crown Plus................................................................................................ 70
Figure 42: Profilometry for Ceramic Crown.............................................................................................................. 71
Figure 43: Overall mean volumetric loss (mm3)....................................................................................................... 72
Figure 44: Independent-Samples Kruskal-Wallis Test for Materials......................................................................... 75
Figure 45: Pairwise comparison of the materials volumetric loss............................................................................ 76
Figure 46: STL file from Ceramic Crown showing material ar'fact. ......................................................................... 77
Figure 47: Ceramic Crown profilometry ................................................................................................................... 77
Figure 48: Independent-Samples Kruskall-Wallis Test.............................................................................................. 78
Figure 49: Pairwise comparison between materials at 120,000 cycles ................................................................... 79
Figure 50: Independent-samples Kruskall-Wallis Test .............................................................................................. 80
Figure 51: Pairwise comparison between different cycles....................................................................................... 81
Figure 52: Independent-samples Kruskall-Wallis Test .............................................................................................. 82
Figure 53: Pairwise comparison between different cycles....................................................................................... 83
Figure 54: Independent-samples Kruskall-Wallis Test .............................................................................................. 84
Figure 55: Pairwise comparison between different cycles....................................................................................... 85
Figure 56: Independent-samples Kruskall-Wallis Test .............................................................................................. 86

xii
Figure 57: Pairwise comparison between different cycles....................................................................................... 87
Figure 58: Independent-samples Kruskall-Wallis Test .............................................................................................. 88
Figure 59: Pairwise comparison between different cycles....................................................................................... 89
Figure 60: Overall mean ver'cal loss (µm) ............................................................................................................... 90
Figure 61: Independent-Samples Kruskal-Wallis Test Ver'cal loss........................................................................... 93
Figure 62: Pairwise comparison between the different materials. .......................................................................... 94
Figure 63: Independent-Samples Kruskall-Wallis Test.............................................................................................. 95
Figure 64: Pairwise comparison between the different materials at 120,000 cycles.............................................. 96
Figure 65: Independent-samples Kruskall-Wallis Test .............................................................................................. 97
Figure 66: Pairwise comparison between materials and antagonists...................................................................... 98
Figure 67: Overall Ver'cal loss (µm) of Lava Ul'mate, VarseoSmile Crown Plus and Ceramic Crown.................... 99
Figure 68: Ver'cal loss (µm) Lava Ul'mate, VarseoSmile Crown Plus, Ceramic Crown ver'cal cross-sec'on .....100
Figure 69: : Independent samples Kruskall-Wallis Test...........................................................................................102
Figure 70: Overall pairwise comparison between materials..................................................................................103
Figure 71: Independent samples Kruskall-Wallis Test.............................................................................................104
Figure 72: Overall pairwise comparison between materials..................................................................................105
Figure 73: Horizontal profilometry of Lava Ul'mate aKer 120,000 cycles ............................................................109
Figure 74: Horizontal profilometry of VarseoSmile Crown Plus aKer 120,000 cycles............................................111
Figure 75: Horizontal profilometry of Ceramic Crown aKer 120,000 cycles..........................................................114

xiii
Abstract

Purpose: To evaluate the two-body wear of three CAD / CAM resin based permanent dental
materials (subtrac0ve: Lava Ul0mate; addi0ve: VarseoSmile Crown Plus, Ceramic Crown)
against a ceramic material (Empress CAD) using a two-axis chewing simulator.

Material and Methods: 24 samples were fabricated with 8 samples per group for the 3
different materials. The samples were fabricated and standardized by polishing the top surface.
Then, they were acached to an interchangeable moun0ng system to ease the posi0oning of
the samples during surface analysis. Dual-axis chewing simulator (CS-8, SD Mechatronic,
Feldkirchen-Westerham, Germany) was used for 120,000 cycles, applying 5kg on each bar with
a 0.7mm sliding movement at a frequency of 1.6Hz in dis0lled water. The samples and the
antagonists were analyzed with a surface op0cal scanner to evaluate volumetric loss and
maximum wear depth at different stages of the process. Addi0onally, profilometry was
performed on the samples aher 120,000 cycles.
Data was analyzed using nonparametric tests: Kruskal-Wallis Test (α=0.05) with Bonferroni posthoc test.
Results: Volumetric loss and ver0cal loss differed between materials (Ceramic Crown <
Lava Ul0mate < VarseoSmile Crown Plus). A sta0s0cally significant difference between Ceramic
Crown and the other two materials was shown. The number of cycles also showed an increase
of wear as the number of cycles increased.

xiv
Conclusions: The wear of defini0ve milled and printed CAD/CAM materials is material and
wear cycle dependent. The material with the larger filler par0cles showed less wear than the
other two materials. Wear increases with increasing numbers of cycles.

1
Chapter 1: Introduc'on
1.1. Digital den-stry & history
The beginning of digital den0stry applied to restora0ve den0stry can be acributed to Mörmann
and Brandes0ni with the introduc0on of the CEREC system in 1985.
(1) Ever since, digital
den0stry has been exponen0ally innova0ng with scanning systems, and manufacturing
methods.
(2) This new methods of manufacturing, both addi0ve and subtrac0ve allow for fast
and precise produc0on with no need of physical models.
(3) This newer methods of fabrica0on
and design allowed for a broad of new long las0ng esthe0c treatments and approaches to
restora0ve den0stry.
(4) Some of this new approaches to restora0ve den0stry are related to
chairside workflows, these implies that the fabrica0on of the dental restora0ons will be made
during the same appointment in the clinic using digital tools.
(5, 6) The advantages of chairside
workflow that have been described and not limited to real 0me scanning and visualiza0on of
the final impression, easy repeatability, no need for impression trays, no wear of the casts, rapid
communica0on, pa0ent sa0sfac0on, no need for temporary restora0on, cost effec0veness.
(7)
The new possibili0es exponen0ally increased the amount of research and development of new
materials.
(8)
1.2. Restora-ve den-stry
Restora0ve den0stry is the specialty that focuses on the replacing and fixing damaged or
missing teeth. The materials used during this process have been evolving towards tooth colored
materials due to the esthe0c demands of the pa0ents and the constant evolu0on and
improvement of the materials.
(9) This development has focused on the reliability of the
adhesive bonding of the material to the tooth structure, minimal invasive approaches,

2
mechanical proper0es and esthe0c appearance.
(10) Modern den0stry has shihed the
restora0ve approaches to a much more minimal invasive approach to try to preserve dental
structure. The dental structure preserva0on is cri0cal for the longevity of both the teeth and
the final restora0ons.
(11, 12)
In general, depending on the amount of tooth structure that is involved in the defect of the
tooth that needs to be restored, two different approaches can be made to restore the tooth.
The direct method is usually referred to restoring a tooth that has minimal tooth loss and the
main structure of the tooth is preserved. This method is less invasive and it can be performed
in one single appointment.
(13)
The indirect method is usually used in cases in which the tooth structure has been severely
affected by the defect. The approach will be more aggressive as it will need to create a path of
inser0on of the restora0on and removing undercuts. The indirect approach will be more
expensive than the direct one, however, becer anatomy and the material used usually has
becer mechanical proper0es that the direct materials as it will be processed outside of the
pa0ent’s mouth.
(14)
1.3. How the cad / cam process works
CAD/CAM systems consist of three different parts that are involved during different steps of the
process. The first step is the data acquisi0on or scan, the aim of this process is the acquisi0on
of data from the desired prepara0on and other structures to create a virtual impression.
(15) The
second part of the process is the designing of the virtual restora0ons or appliances using a
dedicated sohware that will use the ini0ally created virtual cast. Finally, the manufacturing

3
process that will consist on transforming the virtual design into a real restora0on using different
manufacturing methods such as milling or 3D prin0ng as represented in Figure 1.
(16)
Figure 1: Digital Workflow
1.3.1. Scanning technologies
There are different methods of taking dental impressions, conven0onal methods have been
based on taking a physical impression with a material, such as polyvinylsiloxane, alginate, or
others, that aher a certain seqng 0me will preserve the shape from the pa0ent’s dental arch.

4
This impression is then poured into stone models. The methods of taking the dental
impressions have evolved a lot in the past decades, moving towards a digitaliza0on process
involving intraoral and extraoral scanners based on 3D digital technology that will allow crea0ng
digitalized 3D impressions.
(17) Intraoral scanning has evolved into both intraoral and laboratory
based scanners.
(18)
Intraoral scanners have not only allowed the crea0on of a virtual model but also has allowed
the professionals to have another tool to explain the pa0ent the different treatment op0ons.
Less pa0ent discomfort has been reported, especially in the pa0ents with a gag reflex or even
children.
(19)
On the other side, desktop scanners are available to be used to scan models, with less error
related to the operator and higher precision, reported to be between 8-15 µm and the trueness
between 24-33 µm, having less than 1 µm standard devia0on when we are looking at the most
recent desktop scanners.
(20)
One of the main features that the intraoral scans should have is accuracy, with the capability to
take accurate impressions.
(21) Accuracy is described as both precision and trueness.
(22) While
precision is the closeness of the values of different rests. The trueness on the other hand is the
closeness of the values to the real metrics, also known as the true values.
(22) It is a complex
process comparing the capabili0es of the different scanners in terms of accuracy. The different
scanners consist on different technology and each one will require a specific scanning
technique, which makes it more complex to standardize and compare the different scanners
available.
(23) Accuracy of op0cal impressions has been reported to be as accurate as

5
conven0onal impressions for individual restora0ons and for restora0ons with 4 element bridges
on teeth and implants.
(24)
Other capabili0es that are interes0ng when assessing the different intraoral scanners is the
need for powder to achieve a mac surface to be able to scan. While it was a common
requirement of the intraoral scanners when they were first introduced, the need to apply a
powder on the surface of the teeth, usually a 0tanium dioxide powder, that will eliminate the
reflec0on of natural teeth and create an even surface, adding an average of 13 – 85 µm (25) of
thickness to the original shape.
(26) This powder it’s no longer needed in modern intraoral
scanners, solving the inconvenience for the pa0ent and also, avoiding accumula0on of powder
in different pacerns that will end up affec0ng the surface to be scanned.
(27) This has become a
possibility due to the evolu0on of digital scanning technologies.
(28) It has been seen that the
translucency of the materials that are scanned will also influence the accuracy of scanning,
while the more translucent materials show less accuracy in general.
(29) While different finishes
do affect the accuracy of intraoral scanners, with polished materials such as PMMA or
composite resins usually providing the best results.
(30)
The speed of scanning is of great importance in an op0cal scanner. Although it is true that the
new intraoral scanners have been reported to be faster than the older ones, the experience of
the clinician handling the scanners.
(31)

6
Another concept that plays a big role in dis0nguishing
different intraoral scanners is the size of the 0p. Smaller
0ps are more convenient to be capable of reaching the
most posterior areas of the dental arch avoiding
discomfort to the pa0ents (Figure 2).
(32, 33)
When looking at the digital workflow, we can dis0nguish
between open-source or closed systems. While the
closed sohware will only export in the proprietary file,
which will only be possible to use with the same
manufacturing company or system from the scanner.
Open source systems will export in open-format files
such as STL, OBJ, PLY and others that can easily be used with all CAD prosthe0c systems.
(23)
There’s a range of different technologies that are available in the market. The device is
composed of a digital camera, computer, and a sohware. The scanner will record and convert
the images into a 3D digital model.
(34) Some of the technologies available are the following:
- Triangula0on: By applying a calcula0on of distance to a single point from two different
points, it can calculate the posi0on of the reference in the image. Scanners such as
Medit I700 (Seoul, South Korea) use this technology.
- Confocal: This technology is based on the focused and defocused images at different
depths. As the camera moves around and acquires different perspec0ves of the object,
Figure 2: Intraoral scanner 8p

7
the sohware will be able to reconstruct the model (34), scanners like Trios 3 ( 3Shape,
Copenhagen, Denmark), iTero Element 2 ( Align technology, Tempe, AZ US)
- Ac0ve wavefront sampling: An off axis aperture module will be going around the camera
and will create a rota0on of the poi and the informa0on captured by the camera will be
recorded with the sohware.
(35)
- Stereophotogrammetry: The 3D model is calculated through algorithmic calcula0ons
from different images. This will relies on passive light projec0on and it’s a cheap
technology to produce.
(36)
Common errors during the intraoral digital scanning are the accumula0on of errors during the
s0tching process in cases where there’s a lack of references or anatomic structures.
(37)
Scanners that are based on con0nuous imaging like Medit I700 have been reported to have
becer performance compared to image based scanners.
(38)
1.3.2. Sohware & design
Once the digitaliza0on of the case been achieved with the scanner, the next step is the use of
the design sohware to create de virtual restora0ons designs. These sohware will allow the
clinicians and the dental technicians to design anything from wax-ups, anatomical crowns,
inlays, par0al crowns, fixed par0al dentures and many other prosthe0c restora0ons.
(39)

8
1.3.3. Manufacturing methods
It was not un0l few years ago that CAD / CAM technology in den0stry was very much related to
only one method of manufacturing which was the subtrac0ve manufacturing, based upon a
block of a material that was reduced using computer aided technology to achieve the digitalized
model aher milling, grinding, drilling, turning, and polishing. It is known that this process can
lead up to 90% of waste material, in addi0on to other drawbacks such as the crea0on of
microcracks on the surface of the materials.
(40, 41)
Newer approaches to produce the final restora0ons and to manufacture the designs has been
focused on 3D prin0ng, also known as addi0ve manufacturing. This process is based on
building up a shape layer by layer, first introduced in the dental sector in the 1980(41).
1.3.3.1. Subtrac0ve manufacturing
Subtrac0ve manufacturing is based on shaping a preformed block into a desired shape. This
method has shown to be very reliable but, on the counter side, it has been described to
produce a lot of waste product during the process.
(42) Milling machines can be dis0nguished on
the number of milling axes that they have; 3-axis devices, 4-axis devices, and 5-axis devices.
(43)
3-axis milling devices are the more simple milling machines, allowing for short milling 0mes but
less capability to mill complex shapes with undercuts, 4-axis milling will allow for more complex
shape milling and the capability to save more material and milling 0me, finally the 5-axes milling
machines that allow to mill more complex geometries.
(44)
Milling can also be classified between dry processing and wet milling. Dry milling will usually be
used for green stage zirconia stages, which makes the milling device more affordable, and the

9
material will not absorb water during the process. Wet milling is used mostly using carbide and
diamond burs, the water will protect the bur and the material from overhea0ng during the
milling process, the sintered materials will have less distor0on if milled in that stage.
(44)
The use of the different burs and the number of uses will have an influence on the surface finish
of the restora0ons depending on the materials used. With diamond burs it has been reported
a becer margin and surface finish with new burs, only materials like dental composites will be
less affected by the repeated use of the burs.
(45)
1.3.3.2. Addi0ve manufacturing
Addi0ve manufacturing, also known as 3D prin0ng, has several advantages over milling or
conven0onal manufacturing techniques. Those include the reduced number of resources to
produce, less human interven0on and less material waste and energy needed for produc0on,
which in the end translates to less environmental impact.
(46) This technology has a growing
interest in the dental and medical fields due to the wide range of capabili0es that it offers. In
the case of den0stry, some of the applica0ons that have been described are surgical guides,
temporary restora0ons, bite-guards, orthodon0c appliances, scaffolds and other.
(47)
There are many available different technologies for addi0ve manufacturing, including the
stereolithography (SLA), selec0ve laser sintering (SLS), fused deposi0on modeling (FDM), Direct
metal laser sintering (DMLS), polyjet 3D prin0ng (PJP), Inkjet 3D prin0ng (IJP), laminated object
manufacturing (LOM), color-jet-prin0ng (CJP), electron beam mel0ng (EBM).
(48) Different
prin0ng technologies are used depending on the materials that are used, addi0ve
manufacturing allows the use of materials such as composites, metals and ceramics adding
layer by layer one on top of the other one following the digital designs.
(49) The most wide

