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Influence of a novel self-etching primer on bond-strength to glass-ceramics and wettability of glass-ceramics

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Influence of a novel self-etching primer on bond-strength to glass-ceramics and wettability of glass-ceramics

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Influence of a Novel Self-Etching Primer on Bond-Strength to Glass-Ceramics and
Wettability of Glass-Ceramics
In Partial Fulfillment
of the Requirements for the Degree of
Master of Science in Craniofacial Biology
University of Southern California
May 2017
By: Haifa A. Alsobiyl, BDS

Advisor: Dr. Jin-Ho Phark

2
TABLE OF CONTENTS
Table of contents ..........................................................................................................................................2
Dedication .....................................................................................................................................................3
Acknowledgements ......................................................................................................................................4
List of figures and tables .............................................................................................................................5
Abbreviations ...............................................................................................................................................7
Abstract……. ................................................................................................................................................8
1. Introduction .......................................................................................................................................10
1.1. Silica based glass-ceramics ...............................................................................................................10
1.1.1.Leucite reinforced glass-ceramic .....................................................................................................11
1.1.2.Lithium disilicate reinforced glass-ceramic ....................................................................................13
1.2. Bonding to silica based glass-ceramics ............................................................................................15
1.2.1.Conventional surface treatment ......................................................................................................15
1.2.2.Alternative surface treatment ..........................................................................................................17
2. Objectives ...........................................................................................................................................20
3. Materials and methods .....................................................................................................................21
3.1. Study design .......................................................................................................................................21
3.2. Bond strength testing ........................................................................................................................21
3.2.1.Specimen preparation .......................................................................................................................21
3.2.2.Surface treatment ..............................................................................................................................24
3.2.3.Adhesive bonding procedures ..........................................................................................................25
3.2.4.Micro-tensile bond strength (µTBS) testing ...................................................................................25
3.3. Wettability .........................................................................................................................................26
3.3.1.Wettability after different surface treatments ...............................................................................26
3.3.2.Wettability of different agents on polished glass-ceramics ...........................................................27
3.3.3.Statistical analysis .............................................................................................................................28
4. Results ................................................................................................................................................30
4.1. Micro-tensile bond strength (µTBS) ................................................................................................30
4.2. Contact angle of water after different surface treatments ............................................................32
4.3. Contact angle of different agents on polished glass-ceramics .......................................................36
4.4. Scanning electron microscope micrographs ...................................................................................42
5. Discussion ...........................................................................................................................................43
6. Conclusions ........................................................................................................................................49
7. References ..........................................................................................................................................50

3
DEDICATION
To my parents, Faiza and Abdullah, for their unconditional and unwavering love and support.
To my sisters and brother, for being my best friends.
To my mentor, Dr. Yousra Al-Jazairy, for being an inspiration.
To my friends and family who have always believed in me.

4
ACKNOWLEDGEMENTS
I would like to thank the committee members who were more than generous with their time and
expertise. A special thanks to Dr. Jin-Ho Phark, my mentor, and the committee chairman for his
countless hours of reflecting, reading, and encouragement throughout this entire process.
I would also like to acknowledge and thank my program directors, and my committee members
Dr. Sillas Duarte, Dr. Michael Paine and Dr. Neimar Sartori for providing their expertise and
guidance throughout the program.
I would like to acknowledge and thank the advanced operative program faculty and staff,
specially Mrs. Karen Guillen, for providing any assistance requested.
Finally, I would like to thank my co-residents for their constant words of encouragement as we
go through this process together.
This study was supported by the Advanced Program in Operative and Adhesive Dentistry.
5
LIST OF FIGURES AND TABLES
FIGURES
Figure 1: Mean micro-tensile bond strength (µTBS) values in MPa for groups 1-10 after 24 hours
and 6 months ......................................................................................................................... 31
Figure 2: Mean contact angle values for leucite reinforced glass-ceramic after different surface
treatments at 0, 20, 40, 60 and 120 s. ................................................................................... 33
Figure 3: Contact angle of distilled water at 0 s on polished (600 grit) leucite reinforced glass-
ceramic (IPS Empress CAD) after different surface treatments: a) no surface treatment; b) HF
acid for 60 s; c) HF acid for 60 s and silane for 60 s; d) MBEP agitated for 20 s, left for 40 s;
e) MBEP agitated for 20 s, left for 100 s. ............................................................................. 33
Figure 4: Mean contact angle values for lithium disilicate reinforced glass-ceramic after different
surface treatments at 0 s, 20 s, 40 s, 60 s and 120 s. ............................................................. 34
Figure 5: Contact angle of distilled water at 0 s on polished (600 grit) lithium disilicate reinforced
glass-ceramic (IPS e.max CAD) after different surface treatments: a) no surface treatment, b)
HF acid for 20 s, c) HF acid for 20 s and silane for 60 s, d) MBEP agitated for 20 s, left for
40 s, e) MBEP agitated for 20 s, left for 100 s. ..................................................................... 35
Figure 6: Mean contact angle values of different agents at 0, 20, 40, 60 and 120 s on 600 grit
polished leucite and lithium disilicate reinforced glass-ceramic surfaces: 1/6(W) – Water,
2/7(HF) – HF acid, 3/8(S) – Silane, 4/9(S2) – Silane after HF acid etching, 5/10(MBEP) –
MBEP. ................................................................................................................................... 37
Figure 7: Contact angle of different agent on leucite reinforced glass-ceramic .......................... 38
Figure 8: Contact angle of different agent on lithium disilicate reinforced glass-ceramic: ........ 39
Figure 9: Mean contact angle values of different agents at 0 s, 20 s, 40 s, 60 s and 120 s on leucite
reinforced glass-ceramic and lithium disilicate reinforced glass-ceramic 1200 grit polished
surfaces: 1/6(W) – Water, 2/7(HF) – HF acid, 3/8(S) – Silane, 4/9(S2) – Silane after HF acid
etching, 5/10(MBEP) – MBEP. ............................................................................................ 41
Figure 10: Scanning electron microscopy of intaglio surfaces of a) leucite reinforced glass-
ceramic after surface treatment of HF acid for 60 s; b) leucite reinforced glass-ceramic after
surface treatment of MBEP 20+40, c) leucite reinforced glass-ceramic after surface treatment
of MBEP 20+100, d)lithium disilicate reinforced glass-ceramic after surface treatment of HF
acid for 20 s; e) lithium disilicate reinforced glass-ceramic after surface treatment of MBEP
6
20+40; f) lithium disilicate reinforced glass-ceramic after surface treatment of MBEP
20+100. ................................................................................................................................. 42

TABLES
Table 1: Materials and agents used for surface treatment of glass-ceramics ............................... 22
Table 2: Firing parameters for IPS e.max crystallization for Programat CS3 Furnace ............... 23
Table 3: Experimental groups and surface treatment ................................................................... 24
Table 4: Experimental groups and contact angle agents .............................................................. 27
Table 5: Mean micro-tensile bond strength (µTBS) values and standard deviation (SD) in MPa,
number of pre-test failures (PTF) and total sticks ................................................................ 31
Table 6: Mean contact angle (°) for polished leucite reinforced glass-ceramic (IPS Empress CAD)
after different surface treatment at different time points ...................................................... 32
Table 7: Mean contact angle (°) for lithium disilicate reinforced glass-ceramic (IPS e.max CAD)
after different surface treatment ............................................................................................ 34
Table 8: Mean contact angle values (°) of different agents for leucite reinforced glass-ceramic
(IPS Empress CAD) and lithium disilicate reinforced glass-ceramic (IPS e.max CAD) ..... 36
Table 9: Mean contact angle of different agents for leucite reinforced glass-ceramic and
lithium disilicate reinforced glass-ceramic ........................................................................... 40

7
ABBREVIATIONS
3-MPS: 3-methacryloxypropyl-trimethoxysilane
µTBS: Micro-tensile bond strength
Bis-EMA: bisphenol A polyethethylene glycol diether dimethacrylate
DMA: Dimethylacetamide
HF: Hydrofluoric acid
LCRGC: Leucite reinforced glass-ceramic (IPS e.max CAD)
LDRGC: Lithium disilicate reinforced glass-ceramic (IPS Empress CAD)
RNC: Resin nanoceramic (Lava Ultimate)
SECP: Self-etching ceramic primer (Monobond Etch & Prime)
SEM: Scanning electron microscopy
TEGDMA: Triethylene glycol dimethacrylate
UDMA: Urethane dimethacrylate

8
ABSTRACT
Objective: The aim of this study is to evaluate the influence of a self-etching ceramic primer on
(1) micro-tensile bond strength (µTBS) to leucite reinforced glass-ceramic and to lithium disilicate
reinforced glass-ceramic and (2) to examine the wettability of these two glass-ceramics after
different surface treatments.

Materials and methods: CAD/CAM blocks made of leucite reinforced (IPS Empress CAD) and
lithium disilicate reinforced glass-ceramic (IPS e.max CAD) were cut into 6 mm thick sections
and polished with silicone carbide paper up to 600 grit. Resin nanoceramic blocks (Lava Ultimate)
of the same size were airborne-particle abraded for 20 s, cleaned and porcelain silane was applied
for 60 s. Leucite reinforced glass-ceramic specimens were assigned to the following groups: G1:
no surface treatment, G2: 60 s HF acid, no silane, G3: 60 s HF acid, silane, G4: self-etching
ceramic primer applied for 20 s and left for 40 s, G5: self-etching ceramic primer applied for 20 s
and left for 100 s. For lithium disilicate reinforced glass-ceramic surface treatment protocols were:
G6: no surface treatment, G7: 20 s HF, no silane, G8: 20 s HF, silane, G9: self-etching ceramic
primer applied for 20 s and left for 40 s, G10: self-etching ceramic primer applied 20 s and left for
100 s. The ceramic specimens were cemented to the resin nanoceramic blocks with a dual-cure
resin cement (RelyX Ultimate), then sectioned and subjected to µTBS testing using a universal
testing machine (Instron) after 24 h (non-aged) or 6 months (aged) of storage in distilled water.
Contact angle for distilled water was measured on both ceramics after different surface treatment.
Additionally, contact angles for different agents was measured on polished ceramic surfaces.
Ultra-structural analysis of the different surfaces was conducted with scanning-electron
microscopy. Statistical analysis of the data was performed using non-parametric (Kruskal-Wallis
and Mann-Whitney) tests after Bonferroni correction at α=0.001.

Results: For leucite reinforce glass-ceramic (groups 1-5), µTBS values ranged from 21.45 to 45.15
MPa for non-aged specimens and from 0 to 38.81 MPa for aged specimens. For lithium disilicate
reinforced glass-ceramic (groups 6-10), µTBS values ranged from 0 to 45.50 MPa for non-aged
specimens and from 0 to 32.10 MPa for aged specimens. Bond strength values were significantly
influenced by the factors material, surface treatment, and age (p=.000)
For leucite reinforced glass-ceramic, the highest contact angle values were observed for surfaces
treated with self-etching ceramic primer, while the lowest contact angle value was achieved by HF
9
acid and silane treated surface. For lithium disilicate reinforced glass-ceramic, the highest water
contact angle was recorded on surfaces treated with the self-etching ceramic primer for 20+40 s
and the lowest on surfaces treated with HF acid and silane.

Conclusion: Long term efficacy of self-etching ceramic primer is highly dependent on the
ceramics' composition and structural arrangement. Wettability of glass-ceramic surfaces is
impacted by different surface treatments and agents applied.
10
1. INTRODUCTION
With the increased demand for metal free restorations, many ceramic materials have been
introduced to the market. It is attributed to the ability of the ceramic to mimic the optical properties
of the dental substrate and create a highly esthetic restoration.
1
Advancements of adhesive bonding
techniques have led to an increase in fracture resistance of the tooth and the bonded ceramic
restoration; however, the variety of compositions, structures, and material properties can be
overwhelming. A new classification based on the chemical composition of dental ceramics was
developed. This classification includes three categories: silica based glass-ceramic, oxide based
ceramics, and resin-matrix ceramics. Silica based glass-ceramic consist of more than 15% of silica,
whereas, oxide-based ceramics are polycrystalline and have no glassy phase, or a content of less
than 15% silica in their composition.
2,3

1.1. SILICA BASED GLASS-CERAMICS
Silica based glass-ceramic best mimic the optical properties of enamel and dentin. They consist of
a highly-organized structure of atoms. The distances and angles between neighboring atoms are
both maintained constant throughout the 3D glassy network.
4
Glass-ceramic is derived from
naturally occurring feldspar minerals (K
2
O.Al
2
O
3
.6SiO
2
). These ceramics are generally weak due
to their sub-structural flaws.
5
When potassium based feldspar is melted and cooled fast, it forms
glass. When this glass is heated again it forms leucite.
6
Depending on the chemical composition,
phases, crystalline microstructure and production process, variable silica based glass-ceramic have
been introduced.
7
Multiple fillers were added to the silica backbone to reinforce them, hence to
improve their mechanical properties, and also to provide resistance to crack propagation e.g.
(leucite, lithium disilicate, fluoroapatite, fluormica, or alumina).
8