10
spread 3D prin0ng technology in den0stry are both the Stereolithography (SLA), and the Digital
Light Projec0on (DLP) due to the cost, ease to use and applica0ons. (50)
Recent studies have shown higher accuracy of addi0ve manufacturing techniques compared to
the subtrac0ve. (51) specially in high quan0ty produc0on.
(50) When restora0ons created both by
subtrac0ve and addi0ve manufacturing, it has been seen that the addi0ve manufacturing can
achieve becer accuracy compared to the subtrac0ve ones.
(51) While accuracy is a very
important aspect in the manufacturing of dental restora0ons, it is also important the efficiency
of the process and the cost. It has been seen that the subtrac0ve methods can be more 0me
efficient than the subtrac0ve ones. 3D printed composites need far less investment, around
$1600 for a new printer, a used milling machine may range around $14,000.
(50)
Many different aspects can influence the result aher 3D prin0ng. One of the important aspects
to take into considera0on while 3D prin0ng is the thickness of the layers. Thinner thickness will
represent more accuracy and more produc0on 0me, it has been assessed the op0mum
thickness layer to achieve increased hardness of the material at 50µm.
(52)
1.4. Materials
New materials have been developed to be produced using digital manufacturing technologies,
including subtrac0ve methods and addi0ve ones. The broad amount of materials include glass
ceramics, zirconia and dental composites.
(53)
1.4.1. Metals
Metals such as 0tanium, 0tanium alloys and chrome cobalt alloys can be processed using
milling devices.
(44) These materials have also been adapted to be processed using addi0ve

11
manufacturing processes and taking advantage of the technology.
(54) Different addi0ve
manufacturing methods have been used to process metals, like Selec0ve laser sintering or
powder binders technology. (55)
1.4.2. Ceramics
There are also many different types of ceramics available to be milled using digital subtrac0ve
manufacturing. In general the ceramics can be classified as following (47) (Figure 3):
1- Silicate ceramics: including feldespathic ceramics, leucite-reinforced ceramics, and
lithium disilicate ceramics.
These materials contain a glass matrix which makes them highly esthe0c materials. These are
bricle materials that have a low fracture resistance. Feldspathic porcelain were the first millable
blocks.
(56) Leucite reinforced ceramics where then introduced to improve the mechanical
proper0es from feldspathic ceramics showing good clinical success when used in areas with
not much mechanical load.
(47) Lithium disilicate blocks are a ceramic glass with a crystalline
phase that is based on lithium disilicate and lithium orthophosphate crystals. This ceramic is
capable to withstand occlusal forces even in high demanding areas like posterior teeth.
(57)
2- Oxide ceramics or polycrystalline ceramics: including aluminum oxide ceramics and
zirconium oxide ceramics.
The zirconium oxide ceramics can be further classified as 3 mol % ycria-tetragonal zirconia
polycrystals (3Y-TZP), 4 mol % ycria-par0ally stabilized zirconia (4Y-PSZ) and 5 mol % ycriapar0ally stabilized zirconia (5Y-PSZ). This ceramics have high mechanical proper0es with flexural

12
strengths of up to 1200 MPa, also with the capability to prevent the propaga0on of cracks in
the material thanks to the transforma0on toughening that is characteris0c of the zirconia.
(58)
3- Infiltrated ceramics / resins.
In this group two different materials can be found. On the one hand, the polymer matrix
infiltrated with ceramic filler par0cles, and the blocks that consist of a ceramic network that is
further infiltrated with a polymer like Vita Enamic (Vita, Richmond, VA). These materials have
shown high load capabili0es, resistance to fa0gue, high modulus of elas0city and no need to
sinter or crystalliza0on, which simplifies the manufacturing process.
(59, 60)
Although Lava Ul0mate has been classified as a ceramic, this is a material that it is based on a
nanofiller composite based on the Filtek Supreme Ultra (3M ESPE) with colloidal silica and
zirconium oxide spherical par0cles in an agglomerated, roughly a micron, and
nonagglomerated form (80%wt and 65%vol) embedded in a dimethacrylate resin (TEGDMA,
bisGMA, bisEMA, UDMA).
(61, 62) It has an ini0al high strength that, thanks to the rela0ve
elas0city of the polymer in which the fillers are embedded in, allows to avoid crack propaga0on
that may happen during fa0gue tes0ng. This material has a low modulus of elas0city (17.25
Gpa (63)) that has shown signs of fa0gue of the material aher mechanical tes0ng.
(62) The
hardness of this material (121.70VHN (63)) is lower than the hardness of enamel. These
composite materials have increased amounts of fillers, even higher than a desired threshold,
making the wear abrasion transi0on from fa0gue to abrasive wear, increasing the amount of
volumetric loss.
(64)

13
Figure 3: Classifica8on of dental ceramics
1.4.2.1. 3D prin0ng ceramics
Ceramics is one of the fields of interest for 3D prin0ng, Experimental prin0ng has been capable
to print glass ceramics with considered excellent mechanical proper0es by using lithographybased technology and Stereolithography 3D prin0ng.
(65) Oxide ceramics on the other hand
have also been studied for addi0ve manufacturing. It has shown that using this methods can
reduce the 0me of fabrica0on and improve the treatment efficiency, however, high internal
stress and cracks are some of the downsides from this method of manufacturing the zirconia
with 3D prin0ng.
(66)
3D prin0ng of zirconia is based on prin0ng a suspension based on the ceramic and
photopolymer mixture that will be used as a binder. Then the binder needs to be removed using
a thermal postprocessing, and the final green stage material will be fully sintered.
(67)

14
Now, the manufacturing of ceramics is s0ll a complex process using addi0ve manufacturing, as
the mechanical proper0es achieved with the subtrac0ve methods cannot be reached with the
addi0ve processing of dental ceramics.
(46)
1.4.3. Polymers
Polymers are high-molecular-weight chemical substances that are based on repeated units
(monomers), as the units add up to each other, the material proper0es will change. The
characteris0cs of this materials is polymeriza0on, which will form the high molecular weight
compounds. A monomer will become a polymer. There are two different types of polymers, the
linear branched and the cross-linked polymers.
(68)
There is a wide range of polymers available in den0stry and a broad applicability of those. From
materials to be used for dental impression and bite registra0on like polyvinylsiloxanes,
polyether, polysulfides, condensing silicones and others.
(68) To polymers with restora0ve
applica0ons like:
1.4.3.1. Types of polymers
1.4.3.1.1. Acrylic Resins
This resins are derivates of the ethylene and contain vinyl group on the func0on.
(69) Poly (methyl
methacrylate), acetal and polyamide can be milled out of blocks. Usually, the material will be
used for long-term single crowns or even fixed par0al dentures. Thanks to the enhanced
physical proper0es and the ease to polish the final restora0on, highly esthe0c restora0ons can
be made out of this material.
(70)

15
PMMA is a well-known material that was first introduced in the 1930s.
(71) Due to the lower cost,
ease of manufacturing combined with good stability of the material when exposed to the oral
environment, this has become one of the most popular polymers in den0stry. This material can
be addi0vely manufactured using fused deposi0on modeling.
(72) This material, however has
shown a downgrade in the mechanical proper0es when it is 3D printed and compared to
conven0onal methods of manufacturing.
(73)
1.4.3.1.2. PEEK
Reinforced (high-performance) polymers such as the polyetheretherketone (PEEK) have good
mechanical proper0es as well as physical and biological characteris0cs. These materials are
easier to manufacture than metals. This material has shown becer results in two surface wear
tests compared to composite and PMMA.
(74)
1.4.3.1.3. Composite resins
The composi0on of the dental composites is based on an organic matrix; most of the
composites use bis-GMA, which has a high viscosity, combined with other dimethacrylate like
diethylene glycol dimethacrylate (TEGDMA) or urethane dimethacrylate (UDMA) within
others.
(75) These monomers will polymerize following an addi0on polymeriza0on mechanism,
which is known as a chain-growth polymeriza0on that needs to be ini0ated by free radicals.
New development is focused on new formula0ons with reduced polymeriza0on shrinkage and
self-adhesive proper0es. These new monomers such as siloranes have shown good mechanical
proper0es with reduced shrinkage rates.
(76) Other formula0ons include high molecular weight
urethane with a rigid central sec0on and flexible end groups, dimethacrylate with bulky space-

16
filling central groups or high molecular weight phase-separa0ng dicarbamate with hydrophobic
side chains.
(69)
3D printed resins are based on polymer monomers, combined with photo ini0ators,
prepolymer and diluents.
(77) Usually, the polymeriza0on of the resin will happen in ranges
between 250-300 nm wavelength, star0ng a crosslinking process between the monomers. This
materials are usually used with digital light processing 3D printers & Stereolithography 3D
printers.
(78) The applica0on of the materials is for crows, bridges, surgical guides, models, and
other prostheses.
1.4.3.1.4. Other polymers
Polymers are the most common material used for dental and surgical appliances, ranging from
custom surgical guides, custom trays, dental casts, temporary restora0ons, crowns, bridges and
others.
(79) The materials that can be found in this realm are Polycaprolactone (PCL), Polylac0c
acid (PLA), Poly (lac0c-co-glycolic acid) (PLGA) and the ultra violet (UV resins).
(80)
Polycaprolactone
PCL is widely used in 0ssue engineering due to the superior biocompa0bility characteris0cs,
adjustable degradability, and wide applica0ons in the biomedical fields. It is a material that is
easy to use with fused deposi0on modeling manufacturing due to the low mel0ng point.
(81)
Polylac=c acid
PLA is a biodegradable and environmentally friendly polymer. This material can be
manufactured using the fused deposi0on modeling. The applica0ons of the material range from
guiding bone regenera0on and 0ssue regenera0on.
(82)

17
Poly (lac=c-co-glycolic acid)
PLGA, is a copolymer of PLA and PGA, with high biocompa0bility and biodegradability, allowing
for cell prolifera0on and an0microbial proper0es.
(83) This material will be processed using fused
deposi0on modeling.
(80)
1.4.3.2. Ini0ators - Polymeriza0on
Monomers need to be joined together through either a condensa0on or addi0on reac0on. In
general terms, the addi0on polymeriza0on consists of monomers that are ac0vated on at a
0me and joining one by one, while in the condensa0on polymeriza0on, all the molecules
ac0vate at the same 0me. The stages in the polymeriza0on process are the induc0on,
propaga0on, chain transfer and finally the termina0on.
(69)
These radicals can be created either by a chemical acBvaBon or thanks to an external energy
ac0va0on, usually light or heat.
(69)
Self-curing composites, or chemical ac0vated composites contain benzoyl peroxide as an
ini0ator and an aroma0c ter0ary amine as a co-ac0vator. The combina0on of this two will
ac0vate the benzoyl and will form free radicals.
(69)
On the other hand, light ac0vated composites have photo ini0ators that can be classified into
two different groups: photo ini0ators type I and photoini0a0ons type II. What is special about
this molecules is that they will be capable of absorbing irradia0on and use the energy to create
free radicals.(84)
Type I photo ini0ators, like lucerin TPO or other derivates such as Ivocerin, will require less
photons to start the process compared to the type II such as camphorquinone and phenyl

18
propandione, as the last ones s0ll require energy from another agent such as an amine.(85)
like camphoquinone which will be accelerated by a ter0ary amine.(86, 87)
Another important aspect to take into considera0on is the range of light wavelength
absorbance of such molecules so that they can ini0ate the polymeriza0on process.
Camphorquinone is most sensi0ve in lights that are in the range of blue wavelengths (360 to
510 nm) and a the highest absorbance at 468 nm.
(88) Type I photo ini0ators are more sensi0ve
to wavelengths in the range between the blue and the violet range (390-410nm). In the case of
the Icoverin, it is highly sensi0ve between 400 and 430nm (Figure 4Error! Reference source
not found.)
(84), and for Diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide, also known as TPO,
the absorbance range is between 380 – 425 nm, with a peak absorbance at 400 nm. (89)
Figure 4: Classifica8on of photo ini8ators

19
Milled composites show higher degree of conversion than direct composites, this is due to the
possibility to manufacture in high pressure and high temperatures, which will lead to higher
mechanical proper0es and wear resistance.
(90) Also, composites with light ac0vators like TPO
have shown increased hardness values. (89, 91)
1.4.3.3. Fillers
Dental composites are incorporated in the organic matrix between 30% - 70% by volume. This
will allow the final composite to have becer resistance to mechanical, physical and chemical
aggressions from the oral environment.
(69)
The fillers will provide the composite with reduc0on of the polymeriza0on shrinkage, less
thermal expansion and contrac0on, decreased water sorp0on, reinforcement, more viscosity
and help with control of workability and impair radiopacity.
(69) Most common dental fillers were
ini0ally quartz, this material was complex to polish and was very abrasive to antagonists, thus
the similar material but not as hard, the silica was introduced as a filler. Other materials used
as filler par0cles have been fused quartz, aluminum silicate, lithium aluminum silicate,
ycerbium fluoride, barium, stron0um, zirconium and zinc glasses.
(69)
Dental composites are presented in different consistencies, from flowable composites which
can be dispensed through a syringe all the way to packable composites with higher resistance
to packing instruments. Flowable composites are usually achieved by reducing the amount of
fillers and adding other modifiers such as surfactants that will help achieve a higher flowability

20
of the material and avoiding the removal of big amounts of fillers and affec0ng its mechanical
proper0es.
(92)
As a composite, the 3D printed composites have shown that the addi0on of zirconium oxide
nanopar0cles significantly improved the mechanical and physical proper0es of the resins
compared to the ones with no fillers. The higher the filler content, the higher the hardness of
the 3D printed composite.
(93)

Classifica0on of dental composites depending on fillers size
Dental composites are mainly dis0nguished depending on the characteris0cs of the reinforcing
fillers, regarding size, material, and load. While ini0ally dental composites were filled with big
par0cle sized fillers with an average size that would exceed 1 µm and even up to 50 µm. These
would be very strong but would be almost impossible to polish. The industry started reducing
the filler sizes to solve the problems regarding polystability and esthe0cs reaching par0cle sizes
ranging from 5 nm and 100 nm.
(94)
This is the reason why there is a contemporary classifica0on of the dental composites based on
the size of the fillers as shown in Table 1 (95):