11
1.1.1. LEUCITE REINFORCED GLASS-CERAMIC
Leucite frit is a reaction product of mined minerals of potassium feldspar and glass, when subjected
to high fusing temperatures, which is then quenched rapidly and granulated.
9
The leucite based
frits were first used in 1960s as feldspathic veneering ceramic for various metal alloys.
9, 10
They
are produced by means of heat treatment of glass, K
2
O, Al
2
O
3
, and SiO
2
, together with other
components, and nucleating agents. Due to their high coefficient of thermal expansion, and ability
to mask the underlying substrate, they gained high popularity as a veneering material for metal
ceramic restorations.
10
Nowadays, with increased demand of highly esthetic restorations, leucite
crystals are used mainly as fillers in all ceramics restorations.
7
They were the first type of
reinforcing fillers introduced to glass-ceramics.
11
Leucite (K
2
O.Al
2
O
3
.4SiO
2
) is a potassium–
aluminum–silicate based reinforcing phase that can be added to glass-ceramics by various
methods. These methods include:
(1) Incongruent melting of potash feldspar, during which the raw feldspar is subjected to a heat
treatment for several hours at 1,200°C at which the leucite crystallization starts. The resultant
glass-ceramic obtained has around 40% volume tetragonal leucite.
Leucite crystals exist in two different phases, cubic and tetragonal. These crystalline structures
occur depending on the heat treatment temperature. Cubic to tetragonal leucite phase
transformation occurs at a temperature of 620°C. This phase transformation is associated with a
1.2% volumetric change, causing strain in the ceramic glassy matrix framework.
7
The tetragonal
leucite phase is essential in case of feldspathic veneering ceramic, to provide the necessary
coefficient of thermal expansion match between the veneering ceramic and the metal alloy. The
difference in coefficient of thermal expansion between the tetragonal leucite crystals phase and the
glassy matrix retain tangential compressive stresses around the crystals. These stresses are
12
accountable for strengthening mechanisms of the leucite veneering glass-ceramic.
12
However, the
cubic or high leucite phase is essential for improving mechanical properties of all ceramic leucite
based materials.
9

(2) Dispersion of synthetic leucite powder particles by mechanical mixing and precipitation in the
glassy matrix enhance the mechanical properties.
13,14
This mechanism is called “dispersion
strengthening”. In order to reinforce the glass, the leucite content must exceed 40 to 55%.
4

(3) Another approach of reinforcement is obtained by “Ceraming” or growing the filler particles
within the glassy matrix by modifying the glass composition. After special heat treatment,
precipitation and growth of leucite crystallites takes place from within the glass.
15
The nucleating
agent K
2
O then promotes a surface crystallization inward, leaving the inner bulk crystalline free.
7

Leucite reinforced glass-ceramics can be processed by sintering of powders, hot pressing, or
CAD/CAM milling.
7
Many contemporary leucite reinforced glass-ceramic products are available
nowadays to be used with CAD/CAM technology e.g. (Paradigm C, 3M ESPE, St. Paul, MN,
USA; ProCAD, Ivoclar Vivadent, Schaan, Liechtenstein; IPS Empress CAD, Ivoclar Vivadent,
Schaan, Liechtenstein) IPS Empress CAD (Table 1) is a leucite reinforced glass-ceramic of the
SiO
2
-Al
2
O
3
-K
2
O materials system. The leucite crystals (KAlSi
2
O
6
) are 1 – 5 µm in diameter and
occupy 35 – 45 % by volume. They are formed in a controlled nucleation and crystallization
process.
In general, ceramics with 22% leucite content presented higher fracture toughness and crack
deflection properties compared to those with a lower content
16
and with those of non-leucite
containing feldspathic glass-ceramics.
17
The resulting ceramic can therefore be called “leucite
reinforced glass-ceramic”.
4
The use of leucite as filler in leucite reinforced glass-ceramic can cause
13
the modification of the coefficient of thermal expansion, providing a refractive index that matches
the glassy matrix offering excellent esthetics. Furthermore, it increases fracture toughness and
flexural strength by means of crack deflection. The leucite content is highly affected by: multiple
firings, heat treatment, cooling rate, and long exposure to saliva. Extended glaze firing treatment
can significantly enhance the fracture strength and decrease the surface roughness, without the
alteration of the crystalline structure.
18
The grain size of leucite crystals and their distribution have
an impact on flexural strength and optical properties of leucite reinforce glass-ceramic. Finer, well
distributed leucite crystals of (1.2 µm
2
) have significantly higher biaxial flexural strengths than
leucite reinforced glass-ceramic with larger leucite crystals.
19

1.1.2. LITHIUM DISILICATE REINFORCED GLASS-CERAMIC
Lithium disilicate reinforced glass–ceramic (Li
2
Si
2
O
5
) was first developed by Stockey in 1959.
However, it was not until 1998 that it was introduced to the market in the form of a product called
IPS Empress 2 (Ivoclar Vivadent, Schaan, Liechtenstein).
20
The first generation of lithium
disilicate reinforced glass-ceramic contains 60% lithium disilicate crystals (5 - 6 µm in length and
1 µm in diameter) in addition to smaller secondary lithium orthophosphate crystals (0.1 to 0.3 µm).
The second generation of lithium disilicate reinforced glass-ceramic however contains 70 vol%
crystalline lithium oxide fillers added to the alumino-silicate glass. The production of these types
of ceramics is very complex. It involves a crystal phase formation or nucleation, followed by
crystal growth, leading to a highly packed and dense microstructure. In these processes, the
ceramic undergoes multiple dynamic cycles of controlled heat treatments.
21
The nucleation phase
takes place during a heat treatment cycle between 500 and 560 °C, in which the raw powders of
Li
2
O, SiO
2
, oxides, additives, and a nucleating agent (P
2
O
5
) are heated, leading to surface and
volume crystallization. With further increase of the temperature, lithium metasilicate crystals start
14
to grow and a lithium disilicate nanophase starts to agglomerate between 560 and 750 °C. At 850
°C lithium metasilicate will completely decompose and lithium disilicate crystals will optimally
grow in the glassy matrix to 3 - 6 µm long needle-like crystals. This transformation from lithium
metasilicate to a lithium disilicate glass-ceramic is associated with a very limited shrinkage of 0.2
– 0.3%.
7
Lithium disilicate reinforced glass-ceramic can be processed by hot pressing or injection
molding (IPS e.max Press, Ivoclar Vivadent, Schaan, Liechtenstein). Also, it is available to be
used with CAD/CAM technology, e.g. (IPS e.max CAD, Ivoclar Vivadent, Schaan, Liechtenstein)
(Table 1).
IPS e.max CAD blocks are in a partially crystalized stage, containing 40% by volume of lithium
metasilicate crystals embedded in a glassy matrix. After milling, the restoration must be subjected
to an additional heat treatment at 850 °C for optimal crystallization and transformation of lithium
metasilicate to lithium disilicate crystals.
22
In the partially crystalized stage IPS e.max CAD has a
flexural strength of 130 - 150 MPa. However, after the final crystallization process is completed
the strength of the material reaches up to 360-400 MPa.
23
The highest flexural strength values,
hardness and elastic modulus can be obtained, when lithium disilicate reinforced glass-ceramic is
subjected to an extended temperature range of (750 – 840 °C) and prolonged holding time (820–
840 °C) during the crystallization process.
22
Microstructural evaluation of the resultant lithium
disilicate reinforced glass-ceramic reveals large, fully grown, dense rod-like crystals. These
crystals are the main reason for the superior mechanical characteristics of lithium disilicate
reinforced glass-ceramic compared to those subjected to lower heat temperatures.
22