21
Table 1 Classifica8on of resin based dental composites (95)
Class of composite Par0cle size and filler
characteris0cs
Recommended use of the
composite
Microfilled composites
40 – 1,200 nm
30% - 60% Volume
Adequate esthe0cs
Reduced mechanical
proper0es
Hybrid composites
60 – 1,000 nm
60% - 70% Volume
Good mechanical
proper0es
Hybrids >600 nm, Irregular shapes Complex polishability
Microhybrids
400 to 1,000 nm. (average 400-
600 nm)
Includes rounded par0cles.
60% volume
Becer polishing, universal
composites
Nanohybrids
10 to 2,000 nm (average 200 –
300 nm).
70% Volume
Like micro hybrids
Nanofilled
100 nm or below
55% - 70% Volume
Like micro hybrids but high
polishability and gloss
reten0on.
1.4.3.4. Coupling agents
It is important that the resin matrix bonds to the filler par0cles, allowing becer distribu0on of
mechanical forces. The coupling agent will be a difunc0onal surface-ac0ve compound that will
adhere to the surface of the filler par0cles and that will react as well with the monomers. The
most common coupling agents are the oligosilanes. The γ-methacryloxypropyl trimethoxysilane
is the most used one as it will create siloxane bonds to the surface of the fillers and covalent
bonds with the resin.
(69) The silanes will be used in the cases in which the composites fillers are
based in silica-based materials like quartz, silicon dioxide, silicate glasses.
(96) Other used

22
coupling agents are the organo0tanates and the organozirconates, however this last ones are
less used due to the higher cost of manufacturing.
(97) In the case of zirconia, phosphates such
as 10-methacryloyloxydecil dihydrogen phosphate (MDP) have been inves0gated to achieve
becer bonds with the material by crea0ng a chemical bond with the zirconia while the Zr-O
and P-O bonds turn into Zr-O-P interac0ons.
(98, 99)
The use of coupling agents has demonstrated that it makes the material more hydroly0cally
stable, as the interface between the fillers and the matrix will become more stable and thus
the materials will be more resistant to humid condi0ons.
(100)
1.4.3.5. Manufacturing methods for indirect polymer restora0ons
Since the beginning of 3D prin0ng in the 1970s, there has been a lot of development in the
technology and the different materials available for manufacturing using this technology. The
amount of possibili0es and materials also depend on the field that they are used for; in the
case of den0stry, the most common materials available for 3D prin0ng are polymers, ceramics
and metals due to the high accuracy and high biocompa0bility that they achieve.
(80) More
recently, 4D prin0ng has also been disrup0ng in the industry as it allows to use different
materials with different proper0es in one single print.
(101) Composites methods of
manufacturing
Composites are resins that are composed of an organic resin matrix which has embedded
inorganic or organic fillers together with other components such as ini0ators, stabilizers, and
pigments. This material is usually applied, modeled polymerized and finally polished intraorally,
however, pre-polymerized ready to mill blocks of the material are also available.
(47) When

23
compared to other materials such as Emax CAD, which have higher hardness than enamel, they
will have least wear effect of the antagonist.
(102) The ease to process the material, with easy
processing material, polishing and adding staining are some of the interes0ng aspects of the
material.
(47) The newer dental composites available to be manufactured using an addi0ve
process have shown to have similar marginal adapta0on when compared to milled composites,
thus, the improvement of the mechanical proper0es of these would open a big scope of
interest in restora0ve den0stry for the materials.
(50)
There is certain amount of research and reviews about composite 3D printable materials for
provisionaliza0on and it those have shown that compared to conven0onal CAD / CAM milled
provisionals, the printed Provisionals have shown superior mechanical proper0es in terms of
fracture strength, flexural strength, elas0c modulus, peak stress, and wear resistance. However,
toughness, resilience, microhardness appears to be becer for the milled materials, similar as
the water sorp0on, solubility, and color stability.
(103)
New composite materials for 3D prin0ng are being introduced to the market branded as for
defini0ve / permanent restora0on materials. VarseoSmile Crown Plus is a composite based on
silanized dental glass with 0.7µm embedded at a 30-50% weight in a resin matrix based on 4-
0- isopropylidiphenol, ethoxylated and 2-methylprop-2enoic acid. The cured composite has a
modulus of elas0city of 6.79 Gpa and a report hardness of 45.78 VHN.
(63) There are reviews of
the use of different materials in certain situa0ons such as for inlays. A comparison between
ceramic inlays and composite -based inlays demonstrated that ceramic inlays perform becer in
the short term, with the most common causes of failure being fracture of the restora0on and

24
caries.
(104) Also, the composite materials have been reported to be more vulnerable to wear
when compared to the ceramics.
(102)
In 3D prin0ng, the viscosity of the resin has a big influence on the overall result, while low
viscosity resins are becer for speed and curing rate. However on the counter side, the low
viscosity makes the fillers of the resin sediment and create a non-homogeneous prin0ng
pacern.
(105)
Nowadays, the classifica0on of dental polymers does not have a clear line with dental ceramics,
as the new materials try to achieve blends of the two of these to achieve mechanical proper0es
in between the two different materials. A scheme with the different groups of materials
considered tooth colored is proposed in Figure 5.

25
Figure 5: Classifica8on of tooth colored dental materials

26
1.5. Mechanical proper-es of the materials
The study of the mechanical proper0es of the materials is of great importance as we will be
able to understand more the behavior of the material in func0on and in the oral environment.
Many of the failures of dental materials is due to the fracture of the material.
(106)
The most common proper0es of the materials measured are the strength, toughness, fracture
toughness, elas0c modulus, indenta0on hardness and wear.
1.5.1. Strength
Strength is also known as the resistance to catastrophic failure. This is not an inherent property
of the material but more dependent on the design of the restora0on / samples. Flexure of the
material, typically by applying 3 point bending (107), or other similar methods, it will help
measuring the strength of the material. Biaxial flexure (108), tension (109) and compression,
impact and compression tests have also been used to analyze this characteris0c of the
materials. (110)
1.5.2. Toughness
Fracture toughness is an inherent property of the material, and it should be independent to
the shape used for tes0ng. Usually, the tests are based on pre-cracking the surface of the
material before applying a load to fracture it. Different methods have been described to test
the toughness of a material, from compact tension, double torsion, single edge notch and
others.
(110)

27
1.5.3. Edge Strength / Chipping
Although there is no standard method for this test, this is a relevant test for materials that will
break in the corners if slightly unsupported. Usually the distance to the edge chosen is 0.5 mm
as this will have an influence in the final result. (111)
1.5.4. Fa0gue resistance
This is a very important property from the materials that are under loads for long 0me periods
of 0me. This con0nuous loading will make the material accumulate damage over the 0me,
which can lead to the failure of the material.
(110) Some examples are the fa0gue resistance of
certain materials over den0n or enamel. It has been assessed the fa0gue resistance of glass
ceramics and dental composites over both of this substrates, a value of 900 N over enamel and
805 N over den0n for a lithium disilicate and for composite being 815 N and 1080 N over den0n
respec0vely. (112)
1.5.5. Elas0c modulus
It is the capability of a material resistance to being deformed in an elas0c way. Tensile tests as
well as flexural bending of the material will be the methods to address the elas0c modulus of
the materials.
(110) Examples for elas0c modulus are 13.63 Gpa for Lava Ul0mate, 31.43 Gpa for
Enamic, a polymer infiltrated glass ceramic. (113)
1.5.6. Wear
Wear can be described as “the ul0mate consequence of interac0on between two different
materials or surfaces, which will result in a gradual removal of material”.
(114)

28
1.5.6.1. Types of wear and classifica0on
In general concepts, tribology classifies the main methods of wear in abrasion, adhesion,
fa0gue and finally 0bochemical wear, considered a chemical dissolu0on during wear. (115)
-Abrasive wear is the most common type of wear. It happens when a harder material with
asperi0es contacts with a soher material. Depending if the asperi0es are part of one of the two
materials or is found in between the two material as a loose phase, the former will be classified
into two body type of wear, whereas the later will be classified as three body type of wear. (114)
The different abrasive wear representa0ons can be seen in Figure 6:
Figure 6: Abrasive wear classifica8on
-Adhesive wear happens when the two materials become cold welded when two materials are
slicing one against the other. There will be a transfer of material from one of the surfaces to the
other one (Figure 7).
(114)

29
-Fa0gue wear happens when the area in front of the compressed zone of the mo0on, a plas0c
deforma0on will happen and create tension behind the zone of pressure. This will nucleate
fractures under the surface which will eventually propagate towards the surface and the
material that gets surrounded by the crack will be lost (114) as seen in Figure 8.
Figure 8: Fa8gue wear
-Tibochemical wear, also known as chemical wear or corrosive wear happens when there is a
chemical reac0on on the surface of the material, which can be easily removed aherwards with
contact with another surface (116) as seen in Figure 9.
Figure 7: Adhesive wear

30
Figure 9: Corrosive wear
In den0stry however, the concept of wear is considered as the loss of tooth structure. This wear
in den0stry is further classified into acri0on (when there is abrasion in the contact areas
between two teeth), abrasion (when the wear happens in the areas where there is no direct
contact between two dental surfaces) , erosion (when the loss of dental structure is acributed
to the chemical effects) and finally abfrac0on (in the cervical parts of the tooth due to
mechanical behavior of the dental structure). (117)
1.5.6.2. Clinical wear & natural den00on
Natural den00on also undergoes a wear process throughout the years, the mean annual
physiological ver0cal loss for enamel on human den00on has been reported to be within the
range of 20µm to 30µm in posterior teeth. (118)
In the natural den00on, when teeth get in contact with no food or any intermediary, a twobody wear will happen between the two contac0ng surfaces. (114) Usually, during mas0ca0on
teeth will be sliding distances form 0.9 to 1.2mm and the forces will range between 3 to 36 N.
(119) This forces have been reported to ho up to 150-800N in certain cases. (120) There are

31
pathologies like bruxism that will increase the amount of direct contact between teeth and
forces, resul0ng in increased amounts of wear of the tooth structure. The prevalence of this
condi0on has been reported to be between 8% to 31.4%. (121)
However, nowadays most of our pa0ents will have different materials in the mouth, leading to
interac0on of different materials with each other, thus it is important to understand the
behavior of such materials to be capable of choosing the materials that becer behave in those
condi0ons.
-Ceramic - Enamel interac0on
It has been studied the effect of ceramics when in contact with the natural den00on. In general
terms, it has been seen that the higher strength ceramics like zirconia do not create as much
erosion as low toughness ceramics. This can be explained as the higher toughness materials
like the zirconia will behave as a two body and three body abrasion, highly dependent on the
final polishing of the surface of the material. On the other hand, the low toughness ceramics
will end up crea0ng micro-cracks and abrasion of the ceramic that will increase the two body
and three body abrasion of the surface, increasing aher some 0me the dental wear. (122)
-Resin based materials– Enamel interac0on
Wear of composite materials show a specific pacern that is related to the composi0on of such,
which consists of filler par0cles embedded in a bricle polymer. (123)
The characteris0cs of wear of composite is in accordance with its composi0on. The wear
resistance of these materials will depend on how the forces can be transferred in the material.

32
Ideally the forces would be transferred from the matrix to the filler par0cles, shape, size and
hardness of these fillers will have a direct influence on the mechanical proper0es of the
material, as well as the bonds within the matrix and polymeriza0on, and the bond between the
matrix and the filler par0cles. (124)
Wear will produce par0cles that may be released and therefore swallowed, having poten0al
toxic or biological hazard effects. In the case of composites, it is the release or leaching of
monomers and co-monomers and filler par0cles. This can lead to accumula0on of such
materials in the 0ssues which can cause diseases to the kidney, liver, lungs, and intes0nes. (123)
Filler size will have an important effect on wear. The resistance of the material will depend on
the size of the fillers compared to the deforma0on created by antagonis0c material. If the
deforma0on of the surface is bigger than the filler par0cles that the material contains as fillers,
this means that the material will behave as one with consequently similar wear rate of the resin
as the par0cles will have not much influence as the actual forces will be distributed along the
resin. If the deforma0on is then smaller than the filler par0cles, the par0cles will behave
differently than the resin matrix and the wear will be decreased as the par0cles will be taking
the forces of the antagonis0c material (114). However, there might be phase separa0on and sub
surface damage can occur. (114)
A deforma0on of the polymer may happen in a plas0c manner in the case of abrasion, or it can
be elas0c, which will lead to subsurface fa0gue of the material. The difference between the
two processes may not be as clear. (114)

33
1.5.6.3. Clinical research of wear
The wear evalua0on in clinical research is based in two different models. The first one is based
on clinical categoriza0on depending on the clinical aspect of the teeth. The second method is
by using replica models by taking intraoral records. (114) Intraoral digital scanners have been
used as a method to acquire the data. These scanners may not be as user friendly when it
comes to wear analysis as they have been created for other purposes such as CAD / CAM
den0stry. However, some of the intraoral scanners have already shown enough accuracy to be
used in the evalua0on of wear and it can be comparable to the replica models made with
polyvinylsiloxane impressions. (118)
1.5.6.4. In vitro research of wear
The understanding of dental wear and how the materials behave in such condi0ons is important
to develop new materials and to make sure that the materials will behave accordingly in a
uniform manner compared to the natural den00on; with similar corrosion, mechanical,
tribological behavior, cost, biocompa0bility and aesthe0cs. (125) Clinical studies can be complex
and 0me consuming, involving ethical issues. This is one of the reasons why in lab simula0ons
are popular to evaluate wear on the materials. Most of the studies are based on water-saliva
lubrica0on tes0ng for two-body wear, which would be known as acri0on when using the dental
nomenclature. (122)
Different methods have been used to analyze the surface of the evaluated materials aher the
wear has been performed over the final materials and over replicas created with
polyvinylsiloxane impressions and poured with plaster aher. From using laser scans, 3D op0cal
scanners, both desktop and intraoral scanners and profilometry methods.
(126, 127)

34
1.5.6.5. Wear simulators
Different wear simulators and methods have been described and used in research of dental
materials wear tes0ng. Some of the most common methods are the following ones:
-ACTA-method: Developed in the Dental Collage in Amsterdam. This method is based on two
metal wheels that rotate in different direc0ons. The material and antagonists are mounted on
the wheels and a force of 15N is used. A slurry of white millet seeds is used. A profilometer is
used to measure the maximum ver0cal loss aher 50,000, 100,000 and 200,000 cycles. (128)
-Alabama-Method: Developed in the University of Alabama. Although this method has been
modified mul0ple 0mes, ini0ally a 2mm radius stainless steel stylus hit the sample with no
rota0on, later a rota0on was included and it went from 55N to 75N. (129, 130)
-Ivoclar-method: 8 samples are mounted in the Willitec (SD Mechatronik, Germany), with
antagonists made of IPS Empress ceramic (Ivoclar Vivadent). Glazed twice at 870 ºC. The
antagonist used is of 2.4mm at a height of 600µm. 5Kg are put on the ver0cal bars. Sliding
movements of 0.7mm and the cycles have a frequency of 1.6Hz. 120.000 total cycles are made
with thermos cycling. Both volumetric loss and ver0cal loss can be addressed. (130, 131)
-Munich-Method: Developed at the Maximilian University in Munich. The samples are mounted
on a slicing wear tester. A pin on block design is made, with constant contact with the spherical
antagonist of aluminum oxide of 5mm diameter with 8mm distance and 50N. Bi direc0onal
mo0on. (132)

35
-OHSU-Method: Developed by the Oral Health and Science University in Portland. In this case
the antagonists are enamel cusps, which are in contact with the samples with a slurry in
between made of poppy seeds and PMMA. The cusps are made of human enamel with a
diameter of 10mm and then polished down to 1000 grit silicon. Ini0ally, a pressure of 50N is
used for lineal movement of 8mm. In the end of the path, the load is increased to 80N. A total
of 100.000 cycles at 1Hz with unidirec0onal movements are done. (133)
-Zurich-Method: Ini0ally developed in the university of Zurich, 49N of weight are used in a
frequency of 1.7Hz. Palatal cusps are used mounted at 45º. The samples are mounted in water
together with thermos cycling. Aher 120,000, 240,000, 640,000, and 1,200,000 cycles, the
samples are subjected to toothbrushing with a slurry with toothpaste for 30 min, 30 min, 100
min, and 140 min.
(130)
One of the becer performing wear simulators is the Willytec (SD Mechatronik, Germany)
because of its efficiency and cost. Systema0c evalua0on of the simulator has shown reliable
results and easy modifica0on of test parameters. The simulator is based on dead weights that
are placed on top of the bars that an engine will lower towards the samples. The speed of the
ver0cal and horizontal motors can be easily modified. 2, 4 and 8 samples can be test
simultaneously with or without thermocycling and simultaneous flooding. (110)
The use of a sliding stylus is key in the wear simula0on. It will allow us to create micro fa0gue
to the material. (134) Importantly is also the loading force, as higher loads will usually create
higher amount of wear. (135) In terms of the shape of the antagonist, the sharper the antagonist,
the higher the amount of wear. (132) As for the antagonist material, enamel should ini0ally be

36
the material of choice because of its relevance. The difficulty to standardize such material for
in-vitro use has shihed the material of choice towards other more accessible and more
predictable materials. An alterna0ve material to enamel is the pressed leucite reinforced
ceramic IPS Empress, this material has shown similar wear rates when compared to the natural
enamel. (136)
Other important aspects are the number of cycles that are used during the test. An increased
number of cycles will translate into more wear. Normal pacerns of wear show a much faster
wear at the ini0al phases of the tes0ng and a decrease of wear as the cycles increase. (110)
1.5.6.6. Correla0on in vitro – clinical
Different studies have tried to correlate the in vitro data with clinical performance of the
materials. Moderate correla0on has been seen with the OSHU method, weak correla0on
between the Alabama, Ivoclar, Munich and Zurich methods and no correla0on with the ACTA
method. (130) Ivoclar method however has shown the least coefficient of varia0on together with
the ACTA method. Variables related to volumetric and ver0cal loss have been shown to
correlate when using an IVOCLAR method, while abrasion and acri0on have been shown to be
becer simulated with the OSHU method. (126)
The lack of correla0on that has been described between clinical and in vitro research regarding
the wear should not discourage the use of the in vitro methods, as they help understand the
mechanisms of such wear rather than predic0ng the clinical performance of the materials in
clinical situa0ons. (114)

37
3D prin0ng in den0stry and the available materials have grown exponen0ally. New materials
that have been introduced to the dental prac0ce and, more recently new materials that the
industry state as “3D manufactured materials for defini0ve restora0ons” have been launched
to the market. Not much research has been made about the mechanical and physical proper0es
of these materials, thus, the aim of this research project is to evaluate the wear proper0es of
the materials to further understand the behavior of these materials and compare it to the
available materials for similar applica0ons.

38
1.6.Objec-ve
New materials for CAD/CAM addi0ve manufacturing defini0ve restora0ons are being released
to the market. Few studies have evaluated the mechanical proper0es and how these materials
behave in comparison to the well-established glass ceramics, zirconia, and milled composites.
Therefore, we are targe0ng wear analysis of two different defini0ve composite-based materials
for addi0ve prin0ng.
1.7. Aim
The purpose of this study is to address the wear resistance of 2 different defini0ve composite
materials for addi0ve manufacturing as well as a composite for defini0ve restora0on for
subtrac0ve manufacturing.
1.8.Null hypothesis
- 3D printed composite resin-based defini0ve materials have a similar wear resistance
compared to a composite resin-based milled material.
- The number of cycles does not affect the amount of wear of the materials.

39
Chapter 2: Materials and methods
2.1. Study design
A total of 24 samples were fabricated with 8 samples per group for 3 different materials. The
control group consisted of a subtrac0ve manufacturing ceramic reinforced polymer (Lava TM
Ul0mate, 3M ESPE, St. Paul, NM, USA), and 2 different addi0ve manufacturing resin materials
for defini0ve restora0ons; 1 (VarseoSmile Crown Plus, Bego, Lincoln, Rhode Island) , 2 (Ceramic
Crown, Sprintray, Los Angeles, CA, USA). The composi0on of the materials used in this study
are exposed in Table 2. The samples were fabricated, and a standard polishing surface was
performed on all the samples. The samples were acached to an interchangeable system to ease
the posi0oning of the samples during surface analysis. The samples were then leh for at least
24 hours in dry ambient condi0ons. Wear simula0on was performed with a dual-axis chewing
simulator (CS-8, SD Mechatronic, Feldkirchen-Westerham, Germany) for 120,000 cycles,
applying 5kg of force on each bar with a 0.7mm sliding movement at a frequency of 1.6Hz in
dis0lled water using an antagonist made of Empress CAD. The samples and the antagonists
were analyzed with a surface op0cal scanner to evaluate volumetric loss and maximum wear
depth at different stages of the process. Final profilometry was performed on the samples.

40
Table 2: Materials composi8on
Material
Commercial
Name and
Lot nº
Composi0on Manufacturer
Manufacturing
method
Nanofilled
milled resin
nano ceramic
composite
Lava Ultimate
N642103
The fillers consist of a
combina2on of nonagglomerated/nonaggregated 20 nm silicon
oxide fillers, nonagglomerated/nonaggregated 4 to 11 nm
zirconium dioxide fillers
and aggregated zirconium
oxide / Silicon oxide
cluster (consis2ng of 20
nm silicon oxide and 4 to
11 nm zirconium dioxide
par2cles). 80% (weight
frac2on) Dimethacrylate
resin (TEGDMA, bisGMA,
bisEMA, UDMA)
3M ESPE
Subtrac2ve
manufacturing
3D Printed
Composite
Resin
VarseoSmile
Crown Plus
LOT 600577
Esterifica2on products of
4,0 isopropylidiphenol,
ethoxylated and 2-
methylprop-2enoic acid,
methyl benzoylformate,
diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide
(TPO). Total fillers by
weight 30-50%, silanized
dental glass 0.7 µm.
Bego
Addi2ve
manufacturing
3D Printed
Composite
Resin
Ceramic
crown
S23C14CA11
Mixture of methacrylic
acid esters, photo
ini2ators, proprietary
pigment, and addi2ve
package. 50 % inorganic
ceramic content by
weight.
Sprintray
Addi2ve
manufacturing
Silicate ceramic
IPS Empress
CAD mul2
LOT T39745
Glassy matrix and leucite
crystals homogeneous
distribu2on of leucite
crystals diameter of the
crystals is 1 – 5 μm, the
crystal phase volume is
35–45 % by volume.
Ivoclar
Vivadent
Subtrac2ve
manufacturing

41
2.2. Sample fabrica-on
2.2.1. Subtrac0ve manufactured material
In Group 1 (Control), Lava TM Ul0mate (3M ESPE, St. Paul, NM, USA) Shade D2-LT (Figure 12).
Lot nº N642103.
CAD-CAM blocks made from ceramic-reinforced polymer
(Lava TM Ul0mate, 3M ESPE, St. Paul, NM, USA, 14 mm x
14 mm x 18 mm) were sliced using a precision low-speed
diamond saw (IsoMet 1000, Buehler, Lake Bluff, IL, USA)
Figure 10 under dis0lled water for constant cooling at a
constant speed of 500rpm using a diamond blade (102mm
diameter, 0.3 mm thickness; IsoMet Blade 15LCA, Buehler,
Lake Buff, IL, USA). The block was first measured Figure 11 and then a calcula0on of how many
samples would be possible to create out of each block was made as shown in Figure 13. A total
of 8 slices in the shape of flat squares with dimensions of 14 mm x 14 mm x 3 mm were
obtained. Two blocks were used to create a total of 8 samples following the measurements as
represented in Figure 13. Ini0al slice was
Figure 12: Lava Ul8mate Block
Figure 11: Lava Ul8mate CAD / CAM block
measurements
Figure 10: IsoMet Precision Saw

42
intended to achieve a calibra0on of the diamond saw and then proceed with the remaining
slices.
Figure 13: Es8ma8on of samples per block
2.2.2. Addi0vely manufactured material:
For all addi0vely manufactured materials, an
open-source prototype design sohware based on
high-resolu0on dynamic triangle meshes
(Meshmixer, Autodesk, San Francisco, CA, USA)
was used to design a flat square object
measuring 14 mm x 14 mm x 3 mm. The resul0ng
Figure 14:STL file of the sample for prin8ng

43
3D object was exported to a standard tessella0on language (STL) file for the printed resin
groups Figure 14.
Group 2: Resin 1, (VarseoSmile Crown Plus, Bego,
Lincoln, Rhode Island) Color A1 Figure 15.
- Slicing: The STL file was imported into a slicer
program (Rayware, Sprintray, Los Angeles, CA, USA)
to create a prin0ng file. The digital sample was
angled at 45 degrees with automa0c func0on
supports at the center of the prin0ng bed of the 3D
printer, using the predetermined exposure seqngs
for the resin with a layer thickness of 50µm. Eight
samples were arranged on the virtual printer bed.
The resul0ng file was transferred to a 3D printer, a
DLP printer (Sprintray Pro 95, Los Angeles, CA, USA)
Figure 16.
Figure 16: Slicing program (RayWare) before sending the job to the printer VarseoSmile Crown Plus
Figure 15: VarseoSmile Crown Plus boZle

44
- Prin0ng: The bocle containing the resin (VarseoSmile Crown Plus, Bego, Lincoln, Rhode Island)
was ac0vely hand shaken for 2 minutes before pouring it into the printer vat. Then, the objects
were printed at the predetermined seqngs.
- Post-processing: Aher removing the printed samples from the 3D printer plaorm using a
stainless-steel spatula (Sprintray, Los Angeles, CA, USA) Figure 17, the supports were removed
with pliers (Sprintray, Los Angeles, CA, USA). The samples were pre-cleaned in an unheated
ultrasonic bath (Ultrasonic Cleaning Systems,
Quantrex, Kearny, NJ, USA) with 96% ethanol
(Solimo, Seacle, Washington USA) for 3 min.
Aher the pre-cleaning, a second clean was
performed with fresh 96% ethanol (Solimo,
Seacle, Washington USA) in an unheated
ultrasonic bath (Ultrasonic Cleaning Systems,
Quantrex, Kearny, NJ, USA) for 2 min Post-cure
for addi0onal UV-light curing was performed (Sprint Ray ProCure, Sprint Ray, Los Angeles, CA,
United States) for two cycles of 20 min at 20 ºC.
Figure 17: 3D Printed VarseoSmile Crown Plus

45
Figure 18: Addi8ve manufacturing workflow

Group 3: Resin 2 (Ceramic Crown, Sprintray, Los Angeles, CA, USA), Color A1 Figure 19.
- Slicing: The STL file was imported into a slicer program
(Rayware, Sprintray, Los Angeles, CA, USA) to create a prin0ng
file. The digital sample was angled at 45 degrees with automa0c
func0on supports at the center of the prin0ng bed of the 3D
printer, using the predetermined exposure seqngs for the resin
at 50µm layer thickness. 4 samples were arranged on the virtual
printer bed; thus, two different prints were needed to fabricate
the 8 needed samples. The resul0ng file was transferred to a 3D
printer, a stereolithography (SLA) printer (Sprintray Pro 95S, Los
Angeles, CA, USA) (Figure 20). Figure 19: Ceramic Crown boZle

46
Figure 20: Sliceing program (RayWare) before sending the job to the printer Ceramic Crown
- Prin0ng: The bocle containing the resin (Ceramic Crown, Sprintray, Los Angeles, CA, USA) was
ac0vely hand shaken for 2 min before pouring it into the printer vat. Then, the objects were
printed at the predetermined seqngs.
- Post-processing: Aher removing
the printed samples from the 3D
printer plaorm with a stainlesssteel spatula (Sprintray, Los
Angeles, CA, USA), the supports
were removed with pliers
(Sprintray, Los Angeles, CA, USA)
(Figure 21). The samples were
pre-cleaned in an unheated bath
(ProWash S, Sprintray, Los Figure 21: Ceramic Crown sample before removal of the supports

47
Angeles, CA, USA) with 96% ethanol (Solimo, Seacle, Washington USA) for 3 minutes. Aher the
pre-cleaning, a second clean was performed with fresh 96% ethanol (Solimo, Seacle,
Washington USA) in an unheated bath for 3 min. Then, the samples were rinsed with clean
ethanol to remove any loosely acached resin. The samples were dried with the automated
post-processing system (ProWash S, Sprintray, Los Angeles, CA, USA) for 7 min. Post-cure for
addi0onal UV-light curing was performed (Sprint Ray ProCure 2, Sprint Ray, Los Angeles, CA,
United States) using the predetermined seqngs for the resin (Figure 18).
2.2.3. Polishing
In all groups, the polishing of the samples was carried out to eliminate surface irregulari0es and
standardize the wear surface. The opposing surface of the sample was not subjected to
polishing. The wear surface underwent a polishing process using the following materials:
- 600-grit sandpaper CarbiMet® Plain 600 [P1200] (Buehler Ltd., Lake Bluff, IL, USA)
- 1000-grit sandpaper CarbiMet® Plain 1000 [P2500] (Buehler Ltd., Lake Bluff, IL, USA)
- 1200-grit sandpaper MicroCut® Plain 1200 [P2500] (Buehler Ltd., Lake Bluff, IL, USA)
This polishing was performed under running dis0lled water.
2.2.4. Interchangeable moun0ng system
Each sample was affixed to interlocking plas0c bricks-plas0c 0les (2 x 2 id. 306801/3068, color
white, Lego, Billund, Denmark) using polyurethane adhesives (Gorilla glue, Sharonville, Ohio)
(Figure 23). A corresponding modular plate with protruding reten0on knobs (plate 2x2, id.
302201/3022, color white, Lego, Billund, Denmark) was embedded into a circular holder using
acrylic resin. The 0le with the affixed sample was then acached to the embedded plate. This
assembly was installed in a dual-axis chewing simulator. The use of this modular system

48
simplified the installa0on and removal of the sample in and from the chewing simulator. An
open space was leh available to facilitate easy detachment of the samples when necessary
Figure 22.
Figure 22: Interchangeable moun8ng system
Figure 23: Sample moun8ng to the interchangeable system

49
The samples were marked with 3 round indenta0ons on one of the corners of the surface using
a small carbide (1 HP round carbide H1.11.008 bur, Brasseler USA, Savannah, GA, USA) at
20,000 rpm to facilitate overlapping and scanning of the samples Figure 24.
Figure 24: Indenta8ons on the surface of the samples to facilitate scanning and overlapping
For the scanner, a holder with an acached modular plate featuring protruding reten0on knobs
(plate 2x2, id. 302201/3022, color white) was used to allow the acachment of the 0le/sample
for scanning, providing extra references to the scanner for the scanning process Figure 25.