15
1.2. BONDING TO SILICA BASED GLASS-CERAMICS
Despite their inherent brittleness and low flexural strength, glass-ceramics gained wide popularity
after the advancement of adhesive bonding strategies. After final adhesive bonding with resin-
cement, the fracture resistance of the ceramic restoration and the substrate increases.
1, 24
Resin-
cements have multiple advantages over conventional luting cements when it comes to glass-
ceramic bonding. With resin-cements, the need of a retentive restoration is diminished, which
allows for preservation of tooth structure and consequently, the utilization of ultra-thin glass-
ceramics restorations.
25
Resin-cements show clinically accepted marginal fit and adaptation. Also,
resin-cements are available in various shades for optimizing the esthetics of the restoration. Due
to their unique microstructure, lithium disilicate reinforced glass-ceramics have significantly
higher flexural strength and fracture toughness compared to those of leucite reinforced glass-
ceramics.
26
Therefore, when the appropriate material thickness is utilized for lithium disilicate
reinforced glass-ceramics, clinicians might be able to either bond the restoration adhesively or
cement it conventionally.
27

1.2.1. CONVENTIONAL SURFACE TREATMENT
The intaglio surfaces of silica based glass-ceramics needs to be treated to achieve optimal adhesion
to resin based cements. This can be achieved by two mechanisms:
(1) Micromechanical interlocking after surface modification by mechanical or chemical means.
28

(2) Chemical bonding through application of coupling agents.
29

Surface modification of glass-ceramics is most commonly achieved by chemical alteration using
hydrofluoric acid (HF). The HF acid attacks the glassy matrix and exposes the crystalline structure,
16
creating a honeycomb-like surface roughness to aid eventually in micromechanical retention of
the resin-cements.
28

SiO
2
+ 4HF → SiF
4

(g) + 2H
2
O
SiO
2

+ 6HF → H
2
SiF
6

+ 2H
2
O
29

Beside it’s crucial role in adhesion, HF acid is a highly hazardous chemical to skin and soft tissues.
It is toxic, corrosive and highly reactive.
30
Moreover, despite being a weak acid, it’s toxicity arises
from the highly reactive fluoride ions. When HF acid comes in contact with living tissues, it can
cross lipid membranes rapidly and fluoride ions are released. These ions react with tissue’s calcium
and magnesium causing rapid tissue death and necrosis.
31
When HF acid comes in contact with
skin tissue, it causes a dehydration reaction, which subsequently can cause second- or third-degree
burns.
32
Hence, HF acid is not suitable for intra-oral use.
Chemical bond to glass-ceramics can be achieved using organosilanes. A silane is a bifunctional
molecule that creates covalent and hydrogen bond bridges between the siloxane network and the
silica glassy phase in ceramics. It copolymerizes with the organic matrix of the resin cement,
leading to a strong durable bond.
33

17
The application of a silane agent (3-methacryloxypropyl- trimethoxysilane [3-MPS]) increases the
surface energy and wettability of the HF etched surface, making it more receptive to the resin
cement.
28, 34
Silanes can be delivered in a pre-hydrolyzed 1-bottle system or in an unhydrolyzed 2-
bottle system, for which mixing of two components is required for activation. The first bottle
contains the unhydrolyzed silane and ethanol, while the second bottle contains acetic acid and
water. When mixed, the hydrolysis and activation of the silane functional group occurs.
Unhydrolyzed silanes have an advantage of a longer shelf-life than that of pre-hydrolyzed ones.
35

1.2.2. ALTERNATIVE SURFACE TREATMENT
Multiple agents were suggested to substitute HF, e.g. phosphoric acid, acidulated phosphate
fluoride, ammonium bifluoride, and titanium tetrafluoride.
Phosphoric acid (H
3

PO
4
) is mainly used to clean ceramic surfaces. When 40% phosphoric

acid is
applied for 60 s, it doesn’t modify the topography or morphology of the ceramic surface when
observed under Scanning Electron Microscopy (SEM).
36
However, 1.23%
Acidulated phosphate
fluoride (NaH
3
PO
4
F) can create etching pattern to some degree on glass-ceramic surfaces. When
applied for an extended period of time of 5-10 minutes followed by a silane agent, the bond
strength between feldspathic ceramic and resin-cement improves dramatically.
37,38
The only
downside of acidulated phosphate fluoride that it produces deposits on leucite reinforced glass-
ceramics surfaces.
37

Ammonium bifluoride (NH
4

HF
2
)
reacts with the silica constituent of glass, acting on the phase
boundaries only, creating an etching pattern that is similar to that of HF acid etching of lower
concentration or shorter duration.
39
However, surface treatment with titanium tetrafluoride (TiF
4
)
18
in various aqueous concentrations, failed to create stable adhesive bond between glass-ceramic
and resin-cement.
40

Besides, the previously mentioned chemical agents, other mechanical techniques have been
suggested to alter the ceramic surface, such as airborne particle abrasion, tribochemical silica
coating, and laser surface treatment. Airborne particle abrasion is carried out using 50-μm alumina
particles (Al
2
O
3
) under high pressure. These alumina particles modify the ceramic surface
mechanically, however some of these particles can embed in the surface loosely, which might
compromise the intaglio surface bond to resin-cement.
Tribochemical silica coating use silica coated alumina particles for surface modification, by
increasing the surface silica content and surface energy. The immediate silane application
afterward, forms covalent bonds between the silica-coated surface and the resin cement.
41

While some of the mentioned techniques might be suitable for oxide-based ceramics, most of these
techniques are not advocated for glass-ceramics.
42, 43
Due to the submicron cracks and defects that
might develop on the ceramic surfaces, which might eventually lead to slow crack growth, and
ultimately catastrophic fracture of the restoration.
5,44
Nevertheless, HF acid etching and
salinization remain the “gold standard” surface treatment for glass-ceramics, prior to resin-cement
adhesive bonding.
38, 39

Recently, a self-etching ceramic primer (Monobond Etch & Prime [MBEP], Ivoclar Vivadent,
Schaan, Liechtenstein) was introduced. Because it is mild and less toxic than HF acid, it might be
a suitable alternative to HF acid, especially in case of intraoral repair of ceramic restorations.
45

Furthermore, self-etching ceramic primer combines the chemical etching and the salinization
processes in one step, which makes it an attractive, less time-consuming substitute to the
19
conventional surface treatment.
46
It contains polyfluoride for the etching step and a
trimethoxypropyl methacrylate for silanization. The ammonium polyfluoride reacts with the
silicon in the glass-ceramic without the release of HF, due to the high chemical affinity between
silicone and fluoride. After rinsing and drying, a thin silane layer on a molecular scale remains at
the luting surface, which reacts through its methacrylate group with the resin-cement during
curing.
46

20
2. OBJECTIVES
Data about the effectiveness of a self-etching ceramic primer (Monobond Etch & Prime) when
applied to glass-ceramics are limited in the literature. Therefore, the aim of this study is to evaluate
the influence of a novel self-etching ceramic primer on micro-tensile bond-strength to leucite
reinforced glass-ceramic (IPS Empress CAD) and lithium disilicate reinforced glass-ceramic (IPS
e.max CAD).
The null hypotheses tested are (1) different surface treatment protocols have no significant effect
on the micro-tensile bond strength (µTBS) of resin cement to glass-ceramics tested. (2) Artificial
ageing has no significant influence on the durability of resin cement-glass-ceramic bonded
interfaces. (3) Contact Angle and wettability of ceramic surfaces are not affected by different
surface treatments.

21
3. MATERIALS AND METHODS
3.1. STUDY DESIGN
CAD/CAM blocks of leucite reinforced glass-ceramic and lithium disilicate reinforced glass-
ceramic received different surface treatment. They were then cemented to CAD/CAM resin
nanoceramic blocks of the same size that were air-abraded and salinized. For this purpose, a dual-
cure resin-cement was used. The bonded specimens were sectioned into micro-sticks, which were
subjected to micro-tensile bond strength (µTBS) testing using a universal testing machine after 24
hours or 6 months of storage in distilled water.
Water contact angle measurements were performed on glass-ceramic surfaces after receiving
different surface treatment, to evaluate the wettability and surface energy. Also, the contact angles
of the conditioning agents used for the surface treatment were measured to determine their
interaction with different glass-ceramic surfaces.

3.2. BOND STRENGTH TESTING
3.2.1. SPECIMEN PREPARATION
Both, leucite (IPS Empress CAD) and lithium disilicate (IPS e.max CAD) reinforced glass-ceramic
(Table 1) were sectioned into 14 x 14 x 6 mm blocks using a precision low-speed diamond saw
(IsoMet 1000, Buehler, Lake Bluff, IL, USA) under constant cooling with distilled water
(n=4/group). To remove any irregularities, scratches, and other surface defects the bonding surface
of each specimen was polished with abrasive silicon carbide paper (Carbimet Paper Strips,
Buehler, Lake Bluff, IL, USA) in ascending order (240, 320, 400 and 600 grit) under running
water.
22
Table 1: Materials and agents used for surface treatment of glass-ceramics

Material (Lot no.) Manufacturer Composition (%)
IPS Empress CAD
(T39745)
Ivoclar Vivadent,
Schaan,
Liechtenstein
SiO
2
(60.0–65.0), Al
2
O
3
(16.0–20.0), K
2
O (10.0–14.0), Na
2
O (3.5–6.5),
Other oxides (0.5–7.0), Pigments (0.2–1.0)
47

IPS e.max CAD
(R58825)
Ivoclar Vivadent,
Schaan,
Liechtenstein
SiO
2
(57.0–80.0), Li
2
O (11.0–19.0), K
2
O (0.0–13.0), P
2
O
5
(0.0–11.0), ZrO
2

(0.0–8.0), ZnO (0.0–8.0), Al
2
O
3
(0.0–5.0), MgO (0.0–5.0), Pigments (0.0–
8.0)
23

Lava Ultimate
(N687295),
3M ESPE, St.
Paul, MN, USA
Zirconia and silica nanoparticles (80 wt%), UDMA, Bis-EMA (20 wt%)
48.

Monobond Etch&
Prime (U20250)
Ivoclar Vivadent,
Schaan,
Liechtenstein
Ammonium polyfluoride, Trimethoxypropyl methacrylate, Alcohol, Water,
Green food colorant
46

IPS ceramic etching
gel (V00017)
Ivoclar Vivadent,
Schaan,
Liechtenstein
Hydrofluoric acid (5.5)
Porcelain Silane
(PK5114)
Premier Dental,
Plymouth
Meeting, PA,
USA
Ethyl alcohol (88), Isopropyl alcohol (4), Methanol (4.4)
RelyX Ultimate
(611351)
3M ESPE, St.
Paul, MN, USA
Base: Silane treated glass powder, 2-propenoic acid, 2-methyl-,1,1-[1-
(hydroxymethyl)-1, 2-ethanediyl] ester, Reaction products with 2-hydroxy-
1,3-propanediyl DMA and phosphorus oxide, TEGDMA, Silane treated
silica, Oxide glass chemicals, Sodium persulfate, Tert-butyl peroxy-3,5,5-
trimethylhexanoate, Copper (II) acetate monohydrate.
Catalyst: Silane treated glass powder, Substituted DMA, 1,12-dodecane
DMA, Silane treated silica, 1-benzyl-5-phenyl- barbic-acid, Calcium salt,
Sodium p-toluenesulfinate, 2-propenoic acid, 2-methyl-, [(3-metoxypropyl)
imino]di-2,1-ethanediyl ester, Calcium hydroxide, Titanium dioxide
49

UDMA: Urethane dimethacrylate; Bis-EMA: bisphenol A polyethethylene glycol diether dimethacrylate TEGDMA:
Triethylene glycol dimethacrylate; DMA: Dimethylacetamide.
23
Lithium disilicate reinforced glass-ceramic specimens (IPS e.max CAD) were crystalized
according to the manufacturer’s instructions (Programat CS3 Furnace, Ivoclar Vivadent, Schaan,
Liechtenstein) (Table 2). Prior to surface treatment and bonding, all specimens were cleaned by
immersion in ethanol (200 % Proof pure Ethanol, King of Prussia, PA, USA) in an ultrasonic bath
(Ultrasonic Cleaning Systems, Quantrex, Kearny, NJ, USA) for 10 mins.

Table 2: Firing parameters for IPS e.max crystallization for Programat CS3 Furnace

Stand-by temperature (B) 403/757 [°C/°F]
Closing time (S) 6:00 [min]
Heating rate (t1) 90/162 [°C/°F/min]
Firing temperature (T1) 820/1508 [°C/°F]
Holding time (H1) 0:10 [min]
Heating rate (t2) 30/54 [°C/°F/min]
Firing temperature (T2) 840/1544 [°C/°F]
Holding time (H2) 7:00 [min]
Vacuum (1-11)
Vacuum (1- 12)
550/820 [°C/°F]
1022/1508 [°C/°F]
Vacuum (2 - 21)
Vacuum (2 -22)
820/840 [°C/°F]
1508/1540 [°C/°F]
Long-term cooling (L) 700/1292 [°C/°F]
Cooling rate (t) 0 [°C/°F/min]
24
3.2.2. SURFACE TREATMENT
The ceramic specimens of each material were randomly assigned to 10 main experimental groups
according to the following surface treatment protocols (n=4/group) ( Table 3):
Table 3: Experimental groups and surface treatment

Group Ceramic Etching Silanization Aged Non-Aged
1
Leucite reinforced
glass-ceramic (IPS
Empress CAD)
none none 1(A) 1(NA)
2 HF acid for 60 s none 2(A) 2(NA)
3 HF acid for 60 s Silane 60 s 3(A) 3(NA)
4 MBEP applied for 20 s and left for 40 s 4(A) 4(NA)
5 MBEP applied for 20 s and left for 100 s 5(A) 5(NA)
6
Lithium disilicate
reinforced glass-
ceramic (IPS e.max
CAD)
none none 6(A) 6(NA)
7 HF acid for 20 s none 7(A) 7(NA)
8 HF acid for 20 s Silane 60 s 8(A) 8(NA)
9 MBEP applied for 20 s and left for 40 s 9(A) 9(NA)
10 MBEP applied for 20 s and left for 100 s 10(A) 10(NA)

Resin nanoceramic blocks (Lava Ultimate, 3M ESPE, St. Paul, MN, USA) were sectioned into 14
x 14 x 6 mm sections using a precision low-speed diamond saw (IsoMet 1000) under continuous
cooling with distilled water. The bonding surfaces were polished using abrasive silicon carbide
papers (Carbimet Paper Strips) in ascending order (240, 320, 400, 600 grit). These surfaces were
then treated with air-borne particle abrasion (Basic Classic, Renfert, Hilzingen, Germany) using
50-µm aluminum oxide particles (Cobra, Renfert, Hilzingen, Germany), cleaned with ethanol in
an ultrasonic bath (Ultrasonic Cleaning Systems) for 10 mins, dried, and silanated (Porcelain
Silane, Premier Dental, Plymouth Meeting, PA, USA) for 30 s in preparation for the bonding
procedures.