50
Figure 25: Scanning pla[orm
2.2.5. Antagonists
Antagonists were fabricated from leucitereinforced glass ceramic CAD-CAM blocks
(Empress CAD mul0, Ivoclar Vivadent, Schaan,
Liechtenstein) Figure 27. To create these
antagonists, a sphere-shaped object with a
diameter of 2.36 mm at a height of 0.6 mm
was designed using (Meshmixer, Autodesk,
San Francisco, CA, USA) Figure 26.
Figure 26:STL file of the antagonist

51
The resul0ng 3D object was exported to an STL file
and imported to the milling sohware (inLab, Dentsply
Sirona, Charloce, NC). The file was milled using a 3-
axis CAD/CAM milling unit (CEREC MC XL, Dentsply
Sirona, Charloce, NC). Each ceramic block (Empress
CAD mul0, Ivoclar Vivadent, Schaan, Liechtenstein)
Figure 27, allowed to posi0on two antagonists to be
milled simultaneously. A total of 24 antagonists were
milled using 12 different CAD / CAM blocks.
The sphere-shaped surface of the antagonist was
polished using intraoral ceramic polishers (K0305
Dialite Feather Lite All Ceramic Adjus0ng & Polishing System, Brasseler, Savannah, GA, USA).
This polishing was carried out with a contra-angle handpiece mounted on an electric motor
Figure 27: Empress CAD Mul8

52
(Bien air) at a speed of 4,000 rpm and a torque of 3.50 Ncm for 20 s Figure 28 Error! Reference
source not found..
Figure 28: Antagonist manufacturing process
The milled antagonist was then mounted into the
chewing simulator antagonist holders using packable
light-curing composite (Simplishade, KaVo Kerr, Brea,
CA, USA) and light cured for 20 s for each increment
using a dual wavelength LED intraoral curing device
(VALO corded, Ultradent, South Jordan, UT, USA),
using standard power mode (Figure 29).
The antagonists were marked with 3 round
indenta0ons on one of the corners of the surface
using a small carbide (1 HP round carbide H1.11.008
Figure 29: Empress CAD antagonist mounted in
the chewing simulator mount

53
bur, Brasseler USA, Savannah, GA, USA) at 20,000 rpm to facilitate overlapping and scanning of
the samples.
2.3. Wear simulator
To simulate wear on the wear surface of the samples, a dual-axis chewing simulator (CS-8, SD
Mechatronic, Feldkirchen-Westerham, Germany) was employed (Figure 30).
Figure 30: dual-axis chewing simulator (CS-8, SD Mechatronic, Feldkirchen-Westerham, Germany)
Before conduc0ng the wear simula0on, the samples were kept dry for a minimum of 24 h to
ensure that the glue used for acachment had set completely.
For the wear simula0on process, the mounts for the samples were placed in the chewing
simulator and filled with dis0lled water. The antagonist was lowered onto the flat surface of the
sample to establish the baseline posi0on.
The following seqngs were used for the chewing simulator:
- 5kg force applied to each bar / 49N

54
- A sliding movement of 0.7mm forward/backward at a speed of 7.0 mm/s
- A frequency of 1.6Hz
The simula0on consisted of a total of 120,000 cycles, conducted in sets of 30,000 cycles each.
Aher comple0ng each cycle set, the sample was removed from the designed holder for surface
scanning. Following the surface scanning, the sample was remounted in the exact same
posi0on using the interchangeable system for subsequent cycles. The device stopped at 30,000
cycles, 60,000 cycles, 90,000 cycles and finally at 120,000 cycles.
2.4. Volumetric loss and ver-cal loss data acquisi-on for the samples and
antagonists
For the acquisi0on of volumetric loss data, an intraoral op0cal scanner u0lizing 3D video mo0on
technology (Medit I 700, Medit, Seoul, South Korea) was employed. This scanner is equipped
with a reported accuracy of 10.9µm ± 0.98µm and was operated in high-defini0on (HD) mode
to generate unmodified STL files (137).
To achieve consistency between all the scans, before each set of cycles, the scanner was
calibrated. Same 0p and same scanner device were used to perform all the surface scans. The
samples were then mounted in the interchangeable device and same pacern was followed in
all the scans maintaining a close scanning distance of 2mm, all the surface scans were
performed by the same trained operator following a precise sequence as represented in Figure
31. The antagonists were scanned in the chewing simulator to avoid modifying the original
posi0on, for the antagonists, the following scanning pacern was followed as shown in Figure
32.

55
Figure 31: Scanning sequence of the samples
Figure 32: Scanning sequence of the antagonist

56
2.5. Volumetric loss analysis
To analyze the volumetric loss at various stages of wear, specialized sohware for 3D measuring
data analysis (Meshmixer, Autodesk, San Francisco, CA, USA) was u0lized. STL files were
imported to the sohware. The original mesh was ini0ally cleaned so that only the sample scan
would remain. The open mesh was ini0ally cleaned to remove all excess data, then the mesh
was closed as shown in Figure 33, and volume was noted. Aher virtually flacening the eroded
defect using the fill op0on, the volume was noted once more. The following mathema0cal
formula was used to achieve the final volumetric loss (138) (Volume of the flacened sample –
Volume of the worn sample = lost volume) as shown in the example in Figure 34.
Figure 33: Cleaning process of original open mesh STL file to final closed STL file

57
Figure 34: Volumetric loss analysis example
2.6. Ver-cal loss analysis
Sohware for analyzing 3D measuring data (GOM inspect, Zeiss, Oberkochen, Germany) was
used to overlap the data with the baseline scan and calculate the ver0cal loss at 30,000 cycles,
60,000 cycles and 90,000 cycles and 120,00 cycles. The deepest point was selected by the
sohware as shown in the example Figure 35.

58
Figure 35: GOM Inspect Overlap and deepest point selec8on
The following moments were chosen for data acquisi0on:
1. Baseline Data: Scanning was performed using the intraoral scanner Medit I 700.
2. 30,000 Cycles: Scanning was performed using the intraoral scanner Medit I 700.
3. 60,000 Cycles: Scanning was performed using the intraoral scanner Medit I 700.
4. 90,000 Cycles: Scanning was performed using the intraoral scanner Medit I 700.
5. Final Data at 120,000 Cycles: Scanning was performed using the intraoral scanner Medit I
700 and the profilometer.
This data acquisi0on strategy allowed for the measurement and analysis of volumetric loss at
each specified stage of the wear simula0on process.

59
2.7. Cross-Sec-on analysis with Profilometry
White light confocal displacement sensor (Acuity CSS PRIMA, Schmic industries, Portland, OR)
was used to perform cross-sec0on and longitudinal final scans of the wear pacerns for all the
samples. The scanning 0p used was the Acuity Ini0al 0.4 (Acuity CSS PRIMA, Schmic industries,
Portland, OR) with a reported accuracy from the manufacturer of 80nm.
The samples were acached to the scanning surface of the device with double sided tape. The
ver0cal posi0on of the scanning device was set manually un0l the scanner was set between the
scanning range of the profilometer.
The following parameters were used to scan the surface of the samples in both longitudinal
and transversal cross-sec0ons of the worn areas:
X axis = 1000 pixel / mm
Sampling rate 200 Hz
(Figure 36).
Figure 36: Cross sec8on profilometry

60
2.8. Sample and document iden-fica-on
The samples were marked with a number on one of the corners using a small carbide (1 HP
round carbide H1.11.008 bur, Brasseler USA, Savannah, GA, USA) at 20,000 rpm.
The samples and antagonists were labeled with unique numbers.
The following tables provides the number iden0fica0on that was used for the samples and
antagonists (Table 3, Table 4) :
Table 3: Iden8fica8on codes used for the samples
SAMPLES 1 2 3 4 5 6 7 8
LAVA
ULTIMATE L1 L2 L3 L4 L5 L6 L7 L8
CERAMIC
CROWN C1 C2 C3 C4 C5 C6 C7 C8
VARSEOSMILE V1 V2 V3 V4 V5 V6 V7 V8
Table 4: Iden8fica8on codes used for the antagonists
ANTAGONISTS 1 2 3 4 5 6 7 8
LAVA
ULTIMATE LA1 LA2 LA3 LA4 LA5 LA6 LA7 LA8
CERAMIC
CROWN CA1 CA2 CA3 CA4 CA5 CA6 CA7 CA8
VARSEO VA1 VA2 VA3 VA4 VA5 VA6 VA7 VA8

61
The resul0ng STL files from the op0cal scanning of the samples and antagonists were labeled
with unique file names.
The following tables provides the file name that was used for the STL resul0ng from the
scanning of the samples, Table 5, Table 6, Table 7, Table 8, Table 9, Table 10.
Table 5: File names used for Lava Ul8mate STL files
LAVA
ULTIMATE 1 2 3 4 5 6 7 8
Baseline L1B L2B L3B L4B L5B L6B L7B L8B
30,000
cycles L13 L23 L33 L43 L53 L63 L73 L83
60,000
cycles L16 L26 L36 L46 L56 L66 L76 L86
90,000
cycles L19 L29 L39 L49 L59 L69 L79 L89
120,000
cycles L1F L2F L3F L4F L5F L6F L7F L8F

62
Table 6: File names used for Ceramic Crown STL files
CERAMIC
CROWN 1 2 3 4 5 6 7 8
Baseline C1B C2B C3B C4B C5B C6B C7B C8B
30,000
cycles
C13 C23 C33 C43 C53 C63 C73 C83
60,000
cycles C16 C26 C36 C46 C56 C66 C76 C86
90,000
cycles C19 C29 C39 C49 C59 C69 C79 C89
120,000
cycles C1F C2F C3F C4F C5F C6F C7F C8F
Table 7: File names used for VarseoSmile Crown Plus STL files
VARSEOSMILE 1 2 3 4 5 6 7 8
Baseline V1B V2B V3B V4B V5B V6B V7B V8B
30,000 cycles V13 V23 V33 V43 V53 V63 V73 V83
60,000 cycles V16 V26 V36 V46 V56 V66 V76 V86
90,000 cycles V19 V29 V39 V49 V59 V69 V79 V89
120,000
cycles V1F V2F V3F V4F V5F V6F V7F V8F

63
Table 8: File names used for Lava Ul8mate Antagonists STL files
LAVA
ULTIMATE
ANTAGONIST
1 2 3 4 5 6 7 8
Baseline LA1B LA2B LA3B LA4B LA5B LA6B LA7B LA8B
30,000
cycles
LA13 LA23 LA33 LA43 LA53 LA63 LA73 LA83
60,000
cycles LA16 LA26 LA36 LA46 LA56 LA66 LA76 LA86
90,000
cycles LA19 LA29 LA39 LA49 LA59 LA69 LA79 LA89
120,000
cycles LA1F LA2F LA3F LA4F LA5F LA6F LA7F LA8F

Table 9: File names used for Ceramic Crown Antagonists STL files
CERAMIC
CROWN
ANTAGONIST
1 2 3 4 5 6 7 8
Baseline CA1B CA2B CA3B CA4B CA5B CA6B CA7B CA8B
30,000
cycles
CA13 CA23 CA33 CA43 CA53 CA63 CA73 CA83
60,000
cycles CA16 CA26 CA36 CA46 CA56 CA66 CA76 CA86
90,000
cycles CA19 CA29 CA39 CA49 CA59 CA69 CA79 CA89
120,000
cycles CA1F CA2F CA3F CA4F CA5F CA6F CA7F CA8F

64
Table 10: File names used for VarseoSmile Crown Plus Antagonists STL files
VARSEOSMILE
ANTAGONIST 1 2 3 4 5 6 7 8
Baseline VA1B VA2B VA3B VA4B VA5B VA6B VA7B VA8B
30,000 cycles VA13 VA23 VA33 VA43 VA53 VA63 VA73 VA83
60,000 cycles VA16 VA26 VA36 VA46 VA56 VA66 VA76 VA86
90,000 cycles VA19 VA29 VA39 VA49 VA59 VA69 VA79 VA89
120,000
cycles VA1F VA2F VA3F VA4F VA5F VA6F VA7F VA8F

2.9. Sta-s-cs
All data collected was recorded from the different sohware: Data for the maximum ver0cal loss
from the (GOM inspect, Zeiss, Oberkochen, Germany), and the volumetric loss from the
(Meshmixer, Autodesk, San Francisco, CA, USA). The data was collected and organized in a
digital spreadsheet using Excel (Microsoh Corp, Redmond, WA, USA).
Volumetric loss was measured in mm3
.
The ver0cal loss was measured in µm.
Quan0ta0ve variables are described by the Mean, Standard Devia0on (SD), range (MinimumMaximum), Standard Error (SE), and 95% confidence interval of the mean. Sta0s0cal analysis

65
was carried out using Sta0s0cal Package for Social Sciences (SPSS) version 28.0.0.0. for Mac
(IBM SPSS Sta0s0cs, IBM Corp., USA).
Normality of the data was calculated.
Ini0ally, an assessment of the normality of the data was conducted since it serves as a
prerequisite for applying sta0s0cal tests. To determine whether our data followed a normal
distribu0on, the Shapiro-Wilk test was used to test the normality hypothesis of the volumetric
loss data and ver0cal loss data. The Levene’s test was then used to check the homogeneity of
the variances.
As the Levene’s tests showed non homogeneity of the data (p<0.05), the Non-parametric
Kruskal-Wallis test was applied with a Bonferroni correc0on by mul0plica0on of the p-values by
the number of comparisons, maintaining the level of significance at ⍺=0.05.

66
Chapter 3: Results
3.1. Images of the op-cal scans
The following images of the STL files can be seen for the different materials and different
number of cycles (Figure 37), (Figure 38), (Figure 39).
Figure 37: Images of the STL files of Lava Ul8mate

67
Figure 38: Images of the STL files of VarseoSmile Crown Plus

68
Figure 39: Images of the STL files of Ceramic Crown
3.2. Images of the profilometry aVer 120,000 cycles
The following images of the profilometry can be seen for the different materials at 120,000
cycles. (Figure 40), (Figure 41), (Figure 42).

69
Figure 40: Profilometry for Lava Ul8mate

70
Figure 41: Profilometry for VarseoSmile Crown Plus

71
Figure 42: Profilometry for Ceramic Crown

72
3.3. Descrip-ve analysis of the Volumetric Loss of the samples
A summary of the descrip0ve sta0s0cal analysis showing the mean volumetric loss of the
materials depending on the material and at different cycles the samples were tested can be
seen in Figure 43.
Overall, the highest mean volumetric loss at 120,000 cycles was registered in the VarseoSmile
Crown Plus group (-0.17088 ± 0.074756 mm3
). The lowest mean in the volumetric loss aher
120,000 cycles was seen in the Ceramic Crown group (0.03600 ± 0.009442 mm3
) as seen in
Table 11.
Figure 43: Overall mean volumetric loss (mm3)
Lava Ul0mate presented the least amount of wear aher 30,000 cycles (-0.02650 ± 0.007426
mm3
) if baseline is not taken into considera0on. The highest amount of volumetric loss mean
was seen aher the comple0on of the 120,000 cycles (-0.13238 ± 0.031487 mm3
).

73
VARSEOSMILE CROWN PLUS presented the least amount of wear aher 30,000 cycles (-0.06100±
0.028685 mm3
) if baseline is not taken into considera0on. The highest amount of volumetric
loss mean was seen aher the comple0on of the 120,000 cycles (-0.17088 ± 0.074765 mm3
).
CERAMIC CROWN presented the least amount of wear aher 30,000 cycles (0.02675 ± 0.016158
mm3
) if baseline is not taken into considera0on. The highest amount of volumetric loss mean
was seen aher 90,000 cycles (0.04025 ± 0.016876 mm3
).
Table 11: Overall volumetric loss (mm3) of Lava Ul8mate, VarseoSmile Crown Plus and Ceramic Crown

74
3.3.1. Data normality analysis and equality of variances of volumetric loss
The Shapiro-Wilk test was used to test the normality of the volumetric loss values. Aher the
test was applied, it was revealed that the data was not normally distributed as only 3 out of the
15 groups deviated from the normality assump0on (p<0.05) Table 12.
Table 12: Shapiro-Wilk test for the Volumetric loss (normality)
Then, the Levene’s test was applied to evaluate the homogeneity of the data, showing that the
variances were not homogeneous (p<0.001) Table 13.
Table 13: Levene's test (equality of variances)

75
3.4. Comparison between materials
3.4.1. Volumetric loss between different materials
Table 14: Overall material mean, standard devia8on, maximum and minimum values
When the materials are compared to each other, without taking into considera0on the amount
of cycles, Ceramic Crown showed the least amount of volumetric loss (0.02725 ± 0.018500
mm3
), followed by the Lava Ul0mate material (-0.06198 ± 0.051156 mm3
) and finally, the
material showing the most amount of wear is the VarseoSmile Crown Plus (-0.09693 ± 0.079577
mm3
) Table 14 Error! Reference source not found..
Figure 44: Independent-Samples Kruskal-Wallis Test for Materials

76
The Non-parametric KruskalWallis Test showed that there
was significant difference
between the different tested
materials. (p=0.000) for the
independent samples analysis as seen in Figure 44
For the pairwise comparison, the results showed that there was significant between the Lava
Ul0mate and the Ceramic Crown (p=0.000) and between the VarseoSmile Crown Plus and the
Ceramic Crown (p=0.000). There appeared to be no difference between the VarseoSmile Crown
Plus and the Lava Ul0mate (P=0.570) Figure 45, Table 15
Figure 45: Pairwise comparison of the materials volumetric loss
Table 15: Overall pairwise comparison between materials

77
In the ceramic crown group, theSTL files and the data show a gain in volumetric loss instead of
loss as seen in the following Figure 46. This is only consistent in the Ceramic Crown group. The
samples were then evaluated visually to check if there was gain in the samples, as there
appeared to be no material gain in the samples, a profilometry was used to look for the actual
loss of material as seen in Figure 47. Profilometry confirmed a loss of material in all the samples.
Figure 46: STL file from Ceramic Crown showing material ar8fact.
Figure 47: Ceramic Crown profilometry

78
3.4.2. Volumetric loss between different materials aher 120,000 cycles
Table 16: Material mean, standard devia8on, maximum and minimum for volumetric loss
When the materials are compared to each other at the end of the test, 120,000 cycles, Ceramic
Crown showed the least amount of volumetric loss (0.03600± 0.009442 mm3
), followed by the
Lava Ul0mate material (-0.13238 ± 0.031487 mm3
) and finally, the material showing the most
amount of wear is the VarseoSmile Crown Plus (-0.17088 ± 0.074765 mm3
) Table 16.
Figure 48: Independent-Samples Kruskall-Wallis Test

79
The Non-parametric Kruskal-Wallis Test showed that there was significant difference between
the different tested materials. (p=0.000)
for the independent samples analysis as
seen in Figure 48.
For the pairwise comparison, the results
showed that there was significant between
the Lava Ul0mate and the Ceramic Crown (p=0.008) and between the VarseoSmile Crown Plus
and the Ceramic Crown (p=0.000). There appeared to be no sta0s0cal difference between the
VarseoSmile Crown Plus and the Lava Ul0mate (P=1.000) Figure 49, Table 17.
Table 17: Overall Pairwise comparison between materials at
120,000 cycles
Figure 49: Pairwise comparison between materials at 120,000 cycles

80
3.5. Comparison between cycles
3.5.1. Volumetric loss depending on cycles for all materials.
Table 18: Mean, Standard devia8on, maximum and minimum from cycles volumetric loss.
When the different cycle 0mepoints are compared to each other regardless of the material, 0
cycles showed the least amount of volumetric loss (0.000 ± 0.000 mm3
), followed by 30,000
cycles (-0.02025 ± 0.002 mm3
), 60,000 cycles (-0.04779 ± 0.005 mm3
), 90,000 cycles (-0.06229
± 0.008 mm3
) and the 120,000 cycles showing the most amount of volumetric loss (-0.08908 ±
0.010 mm3
)
Table 18
Figure 50: Independent-samples Kruskall-Wallis Test

81
The Non-parametric Kruskal-Wallis Test showed
that there was significant difference between the
different tested materials. (p=0.017) for the
independent samples analysis as seen in Figure
50.
For the pairwise comparison, the results showed
that there was only sta0s0cal significance when the baseline (0 cycles) is compared to the result
aher the wear has been tested aher 120,000 cycles (p=0.020). The other pairwise comparisons
did not show any sta0s0cal significance (p<0.05) Figure 51, Table 19.
Figure 51: Pairwise comparison between different cycles.
Table 19:Overall pairwise comparison between cycles

82
3.5.2. Volumetric loss depending on cycles for LAVA ULTIMATE
Table 20: Mean, Standard devia8on, maximum and minimum from cycles volumetric loss.
When the different cycle 0mepoints are compared to each other for Lava Ul0mate, 0 cycles
showed the least amount of volumetric loss (0.000 ± 0.000 mm3
), followed by 30,000 cycles (-
0.02650 ± 0.007426 mm3
), 60,000 cycles (-0.05575 ± 0.011793 mm3
), 90,000 cycles (-0.09525
± 0.024341 mm3
) and the 120,000 cycles showing the most amount of volumetric loss (-
0.13238 ± 0.031487 mm3
) Table 20.
Figure 52: Independent-samples Kruskall-Wallis Test

83
The Non-parametric Kruskal-Wallis Test showed
that there was significant difference between the
different tested materials. (p=0.000) for the
independent samples analysis as seen in Figure 52.
For the pairwise comparison, the results showed
that there was sta0s0cal significance between the
120,000 cycles and the 30,000 cycles (P=0.001), between the 120,000 cycles and baseline
(P=0.000), between 90,000 cycles and 30,000 cycles (P=0.033), 90,000 cycles and baseline
(P=0.000). For the rest of the pairwise comparisons there was not sta0s0cal difference Table
21, Figure 53.
Figure 53: Pairwise comparison between different cycles.
Table 21: Overall pairwise comparison between cycles

84
3.5.3. Volumetric loss depending on cycles for VARSEOSMILE CROWN PLUS
Table 22: Mean, Standard devia8on, maximum and minimum from cycles volumetric loss.
When the different cycle 0mepoints are compared to each other for VarseoSmile Crown Plus,
0 cycles showed the least amount of volumetric loss (0.000 ± 0.000 mm3
), followed by 30,000
cycles (-0.06100 ± 0.028685 mm3
), 60,000 cycles (-0.12088 ± 0.056034 mm3
), 90,000 cycles (-
0.13188 ± 0.072217 mm3
) and the 120,000 cycles showing the most amount of volumetric loss
(-0.17088 ± 0.074765 mm3
) Table 22.
Figure 54: Independent-samples Kruskall-Wallis Test

85
The Non-parametric Kruskal-Wallis Test showed
that there was significant difference between
the different tested materials. (p=0.000) for the
independent samples analysis as seen in Figure
54.
For the pairwise comparison, the results showed
that there was sta0s0cal significance between
the 120,000 cycles and the 30,000 cycles (P=0.029), between the 120,000 cycles and baseline
(P=0.000), between 90,000 cycles and baseline (P=0.002), 60,000 cycles and baseline
(P=0.004). For the rest of the pairwise comparisons there was not sta0s0cal difference Figure
55, Table 23.
Figure 55: Pairwise comparison between different cycles.
Table 23: Overall pairwise comparison between cycles

86
3.5.4. Volumetric loss depending on cycles for CERAMIC CROWN
Table 24: Mean, Standard devia8on, maximum and minimum from cycles volumetric loss.
When the different cycle 0mepoints are compared to each other for Ceramic Crown, this
material showed increase in volume, with the most increase in volume aher 90,000 cycles
(0.04025 ± 0.016876 mm3
), followed 120,000 cycles (0.03600 ± 0.009442 mm3
), 60,000 cycles
(0.03325 ± 0.010053 mm3
), 30,000 cycles (0.02675 ± 0.016158 mm3
) Table 24.
Figure 56: Independent-samples Kruskall-Wallis Test

87
The Non-parametric Kruskal-Wallis Test showed that there was significant difference between
the different tested materials. (p=0.000) for the independent samples analysis as seen in Figure
56.
Table 25: Overall pairwise comparison between cycles
For the pairwise comparison, the results
showed that there was sta0s0cal significance
between the Baseline and the 60,000 cycles
(P=0.008), between the 120,000 cycles and
baseline (P=0.002), between 90,000 cycles and
baseline (P=0.001). For the rest of the pairwise
comparisons there was not sta0s0cal difference
(Figure 57, Table 25).
Figure 57: Pairwise comparison between different cycles

88
3.6. Comparison between chambers
3.6.1. Volumetric loss between chambers for all materials.
Table 26: Mean, Standard devia8on, maximum and minimum from chamber volumetric loss.
When the different chambers are compared regardless of the material and the cycles, the
chamber with the most volumetric loss was the chamber 1 (-0.08300 ± 0.125382 mm3
), and
the one with the least amount of volumetric loss was chamber 4 (-0.02800 ± 0.044667 mm3
)
Table 26.
Figure 58: Independent-samples Kruskall-Wallis Test

89
The Non-parametric Kruskal-Wallis Test showed that there
was no significant difference between the different tested
materials. (p=0.996) for the independent samples analysis.
Figure 58
For the pairwise comparison, the results showed that there
was no sta0s0cal significance between any of the
chambers that were tested.(Table 27, Figure 59)
Table 27: Overall pairwise comparison
between chambers
Figure 59: Pairwise comparison between different cycles

90
3.7. Descrip-ve analysis of the Ver-cal Loss of the samples
A summary of the descrip0ve sta0s0cal analysis showing the mean volumetric loss of the
materials depending on the material and at different cycles the samples were tested in for the
volumetric loss as seen in Figure 60.
For the ver0cal loss, aher 120,000 cycles, the most ver0cal loss was for the VarseoSmile
Crown Plus Group (-87.5 ± 13.89 µm) and the least ver0cal loss was recorded for the Ceramic
Crown (-3.8 ± 13.02 µm ) Table 28.
Figure 60: Overall mean ver8cal loss (µm)
LAVA ULTIMATE presented the least amount of ver0cal loss aher 30,000 cycles (-26.3 ± 9.16 µm
) if baseline is not taken into considera0on. The highest amount of volumetric loss mean was
seen aher the comple0on of the 120,000 cycles (-87.5 ± 13.89 µm ).

91
VARSEOSMILE CROWN PLUS presented the least amount of wear aher 60,000 cycles (-116.3 ±
24.46 µm ) if baseline is not taken into considera0on. The highest amount of volumetric loss
mean was seen aher the comple0on of the 120,000 cycles (-248.8 ± 264.06 µm ).
CERAMIC CROWN presented the least amount of wear aher 30,000 cycles (1.3 ± 8.35 µm ) if
baseline is not taken into considera0on. The highest amount of volumetric loss mean was seen
aher 60,000 cycles (-5.0 ± 9.26 µm ).
Table 28: Overall Ver8cal loss (µm) of Lava Ul8mate, VarseoSmile Crown Plus and Ceramic Crown

92
3.7.1. Data normality analysis and Equality of variances of ver0cal loss
The Shapiro-Wilk test was used to test the normality of the volumetric loss values. Aher the
test was applied, it was revealed that the data was not normally distributed as only 3 out of
the 15 groups deviated from the normality assump0on (p<0.05) Table 29.
Table 29: Shapiro-Wilk test for the Ver8cal loss (normality)
Then, The Levene’s test was applied to evaluate the homogeneity of the data, showing that the
variances were not homogeneous (p<0.001) Table 30.
Table 30: Levene's test (equality of variances)

93
3.8. Comparison between materials
3.8.1. Ver0cal loss between different materials
Table 31: Mean, standard devia8on, maximum and minimum ver8cal loss (µm)
When the materials are compared to each other, without taking into considera0on the amount
of cycles, Ceramic Crown showed the least amount of ver0cal loss (-1.5 ± 9.21 µm), followed
by the Lava Ul0mate material (-48.0 ± 32.91 µm) and finally, the material showing the most
amount of wear is the VarseoSmile Crown Plus (-130.5 ± 177.11 µm) Table 31.
Figure 61: Independent-Samples Kruskal-Wallis Test Ver8cal loss

94
The Non-parametric Kruskal-Wallis
Test showed that there was significant
difference between the different
tested materials. (p=0.000) for the
independent samples analysis as seen
in Figure 61.
For the pairwise comparison, the results showed that there was significant between the Lava
Ul0mate and the Ceramic Crown (p=0.000), between the VarseoSmile Crown Plus and the
Ceramic Crown (p=0.000) and between the VarseoSmile Crown Plus and the Lava Ul0mate
(P=0.018) Figure 62, Table 32.
Table 32: Overall Pairwise comparison between materials at 120,000
cycles for ver8cal loss
Figure 62: Pairwise comparison between the different materials.

95
3.8.2. Ver0cal loss between different materials aher 120,000 cycles
Table 33: Overall material mean, standard devia8on, maximum and minimum values for ver8cal loss (µm)
When the materials are compared to each other at the end of the test, 120,000 cycles, Ceramic
Crown showed the least amount of volumetric loss (-38. ± 13.02 µm), followed by the Lava
Ul0mate material (-87.5 ± 13.89 µm) and finally, the material showing the most amount of wear
is the VarseoSmile Crown Plus (-248.8 ± 26.406 µm) Table 33.
Figure 63: Independent-Samples Kruskall-Wallis Test
The Non-parametric Kruskal-Wallis Test showed that there was significant difference between
the different tested materials. (p=0.000) for the independent samples analysis as seen in Figure
63.