25
3.2.3. ADHESIVE BONDING PROCEDURES
After surface treatment, all ceramic blocks were cemented to the resin nanoceramic blocks with a
dual cure resin-cement (RelyX Ultimate, 3M ESPE, St. Paul, MN, USA) (Table 1). A custom-
made seating device was used to ensure uniform loading of all specimens with 1 kg load during
the bonding process. After 15 s, excess cement was cleaned with a micro-brush (Maxmicro Micro
Brush Applicators, Plasdent, Novi, MI, USA). Each specimen was light cured from each side for
20 s using a halogen-tungsten curing-unit (Elipar 2500, 3M ESPE, St. Paul, MN, USA) with a
radiant emittance of >1000 mW/cm
2
. Bonded specimens were left undisturbed for 6 minutes before
removal from the seating device and then stored in distilled water for 72 hours.

3.2.4. MICRO-TENSILE BOND STRENGTH (µTBS) TESTING
All bonded specimens were sectioned with a precision low-speed diamond saw (IsoMet 1000)
under distilled water coolant to obtain untrimmed sticks with a bonding surface of 0.64 ± 0.2 mm
2
.
Sticks obtained for each group were then divided into 2 subgroups: aged (A) and non-aged (NA).
Non-aged subgroups were tested after 24 hours of distilled water storage after sectioning, and aged
subgroups were tested after 6 months of storage. Long term water storage medium was distilled
water, storage temperature was maintained at 37°C.
Testing was carried out with a universal testing machine (Model 5965 Instron, Norwood, MA,
USA). Sticks were individually attached to a customized testing jig with a cyanoacrylate adhesive
(Zapit, Dental Ventures of America, Corona, CA, USA) and submitted to tensile forces until failure
at a crosshead speed of 0.5 mm/min. Type of failure was recorded as: adhesive, cohesive or mixed.
Pre-test failures (PTF) were recorded during cutting, testing, and long term water storage and were
given bond strength value of 0 MPa. These values were included in the statistical analysis.

26
3.3. WETTABILITY
3.3.1. WETTABILITY AFTER DIFFERENT SURFACE TREATMENTS
Both, leucite (IPS Empress CAD) and lithium disilicate (IPS e.max CAD) reinforced glass-ceramic
(Table 1) were sectioned into 14 x 14 x 4 mm sections using a precision low-speed diamond saw
(IsoMet 1000) under distilled water irrigation. Bonding surfaces of the specimens were polished
using 240, 320, 400, 600 grit silicon carbide abrasive papers (Carbimet Paper Strips) to remove
any irregularities, surface scratches and defects under running water. Lithium disilicate reinforced
glass-ceramic specimens were sintered according to the manufacturer’s instructions (Programat
CS3 Furnace; Table 2). All ceramic specimens were cleaned by the immersion in ethanol in an
ultrasonic bath for 10 mins and then were randomly assigned to 10 main experimental groups (n=4)
according to the surface treatment employed (Table 3). The sessile drop method was used to
measure the contact angle with an automated camera based goniometer (Ramé-Hart Model 290,
Netcong, NJ, USA). A 2 µl droplet of distilled water was dispensed from a micro syringe (diameter:
1.1 mm, NE42; Kruess, Hamburg, Germany) onto the ceramic specimen, which was placed on a
movable table. Dynamic contact angle measurement was performed at 0 s, 20 s, 40 s, 60 s, and
120 s with a dedicated software program (Drop Image Advanced Software for Windows, NJ,
USA).

27
3.3.2. WETTABILITY OF DIFFERENT AGENTS ON POLISHED GLASS-CERAMICS
Leucite reinforced and lithium disilicate reinforced glass-ceramic CAD/CAM blocks (IPS
Empress CAD and IPS e.max CAD) were sectioned to 4 mm thick sections, using a precision low-
speed diamond saw (IsoMet 1000) under distilled water coolant. Specimens bonding surfaces were
divided into 2 groups (n=4): group 1 was polished using 240, 320, 400, and 600 grit silicon carbide
abrasive papers (Carbimet Paper Strips) under running water. Group 2 was polished using 240,
320, 400, 600, and 1200 grit silicon carbide abrasive papers (Carbimet Paper Strips), followed by
using felt polishing pads with 0.05-µm diamond paste (Buehler, Lake Bluff, IL, USA).
Lithium disilicate reinforced glass specimens were then crystalized according to the
manufacturer’s instructions (Programat CS3 Furnace; Table 2). All ceramic specimens were
cleaned by immersion in 100% ethanol in an ultrasonic bath for 10 min, then each group was
assigned randomly to 10 experimental subgroups (n=4) according to contact angle agent (Table 4)
Table 4: Experimental groups and contact angle agents

Group Ceramic
Polished up to 600 grit Polished up to 1200 grit
Contact Angle Agent
1(W)
Leucite reinforced
glass-ceramic
(IPS Empress CAD)
Water
2(HF) HF acid
3(S) Silane
4(S2) Silane after HF acid for 60 s
5(MBEP) MBEP
6(W)
Lithium disilicate
reinforce glass-ceramic
(IPS e.max CAD)
Water
7(HF) HF acid
8(S) Silane
9(S2) Silane after HF acid for 60 s
10(MBEP) MBEP

28
3.3.3. STATISTICAL ANALYSIS
Bond strength data
Data for µTBS testing was entered into an Excel spreadsheet (MS Excel, Microsoft, Redmond,
WA, USA) in long format along with factors, such as ceramic material, surface treatment, and
artificial aging. Data was subsequently analyzed using a statistical software package (SPSS 19,
IBM, Armonk, NY, USA). Due to the non-normal distribution of the data (Kolmogorov-
Smirnov test p<0.05) and the heterogeneity of variances (Levene test p<0.05), non-parametric
tests were used. Kruskal-Wallis test was used to detect overall differences for the factors material
(leucite reinforced glass-ceramic vs lithium disilicate reinforced glass-ceramic), time (24 h vs 6
months), and surface treatment (for leucite reinforced glass-ceramic: none, 60 s HF, 60 s HF +
silane, MBEP 20+40 s, MBEP 20+100 s; for lithium disilicate reinforced glass-ceramic: none, 20
s HF, 20 s HF + silane, MBEP 20+40 s, MBEP 20+100 s). Group wise comparisons were
conducted separately for each material with Mann-Whitney test using Bonferroni correction due
to multiple comparison at α=0.001.

Contact angle data
Data for µTBS testing was entered into an Excel spreadsheet (MS Excel, Microsoft, Redmond,
WA, USA) in long format along with factors, such as ceramic material, surface treatment, and
artificial aging. Data was subsequently analyzed using a statistical software package (SPSS 19,
IBM, Armonk, NY, USA). Due to the non-normal distribution of the data (Kolmogorov-Smirnov
test p<0.05) and the heterogeneity of variances (Levene test p<0.05), non-parametric
test was used.
For analysis of the contact angle values using the drop of distilled water, Kruskal-Wallis test was
used to detect overall differences for the factors material (leucite reinforced glass-ceramic vs
29
lithium disilicate reinforced glass-ceramic), time (0 s, 20 s, 40 s, 60 s, 120 s), and surface
treatment (for leucite reinforced glass-ceramic: none, 60 s HF, 60 s HF + silane, MBEP 20+40
s, MBEP 20+100 s; for lithium disilicate reinforced glass-ceramic: none, 20 s HF, 20 s HF + silane,
MBEP 20+40 s, MBEP 20+100 s).
For analysis of the contact angle values using the drops of different surface treatment
agents, Kruskal-Wallis test was used to detect overall differences for the factors material (leucite
reinforced glass-ceramic vs lithium disilicate reinforced glass-ceramic), surface polish (600 grit vs
1,200 grit), time (0 s, 20 s, 40 s, 60 s, 120 s), and surface treatment agent (for leucite reinforced
glass-ceramic: none, 60 s HF, silane, 60 s HF + silane, MBEP 20+40 s; for lithium disilicate
reinforced glass-ceramic: none, 20 s HF, silane, 20 s HF + silane, MBEP 20+40 s).
Group wise comparisons were conducted separately for each material with Mann-Whitney
tests using Bonferroni correction due to multiple comparison at α=0.001.

30
4. RESULTS
4.1. MICRO-TENSILE BOND STRENGTH (µTBS)
The mean micro-tensile bond strength (µTBS) values and standard deviation (SD) in MPa are
displayed in Table 5 and
Figure 1. Overall, bond strength was influenced by material (p=.000), surface treatment (p=.000),
and age (p=.000).
For leucite, reinforced glass-ceramic groups, the highest bond strength was achieved by group 3
(46.37 ± 16.30) when HF acid is applied for 60 s followed by silane agent. No significant difference
in bond strength between groups 3 (HF 60 s + silane), 4 (MBEP 20+40 s), and 5 (MBEP 20+100
s) were found (p>.001). The negative control (group 1, no surface treatment) yielded the lowest
bond strength, followed by group 2, in which only HF acid etching was employed as a surface
treatment.
After aging, all groups were significantly different than their non-aged counterparts (p<.001),
except for groups 3 (p=.004) and group 4 (p=.004).
For lithium disilicate reinforced glass-ceramic, significantly higher bond strength was achieved by
group 8 (20 s HF + silane) for aged and non-aged groups, followed by group 7, in which HF only
was applied for 20 s. Groups 9 (MBEP 20+40) and 10 (MBEP 20+100) achieved significantly
lower bond strength. Also, significantly more pre-test failures (PTF) were experienced during the
cutting procedure in both non-silanized HF acid, and self-etching ceramic primer when compared
with silanized groups.
After aging, all groups were significantly different than their non-aged counterparts (p<.001),
except for group 8 (p<.0.046).

31
Table 5: Mean micro-tensile bond strength (µTBS) values and standard deviation (SD) in MPa,
number of pre-test failures (PTF) and total sticks
Group
µTBS ± SD
24 h
No. of PTF/Total
Sticks
µTBS ± SD
6 m
No. of PTF/Total
Sticks
Leucite reinforced glass-ceramic (IPS Empress CAD)
1 15.55 ± 10.91
a
0/62 0
a
59/0
2 33.31 ± 11.75
b
0/56 19.41 ± 20.84
b
0/70
3 46.37 ± 16.30
c, A
0/75 36.92 ± 12.76
c, A
0/70
4 41.43 ± 11.39
cd, B
0/66 36.52 ± 12.80
bd, B
0/63
5 44.70 ± 11.75
ce
0/74 38.81 ± 10.67
be
0/77
Values with same lower-case letters in the same column are not significantly different from each other.
Values with same UPPER-case letters in the same row are not significantly different from each other.
Lithium disilicate reinforced glass-ceramic (IPS e.max CAD)
6 0
a, A
50/0 0
a, A
50/0
7 32.35 ± 28.09
b
28/67 5.88 ± 6.58
b
36/65
8 47.31 ± 12.83
c
0/95 39.44 ± 30.77
c, B
2/47
9 12.48 ± 20.81
d
17/27 0.64 ± 4.10
a
39/2
10 12.02 ± 15.58
de
62/59 6.52 ± 11.38
bd
57/44
Values with same lower-case letters in the same column are not significantly different from each other.
Values with same UPPER-case letters in the same row are not significantly different from each other.

Figure 1: Mean micro-tensile bond strength (µTBS) values in MPa for groups 1-10 after 24 hours
and 6 months

0
10
20
30
40
50
Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 Group 9 Group 10
24 Hours 6 Months
Leucite reinforced glass-ceramic Lithium disilicate reinforced glass-ceramic MPa
32
4.2. CONTACT ANGLE OF WATER AFTER DIFFERENT SURFACE TREATMENTS
The mean contact angle values for leucite reinforced glass-ceramic at 0 s, 20 s, 40 s, 60 s, and 120
s are presented in Table 6 and Figure 2 and values for lithium disilicate reinforced glass-ceramic
at 0 s, 20 s, 40 s, 60 s, and 120 s are presented in Table 7 and Figure 4.
Overall, Kruskal-Wallis tests revealed that contact angles differed significantly between the two
ceramic materials (p=.000). Furthermore, surface treatment significantly influenced contact angle
measurement (p=.000), however the time point of measurement did not have any influence
(p=.554).
Group-wise comparison was performed for each material separately. For leucite, reinforced glass-
ceramic contact angle measurements ranged from 0° to 82.85° and based on surface treatment
methods were ranked as followed: MBEP 20+100 = MBEP 20+40 (p=.004) >None> HF = HF +
Silane (p=.131). Time point of measurement did not have any influence on contact angle (p=.851).
Example of contact angle measurement drops on polished leucite reinforce glass-ceramic
specimens with different surface are shown in Figure 3.
Table 6: Mean contact angle (°) for polished leucite reinforced glass-ceramic (IPS Empress
CAD) after different surface treatment at different time points

Surface treatment 0 s 20 s 40 s 60 s 120 s
None 45.57 43.4 42.18 41.3 41.7
HF
a
35.37 24.15 4.72 0 0
HF+Silane
a
15.4 0 0 0 0
MBEP 20+40
b
78.3 74.27 73.07 72.12 74.1
MBEP 20+100
b
82.8 80.1 82.85 78.82 72.73
Treatments with the same lower case letter are not significantly different from each other (p>.001)
33
Figure 2: Mean contact angle values for leucite reinforced glass-ceramic after different
surface treatments at 0, 20, 40, 60 and 120 s.

Figure 3: Contact angle of distilled water at 0 s on polished (600 grit) leucite reinforced glass-
ceramic (IPS Empress CAD) after different surface treatments: a) no surface treatment; b) HF acid
for 60 s; c) HF acid for 60 s and silane for 60 s; d) MBEP agitated for 20 s, left for 40 s; e) MBEP
agitated for 20 s, left for 100 s.