96
For the pairwise comparison, the
results showed that there was no
significant between the Lava Ul0mate
and the Ceramic Crown (p=0.070) and
neither between the VarseoSmile
Crown Plus and the Lava Ul0mate (p=0.070). There appeared to be sta0s0cal difference
between the VarseoSmile Crown Plus and the Ceramic Crown (P=0.000) Figure 64, Table 34.
Table 34: Overall pairwise comparison between materials at 120,000
cycles
Figure 64: Pairwise comparison between the different materials at 120,000 cycles

97
3.8.3. Ver0cal loss of the antagonist between different materials
Table 35: Mean, Standard devia8on, maximum and mínimum from antagonists ver8cal loss (µm)
When the antagonists are compared to each other regardless of the cycles, Ceramic Crown
showed the least amount of volumetric loss (-40.8 ± 24.85 µm) together with the Lava Ul0mate
material (-40.8 ± 27.02 µm) and finally, the material showing the most amount of wear is the
VarseoSmile Crown Plus (-45.0 ± 33.74 µm) Table 35.
Figure 65: Independent-samples Kruskall-Wallis Test
The Non-parametric Kruskal-Wallis Test showed that there was no significant difference
between the different tested materials. (p=0.919) for the independent samples analysis as seen
in Figure 65.

98
For the pairwise comparison, the results
showed that there was no significant between
the Lava Ul0mate and the Ceramic Crown
(p=1.000), neither between the VarseoSmile
Crown Plus and the Lava Ul0mate (p=1.000)
and either appeared to be sta0s0cal difference between the VarseoSmile Crown Plus and the
Ceramic Crown (P=1.000) Figure 66, Table 36.
Table 36: Overall pairwise comparison between antagonists
Figure 66: Pairwise comparison between materials and antagonists.

99
3.9. Descrip-ve analysis of the Ver-cal Loss: Profilometry horizontal/ver-cal crosssec-on
A summary of the descrip0ve sta0s0cal analysis showing the mean ver0cal loss of the materials
as seen in Figure 67 for the horizontal cross sec0on.
For the ver0cal loss, aher 120,000 cycles for the horizontal cross sec0on, the most ver0cal
loss was for the VarseoSmile Crown Plus Group (-166.33 ± 37.33 µm) and the least ver0cal
loss was recorded for the Ceramic Crown (-18.76 ± 15.68 µm), Lava Ul0mate (-108.55 ± 11.90
µm) (Table 37).
Figure 67: Overall Ver8cal loss (µm) of Lava Ul8mate, VarseoSmile Crown Plus and Ceramic Crown
Table 37: Overall Ver8cal loss (µm) of Lava Ul8mate, VarseoSmile Crown Plus and Ceramic Crown

100
A summary of the descrip0ve sta0s0cal analysis showing the mean ver0cal loss of the materials
as seen in Figure 68 for the ver0cal cross sec0on.
Figure 68: Ver8cal loss (µm) Lava Ul8mate, VarseoSmile Crown Plus, Ceramic Crown ver8cal cross-sec8on
For the ver0cal loss, aher 120,000 cycles for the ver0cal cross sec0on, the most ver0cal loss
was for the VarseoSmile Crown Plus Group (-171.09 ± 34.35 µm) and the least ver0cal loss
was recorded for the Ceramic Crown (-21.18 ± 11.30 µm), Lava Ul0mate (-107.77 ± 12.65 µm)
(Table 38).
Table 38: Ver8cal loss (µm) Lava Ul8mate, VarseoSmile Crown Plus, Ceramic Crown Ver8cal cross-sec8on

101
3.9.1. Data normality analysis/Equality of variances of ver0cal loss-profilometry
The Shapiro-Wilk test was used to test the normality of the volumetric loss values. Aher the
test was applied, it was revealed that the data was not normally distributed as only 1 out of
the 6 groups deviated from the normality assump0on (p<0.05) Table 39.
Table 39: Shapiro - Wilk test for normality
Then, The Levene’s test was applied to evaluate the homogeneity of the data, showing that
the variances were homogeneous (p>0.001)Table 40, Table 41.
Table 40: : Levene's test (equality of variances) Horizontal Cross-sec8on
Table 41: : Levene's test (equality of variances) Ver8cal Cross-Sec8on

102
3.9.2. Ver0cal loss of the antagonist between different materials Horizontal crosssec0on
Table 42: Mean, Standard devia8on, maximum and mínimum from ver8cal los horizontal cross-sec8on.
When the materials are compared to each other at the end of the test, 120,000 cycles, Ceramic
Crown showed the least amount of volumetric loss (-18.76 ± 15.68 µm), followed by the Lava
Ul0mate material (-108.55 ± 11.90 µm) and finally, the material showing the most amount of
wear is the VarseoSmile Crown Plus (-166.33 ± 37.33 µm) (Table 42).
Figure 69: : Independent samples Kruskall-Wallis Test
The Non-parametric Kruskal-Wallis Test showed that there was significant difference between
the different tested materials. (p=0.001) for the independent samples analysis as seen in Figure
69.

103
For the pairwise comparison, the results
showed that there was no significant between
the Lava Ul0mate and the Ceramic Crown
(p=0.065), neither between the VarseoSmile
Crown Plus and the Lava Ul0mate (p=0.085) and it appeared to be a sta0s0cal difference
between the VarseoSmile Crown Plus and the Ceramic Crown (P=0.000) as seen in Figure 70,
Table 43.
Figure 70: Overall pairwise comparison between materials
Table 43: : Overall pairwise comparison between materials

104
3.9.3. Ver0cal loss of the antagonist between different materials Ver0cal crosssec0on
Table 44: Mean, Standard devia8on, maximum and mínimum from ver8cal los horizontal cross-sec8on
When the materials are compared to each other at the end of the test, 120,000 cycles, Ceramic
Crown showed the least amount of volumetric loss (-21.18 ± 11.30 µm), followed by the Lava
Ul0mate material (-107.77 ± 12.65 µm) and finally, the material showing the most amount of
wear is the VarseoSmile Crown Plus (-171.09 ± 34.35 µm) Table 44.
Figure 71: Independent samples Kruskall-Wallis Test
The Non-parametric Kruskal-Wallis Test showed that there was significant difference between
the different tested materials. (p=0.001) for the independent samples analysis as seen in Figure
71.

105
For the pairwise comparison, the results
showed that there was no significant
between the Lava Ul0mate and the Ceramic
Crown (p=0.065), neither between the
VarseoSmile Crown Plus and the Lava
Ul0mate (p=0.085) and it appeared to be a sta0s0cal difference between the VarseoSmile
Crown Plus and the Ceramic Crown (P=0.000) as seen in (Figure 72) (Table 45).
Figure 72: Overall pairwise comparison between materials
Table 45: Overall pairwise comparison between materials

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Chapter 4: Discussion
The objec0ve of this study was to assess the wear resistance and behavior of different 3D
printed materials for defini0ve restora0ons using an in vitro method. The final data indicates
that the wear resistance of the materials vary, thus rejec0ng the null hypotheses.
The second objec0ve of this study was to assess the effect of wear through different cycles of
different 3D printed materials for defini0ve restora0ons. The final data indicates that there is a
difference between the different number of cycles, thus rejec0ng the second null hypotheses
as well.
4.1. Materials
Our results show that there is a sta0s0cal difference when the Ceramic Crown is compared to
the VarseoSmile Crown Plus and the milled material Lava Ul0mate regarding the volumetric loss
aher a total of 120,000 cycles. However, there seems to be no sta0s0cal difference between
the Lava Ul0mate and the VarseoSmile Crown Plus. Thus, we can par0ally reject the null
hypothesis as only one of the printed materials behaved differently than the milled Lava
Ul0mate.
In general, the results show a that the material with the least amount of wear, more specifically,
volumetric loss, is the Ceramic Crown, then followed by the Lava Ul0mate and the material with
the most volumetric loss aher the tes0ng was the VarseoSmile Crown Plus.
The physical and mechanical proper0es of the materials will have a direct influence on their
behavior in the oral environment and will have an impact on survival and success rates of the
restora0ons.

107
Mechanical proper0es of dental polymers, specifically dental composites, are very dependent
on the polymers proper0es, fillers and coupling agents, thus it is a mul0variable. (69) In terms of
fillers, it has been reported that the wear resistance of dental composites in general is best in
materials with higher filler content and small par0cle size. (139) While other research has
described that the bigger the par0cle sizes, the more resistance to wear the material will have.
(114) In our study, Lava Ul0mate was the material with higher load of filler and smaller par0cle
size, however, it showed more wear compared to the 3D printed composite material Ceramic
Crown, less wear than VarseoSmile Crown Plus.
Smooth par0cles will also be considered becer for wear and antagonist wear, as they will be
less aggressive to the antagonist material once exposed or released to the interface and
actua0ng as a three body wear (140) In the current, wear of the antagonist was also addressed
by 3D op0cally scanning the surface along the different cycles. Sta0s0cal analysis shows no
difference between the different materials and antagonist ceramic wear.
Also, silaniza0on of the fillers is of key importance as it will be able to create a bond with the
monomers and have a becer distribu0on of the forces and less degrada0on over 0me.
In general considera0ons, the wear of dental composites is based on fa0gue wear and adhesive
wear. (114) In the current study, the only material sta0ng the saliniza0on of the coupling agents
was VarseoSmile Crown Plus, without any specifica0on of the silane itself. Lava Ul0mate
consists on silicon oxide fillers and zirconium fillers, thus, it can be understood that for the
zirconium par0cles, other coupling agents other than the silane are needed in this case. As for
the Ceramic Crown Group, neither the composi0on of the fillers nor the use of a silane agent
is disclosed.

108
In general, it is expected an increased amount of wear at the ini0al stages of the process that,
while the cycles augment, the process is becomes slower. (110) When all the materials are
compared together, it can be seen a progressive wear, with only sta0s0cal significance between
the ini0al and the final evalua0on. Thus, following a different pacern than what would be
expected.
4.1.1. LAVA ULTIMATE
Lava Ul0mate is a resin-based composite that is used for indirect restora0ons and
manufactured using subtrac0ve methods. This material has been previously classified as a
polymer matrix infiltrated with high content of ceramic fillers, considering it a “hybrid”
material or even resin-matrix ceramics. (141) However, when we look at the material’s content,
we can see that it consists on a polymer based resin composite as it is a nano filled organic resin
matrix that consists on TEGDMA, bisGMA, bisEMA and UDMA monomers. (61, 62) This material
has filler par0cles that are consist of a colloidal silica and zirconium oxide spherical par0cles
presented in an agglomerated that range the size of around one micron together with a
nonagglomerated form consis0ng of an 80 % wt. and 65 % volume overall the material. What
makes this material special in comparison to the direct composite that is cured intraorally with
light or dual cure ac0va0on is that the material is manufactured outside the pa0ent’s mouth
allowing for a high pressure and high temperature during polymeriza0on, allowing for higher
rates of degree of conversion of the polymer, leading to what has been reported to higher
mechanical proper0es and wear resistance. (90) Lava Ul0mate has been reported to have a
hardness of 121.70 VHN and a modulus of elas0city of 17.25 Gpa. (63)

109
Lava Ul0mate was the second most worn material. This material did not show any
complica0ons when polishing nor any changes in color. There appeared to be less plas0c
deforma0on on the borders of the tested area when compared to the other two 3D printed
materials, Ceramic Crown and VarseoSmile Crown Plus. When the profilometry was addressed,
less plas0c deforma0on was seen on the margins of the worn area compared to the other two
tested materials. Higher degree of polymeriza0on and higher filler loads of this material due to
the manufacturing methods of this material can achieve a more rigid material, with less plas0c
deforma0on as seen in Figure 73. (90) In this figure it can be perceived how there’s a sharp
transi0on between the flat surface and the worn area of the sample with minimal to no plas0c
deforma0on.
Figure 73: Horizontal profilometry of Lava Ul8mate ajer 120,000 cycles
As for the filler content, this composite can be considered a nanocomposite. Nanocomposites
have shown higher sorp0on and solubility compared to hybrid composites, which may
influence the clinical performance of the material. Wear capabili0es of nanocomposites have

110
been reported to be similar to hybrid resin composites.(142) The current research compared a
nanocomposite to 2 different 3D printed composite based materials, showing no difference to
one of the materials and underperforming when compared to Ceramic Crown which has
average par0cle sizes of 1.2 µm (Dr Sillas Duarte personal communica0on).
As for the wear depending on the number of cycles, Lava Ul0mate shows a con0nuous
accumula0on of wear through the test. Which could be related to the manufacturing method
of the material, with no flaws and a monolithic composi0on.
4.1.2. VARSEOSMILE CROWN PLUS
VarseoSmile Crown Plus is a 3D printable polymer-based resin considered as a material for
defini0ve restora0ons such as par0al restora0ons like onlays and inlays and even the fabrica0on
of crowns. This material has consisted of a composite based on silanized dental glass with
par0cle sizes of 0.7 µm that are embedded at a 30 to 50 % by weight in a matrix that consists
of 4-0- isopropylidiphenol, ethoxylated and 2-methylprop-2enoic acid. This material has been
reported by previous studies to have a hardness of 45.78 VHN (63) and a modulus of elas0city
of 6.79 Gpa.
This material has shown the most amount of wear of all the materials tested. The material was
easy to manufacture and easy to polish. The surface of the material aher the wear test was
smooth and with no changes in color. An interes0ng aspect to consider about this material is
that the borders of the worn area appeared to have had a plas0c deforma0on, with the material
higher than at baseline as seen in Figure 74, this may be due to the reduced amount of
polymeriza0on of the composite and the reduced amount of fillers. In this case, it is disclosed
by the manufacturer that the photo ini0ator used is TPO. TPO has a peak absorbance at around

111
400 nm which is ideal for 3D prin0ng as the used printer have a 405 nm light. It has been
demonstrated in some cases that the composites that used TPO can achieve a higher hardness
value. (89) In this study the harness value of Lava Ul0mate was higher, however the
manufacturing process is different as it is processed in high temperature and high pressure.
Which can explain a higher fa0gue accumula0on of the material that ends up in increased
amount of wear.
Figure 74: Horizontal profilometry of VarseoSmile Crown Plus ajer 120,000 cycles.
One considera0on about the VarseoSmile Crown Plus material is the wide range that the
manufacturer states as filler content (30 to 50 % by weight). It has been addressed in previous
studies the influence of filler content and the wear resistance of materials. In dental composites
it has been seen that there’s a sta0s0cal difference when the filler load drops under 48% by
weight, increasing the amount of wear significantly with lower filler amounts. (143) This material
shows a wide range of filler content, which makes it highly inconsistent and leading to amounts

112
that are under the required filler load threshold for a good performance. In addi0on, the
flowability of this material can lead to uneven dispersion of the filler par0cles in the resin while
it is prin0ng as the heavy filler par0cles will be falling to the bocom of the vat through the
process, which could lead to a an inhomogeneous manufactured restora0on. (105) Although
there seems to be no sta0s0cal differences between the chambers as seen in Error! Reference s
ource not found., there is some inconsistency of wear amounts in the material itself, which
could be acributed to this fact.
When the effect of cycles is evaluated for VarseoSmile, there seems to be a fast wear at the
beginning, with a decreased amount of wear in the middle of the tes0ng and an increased
amount of wear as seen on Figure 54. This does follow the pacern which there is an increased
amount of wear at the ini0al stages, (110) however, we believe that the mechanical fa0gue of
the material during the cycles in the middle of the test end up debilita0ng the material and
increasing the wear speed aher certain amount of cycles.
4.1.3. CERACMIC CROWN
Ceramic Crown is a 3D printable polymer-based resin considered as a material for defini0ve
restora0on, cleared for veneers, par0al and full crowns. The material consists of a mix of
methacrylic acid esters, photo ini0ators, proprietary pigment, and addi0ve package and a 50
% inorganic ceramic content by weight and an average par0cle size of 1.2 µm (Dr Sillas Duarte
personal communica0on). Not much is disclosed of the content of the material at this point as
it is a recently released product to the market. The manufacturer claims a flexural modulus of
7.5 GPa and a flexural strength of 150 MPa.

113
Ceramic crown has shown the least amount of wear of all the tested materials. Thus, the
composi0on of the material has shown to have an influence in the mechanical proper0es of
the material. This material has shown some complica0ons during the manufacturing process.
While Lava Ul0mate showed an easy polishable surface, Ceramic Crown was much more
complex and required much more 0me to achieve a polished shiny surface, which never
achieved a polished surface as the Lava Ul0mate or the VarseoSmile when compared visually.
An aspect that could also be taken into considera0on is the white mac finish of the material
aher the post processing, including cleaning and curing Figure 21. The opaque white finish
could be easily removed aher the polishing was performed; however, it has been seen that
aher the wear test, the area of contact with the antagonist had again the white appearance,
with a clear change of color of the surface of the material aher the wear tests were conducted.
As the light goes through different materials, it will change in direc0on depending on the
refrac0ve index of the materials(144). The change in color to a white appearance of the surface
can be related to the roughness of the surface, exposure of fillers and reflec0on of light,
breaking of the union between the filler par0cles and the resin matrix, leaving a gap which
could influence in the refrac0on of the light. It is not expected from materials to change their
op0cal proper0es when in use in pa0ents, thus, more research should be done to understand
what is the process that creates the change in color/surface for this material before it is used
in defini0ve restora0ons.
Some studies have reported that the macro filled composites have a higher wear coefficient
due to the lack of distribu0on of the forces in the material. (126) Other studies have shown that
the bigger the par0cle size, the becer it will behave as more influence of the physical proper0es
of the composite will be more related to the filler composi0on. (114) In this case the material

114
Ceramic Crown showed the highest wear resistance of all the tested materials and the one with
the bigger par0cle sizes.
In addi0on, the profilometry shows that the material has a rougher surface aher the wear
simula0on when compared to the other two materials tested as seen in Figure 75 and, again
shows a plas0c deforma0on of the material at the borders of the worn area, which we acribute
to a lower degree of conversion of the polymers.
Figure 75: Horizontal profilometry of Ceramic Crown ajer 120,000 cycles.
In the case of Ceramic Crown, the evalua0on of the effect of the cycles cannot be performed
as the data is inconsistent with the obtained results due to the scanning methods used as it will
be described further into the discussion.

115
4.1.4. EMPRESS CAD
Empress CAD is a leucite-reinforced glass ceramic block available for subtrac0ve manufacturing
using CAD / CAM technology. This is a material that has been recommended for applica0ons
like anterior crowns and veneers, posterior inlays and onlays. Empress CAD, which has a
reported hardness of 519 VHN (145) and an elas0c modulus of 58.4 Gpa (146) and a flexural
strength of 185 Mpa.
Previous studies have reported that dental ceramics are less suscep0ble to wear when
they are compared to dental composites based on polymers. (102) This research project has
focused on the wear of the composite based materials for defini0ve restora0ons against the
Empress CAD, thus wear of all the 3 materials was expected. Aher 120,000 cycles it could be
seen that all composites presented wear against the ceramic material, however they behaved
in different ways, while the leucite-reinforced glass ceramic showed a similar wear through all
the materials tested. It is important to evaluate the wear on the antagonists as well as it is part
of the whole wear system. (147)
One of the main factors about dental ceramics is that they can become very aggressive to the
natural teeth. And one way to avoid it is by polishing or glazing the surface of the ceramic. (140)
In this case, to standardize, all the antagonists were polished. The comparison of wear of the
antagonists lets us see how the standardiza0on was successful, with no difference between
materials.
As it has been reported that the use of natural enamel or hydroxyapa0te is a complex method
and can create inconsistency as the natural enamel has a lot of variability, different materials

116
have been used for in vitro simula0on. It has been reported that the material that behaved
close to enamel was the leucite reinforced ceramic, Empress Press. enamel. (136) In this study
we decided to use Empress CAD as it is easier to standardize the manufacturing process by
simply milling mul0ple 0mes the same files, allowing us to be consistent with the antagonists
used. Final polishing was performed as well to achieve a glossy surface. Each sample had its
own antagonist, and no antagonist was reused during this project.
4.1.5. Comparison to other materials
Similar wear simula0on with the Ivoclar method have tested different direct composite
materials against the ceramic antagonists, showing maximum ver0cal loss aher 120,000 cycles
for Dyract AP a mean of -338.1 µm, for Z250 a mean maximum ver0cal loss of -307.1 µm and
for Tetric Ceram a mean maximum ver0cal loss of 329.6 µm.(136) In our study, the average
maximum ver0cal loss recorded aher 120,000 cycles with the profilometer was of -107.77 µm
for the Lava Ul0mate material, -171.09 µm for the VarseoSmile Crown Plus and -21.18 µm for
the Ceramic Crown material. The differences could be also related to the fact that the Ivoclar
method involves thermocycling as well, which we did not include in our study. Also, the
polymeriza0on from the post-processing is expected to be becer than the direct light
polymeriza0on of the direct composites.
120,000 cycles can be related to 0.5 years of clinical wear.(127) It has also been reported that
for natural enamel in normal condi0ons it is expected wear of 20 µm to 30 µm in posterior
teeth.(118) Then we would expect a 10 µm to 15 µm of wear in half a year for natural den00on.
If we put these values into comparison with the obtained simula0on results, Ceramic Crown
would be the material with the closest mean wear to that of natural den00on (-21.18 µm).

117
However, the invitro wear simula0on has been reported to have low to moderate correla0on
with in vivo wear.(123)
When enamel is tested against the leucite ceramics, a volumetric loss of -2.042 mm3 has been
reported.(148) In our study, the material that showed the most volumetric loss is the Varseo
Smile Crown Plus with a total volume loss of -0.1323 mm3
. This difference could be related to
the difference of shape or even the difference of the stroke length, which for the reported
enamel was of 2mm while in our study it was of 0.7mm.
A wear simula0on with a ceramic antagonist, CeramTec, for 120,000 cycles and a load of 50N
comparing different composite based materials and ceramics, showed the least amount of
wear for e.max CAD, with a ver0cal loss of 132.2 µm and for Lava Ul0mate a total wear of -176.3
µm.(149) The results obtained for Lava ul0mate in our studies are very similar to the reported
values of wear, -171.09 µm.
4.2. Ver-cal loss – volumetric loss difference.
Volumetric loss is a way to measure the amount of wear of the materials as it is the volumetric
loss. It has been reported that both measurements have a high correla0on to each other and
thus, it would be unnecessary to measure both wear parameters while tes0ng the samples. (127)
In this case, more differences have been seen when the ver0cal loss was evaluated for the
different materials. It is in this case that we can see sta0s0cal differences between the different
between all the materials, while in the same situa0on using volumetric loss, we can only
appreciate sta0s0cal significance of Ceramic Crown compared to VarseoSmile Crown Plus and
to Lava Ul0mate.

118
While mechanical methods to measure the wear have shown increased values when compared
to op0cal sensors when volumetric loss is calculated, while if ver0cal loss is evaluated, the
op0cal scanners show consistent higher values compared to the mechanical ones. (127) There
are also studies sta0ng that there is a difference between the different measurements,
considering volumetric loss the most important as it looks at the whole picture of what has
been lost under wear tes0ng. Ver0cal loss can induce some confusion as it may depend on
which are it is exactly measure, inclina0on and it depends on different parameters. (147)
This could be an explana0on to the fact that the ver0cal loss showed more significance when
compared to the volumetric loss in general in this study.
4.3.Quan-fica-on
It has been reported that laser scanner cannot be used to evaluate ceramic or composites as
the laser will penetrate the material and will create wrong readings during the process, thus
replicas or powdering is needed if that method is preferred.(126)
As for the FRT MicroProf, an op0cal scanner, is an excellent tool to quan0fy wear, however it is
a technique that it cannot be considered for rou0ne as it is very 0me consuming and very
limited to certain depths such as 300 µm. (127) A mechanical profilometer may be an alterna0ve
method that has shown some discrepancies due to the distor0on of the needle while scanning,
especially in composite materials it has been shown to report higher wear than op0cal sensors.
(127)One of the advantages of using an op0cal scanner to evaluate the surface of the materials
is that the data will be acquired with no interference of any material into the surface of the
material, thus avoiding any interac0on, especially if applied in between the test and not only in
the end of the test. (127)

119
The intraoral scanner used for the quan0fica0on of the wear in this study was the Medit I700,
an op0cal intraoral scanner that has reported an accuracy of 10.9µm ± 0.98µm. The results
obtained show that there is a discrepancy between the obtained results and reality, especially
for the Ceramic Crown material. While the intraoral scans were repor0ng posi0ve wear,
meaning that the material grew instead of having a loss of material clearly shows that the data
was not accurate. Profilometry was used to check if there was material loss in that area. All the
obtained results seem to be an error from both the accuracy of the scanner itself and the nature
of the scanned material and the technology selected for the scanning as the profilometry shows
ranges of wear from -25 µm to -15 µm. The scans show a generalized material displacement of
the material in all the samples while all the profilometry shows a worn surface in all the
samples. Another way to explain the obtained results is that the op0cal scanner had an issue
in differen0a0ng the different surfaces with different polishing aher the wear and the
difference in color, especially in the ceramic crown group. The worn area presented a mate
white aspect that could influence the way the light projected from the scanner was reflected
in comparison to the surrounded polished surface. It has already been reported that different
materials and different surface finishing will have an influence on the scanning, especially when
the material is translucent. (29) It can clearly be seen that op0cal scanner, in this case based on
triangula0on technology may not be used for precision scanning tooth colored materials other
methods should be evaluated to maintain the same workflow and at the same 0me achieve
adequate precision for the scans. The use of the profilometer in the steps in between could be
an interes0ng op0on as it allows for precise scanning of the samples in a nondestruc0ve way
with no need to apply any powder or material on the surface.

120
4.4. Method
Other methods for wear analysis have been applied in research like the OHSU method, that
relies on two disks sliding on to each other, or the Zurich method, which uses natural enamel
as an antagonist and does 1,200,000 cycles. In this project, a simple and easy to reproduce
method, the Ivoclar method was used as a reference. While the IVOCLAR methods has shown
to be one with the least amount of varia0on. (126)
An interchangeable device was designed to be able to access the samples without the need to
take impressions of the materials and keeping the same posi0on of the samples aher the
scanning was performed. Most of the studies focus on the wear aher all the cycles have been
completed and thus leaving behind some important informa0on on how the wear is happening
through the process. In this case, the measurements were made directly on the samples thanks
to the interchangeable device with no need of powdering or making the material touch any
silicon or impression material that could affect or intervene in the wear process of the samples.
Another interes0ng aspect is the medium used for the study. Some ar0cles have described the
use of ar0ficial saliva to mimic the intraoral condi0ons. This is a process that can be complex as
it is much more complex than it seems trying to mimic intraoral environment in an in vitro
study, thus the use of dis0lled water has been proposed to maintain redundancy during the
whole process.(150) In this project, the medium that was used was dis0lled water.

121
4.5.Other considera-ons
Other aspects that need to be taken into considera0on are the use of two different 3D printers
for the manufacturing of the different materials. Both printers that were used relied on the
same DLP technology by the same manufacturer. Also, the post processing of the VarseoSmile
Crown Plus was using a different post processing protocol, which may have had an influence on
the final proper0es of the materials even though all the post process was performed under the
manufacturer’s recommenda0ons for both materials.

122
Chapter 5: Conclusions
- In-vitro wear of milled and printed defini0ve CAD/CAM materials is material dependent and
increases with increasing number of wear cycles. The material Ceramic Crown had the highest
wear resistance compared to VarseoSmile Crown Plus and Lava Ul0mate.
- Composi0on, filler characteris0cs and mechanical proper0es need to be further assessed to
be able to improve and define what are the real limits to use the tested materials while there
is a lack of clinical studies.
- The interchangeable method is an adequate method to facilitate the evalua0on of samples at
different 0mepoints during the tes0ng of wear.
- Different data acquisi0on devices other than the intraoral op0cal scanners based on
triangula0on should be used to avoid any interference with tooth-colored materials.

123
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Abstract (if available)

Abstract Purpose: To evaluate the two-body wear of three CAD / CAM resin based permanent dental materials (subtractive: Lava Ultimate; additive: VarseoSmile Crown Plus, Ceramic Crown) against a ceramic material (Empress CAD) using a two-axis chewing simulator.

Material and Methods: 24 samples were fabricated with 8 samples per group for the 3 different materials. The samples were fabricated and standardized by polishing the top surface. Then, they were attached to an interchangeable mounting system to ease the positioning of the samples during surface analysis. Dual-axis chewing simulator (CS-8, SD Mechatronic, Feldkirchen-Westerham, Germany) was used for 120,000 cycles, applying 5kg on each bar with a 0.7mm sliding movement at a frequency of 1.6Hz in distilled water. The samples and the antagonists were analyzed with a surface optical scanner to evaluate volumetric loss and maximum wear depth at different stages of the process. Additionally, profilometry was performed on the samples after 120,000 cycles.

Data was analyzed using nonparametric tests: Kruskal-Wallis Test (α=0.05) with Bonferroni post-hoc test.

Results: Volumetric loss and vertical loss differed between materials (Ceramic Crown < Lava Ultimate < VarseoSmile Crown Plus). A statistically significant difference between Ceramic Crown and the other two materials was shown. The number of cycles also showed an increase of wear as the number of cycles increased.

Conclusions: The wear of definitive milled and printed CAD/CAM materials is material and wear cycle dependent. The material with the larger filler particles showed less wear than the other two materials. Wear increases with increasing numbers of cycles.

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Asset Metadata

Creator Llena Prats, Jordi (author)

Core Title Wear resistance analysis of additively manufactured materials for permanent restorations.

School School of Dentistry

Degree Master of Science

Degree Program Biomaterials and Digital Dentistry

Degree Conferral Date 2023-12

Publication Date 11/21/2023

Defense Date 11/09/2023

Publisher Los Angeles, California (original), University of Southern California (original), University of Southern California. Libraries (digital)

Tag additive manufacturing,chewing simulator,digital dentistry,OAI-PMH Harvest,permanent restorations,subtractive manufacturing,wear

Format theses (aat)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Phark, Jin-Ho (committee chair), Alsaleh, Sarah (committee member), Duarte, Sillas Jr. (committee member)

Creator Email llenapra@usc.edu,toti.llena@me.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-oUC113777751

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Format theses (aat)

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