0
20
40
60
80
100
None HF HF+S MBEP 20+40 MBEP 20+100
Contact Angle ( °)
Surface treatment
Contact Angle for leucite reinforced glass-ceramic after
different surface treatments
0 s
20 s
40 s
60 s
120 s
34
For lithium disilicate reinforced glass-ceramic contact angle values ranged from 0° to 75.8° (Table
7, Figure 4). All surface treatment methods used on this ceramic caused contact angles that were
significantly different from each other (p=.000). Time point of measurement did not have any
significant influence on contact angle values (p=.513). Examples of contact angle measurement
drops on polished lithium disilicate reinforced glass-ceramic specimens with different surface are
shown in Figure 5.
Table 7: Mean contact angle (°) for lithium disilicate reinforced glass-ceramic (IPS e.max CAD)
after different surface treatment
Surface treatment 0 s 20 s 40 s 60 s 120 s
Polished only 44..96 42.08 41.56 40.46 39.16
HF 24.45 20.18 19.9 19.74 19.54
HF+S 9.56 8.16 7.66 8.33 7.43
MBEP 20+40 75.8 74.12 73.17 72.65 70.67
MBEP 20+100 53.38 53.65 53.01 49.23 49.61
Treatments with the same lower case letter are not significantly different from each other (p>.001)

Figure 4: Mean contact angle values for lithium disilicate reinforced glass-ceramic after different
surface treatments at 0 s, 20 s, 40 s, 60 s and 120 s.

0
20
40
60
80
None HF HF+S MBEP 20+40 MBEP 20+100
Contact Angle ( °)
Surface treatment
Contact Angle for lithium disilicate reinforced glass-ceramic
after different surface treatments
0 s
20 s
40 s
60 s
120 s
35
Figure 5: Contact angle of distilled water at 0 s on polished (600 grit) lithium disilicate
reinforced glass-ceramic (IPS e.max CAD) after different surface treatments: a) no surface
treatment, b) HF acid for 20 s, c) HF acid for 20 s and silane for 60 s, d) MBEP agitated for 20 s,
left for 40 s, e) MBEP agitated for 20 s, left for 100 s.

36
4.3. CONTACT ANGLE OF DIFFERENT AGENTS ON POLISHED GLASS-
CERAMICS
In addition to the contact angle measurements after surface treatment, contact angles of the agents
themselves were measured on (1) ceramic surfaces polished to 600 grit and (2) ceramic surfaces
polished to 1200 grit as shown in Table 8 and Figure 6.
Kruskal-Wallis test did not show any difference between the two ceramic materials (p=.339) and
time point of measurement (p=.096), but a significant difference between the 600 grit and 1,200
grit surfaces (p=.000).

Table 8: Mean contact angle values (°) of different agents for leucite reinforced glass-ceramic
(IPS Empress CAD) and lithium disilicate reinforced glass-ceramic (IPS e.max CAD)

Group(Agent) Ceramic
Surface
polishing
0 s 20 s 40 s 60 s 120 s
1(W)
Leucite
reinforced
glass-
ceramic
600 grit
45.57 43.4 42.18 41.3 41.71
2(HF) 39.66 32.52 30.98 33.11 31.05
3(S)
a
0 0 0 0 0
4(S2)
a
0 0 0 0 0
5(MBEP) 10.7 0 0 0 0
Agents with the same lower case letter are not significantly different from each other (p>.001)
6(W)
Lithium
disilicate
reinforced
glass-
ceramic
600 grit
44.96 42.08 41.56 40.46 39.16
7(HF) 46.5 39.4 38.8 38.63 37.76
8(S)
a
0 0 0 0 0
9(S2)
a
0 0 0 0 0
10(MBEP) 22.75 0 0 0 0
Agents with the same lower case letter are not significantly different from each other (p>.001)
37
Figure 6: Mean contact angle values of different agents at 0, 20, 40, 60 and 120 s on 600 grit
polished leucite and lithium disilicate reinforced glass-ceramic surfaces: 1/6(W) – Water, 2/7(HF)
– HF acid, 3/8(S) – Silane, 4/9(S2) – Silane after HF acid etching, 5/10(MBEP) – MBEP.

0
10
20
30
40
50
1(W) 2(HF) 3(S) 4(S2) 5(MBEP) 6(W) 7(HF) 8(S) 9(S2) 10(MBEP)
Contact Angle (°)
Contact Angle Agent
Mean contact angle of different agents after 600 grits polishing
of glass-ceramics surfaces
0 s 20 s 40 s 60 s 120 s
38
Glass-ceramics polished to 600 grit
The mean contact angle of different surface treatment agents on leucite reinforced glass-ceramic
specimens, which were polished up to 600 grit are displayed in Table 8 and Figure 6.
For the leucite reinforced glass-ceramic polished with 600 grit alone, time point did not have a
significant influence (p=.851), but the different agents did (p=.000). Group wise comparison for
the different agents are displayed in Table 8.
Examples of contact angle measurements using different agents on polished leucite reinforced
glass-ceramic are displayed in Figure 7.
Figure 7: Contact angle of different agent on leucite reinforced glass-ceramic
a) Water; b) HF acid; c) Silane; d) Silane after HF acid etching; e) MBEP

For lithium disilicate reinforced glass-ceramic polished at 600 grit (Table 8 and Figure 6), time
did not influence contact angle measurements (p=.513), but again the values were dependent on
the agent (p=.000). Group wise comparison is displayed in Table 9. Examples of contact angle
measurements using different agents on polished leucite reinforced glass-ceramic are displayed in
Figure 8.

39

Figure 8: Contact angle of different agent on lithium disilicate reinforced glass-ceramic:
a) Water; b) HF acid; c) Silane; d) Silane after HF acid etching; e) MBEP

40
Glass-ceramic polished to 1,200 grit
The mean contact angles of different agents on glass-ceramics polished up to 1200 grit show the
true wettability of the surface treatment agents on an ideally polished ceramic surface (Table 9,
Figure 9). For both ceramics, time point of measurement did not show any significant influence
(leucite reinforced glass-ceramic: p=.543; lithium disilicate reinforced glass-ceramic: p=.369);
however, for the factor agents significant differences were found (p=.000). Group-wise
comparisons are shown in Table 9.
Table 9: Mean contact angle of different agents for leucite reinforced glass-ceramic and
lithium disilicate reinforced glass-ceramic

Group(Agent) Ceramic
Surface
polishing
0 s 20 s 40 s 60 s 120 s
1(W)
a

Leucite
reinforced
glass-
ceramic
1200 grits
0 0 0 0 0
2(HF) 46.75 36.54 36.78 37.84 24.7
3(S)
a
0 0 0 0 0
4(S2)
a
0 0 0 0 0
5(MBEP)
a
0 0 0 0 0
Agents with the same lower case letter are not significantly different from each other (p>.001)
6(W)
a

Lithium
disilicate
reinforced
glass-
ceramic
1200 grits
30.42 30.75 29.85 26.1 25.2
7(HF)
a
46.4 42.175 41.85 41.525 40.26
8(S)
b
0 0 0 0 0
9(S2)
b
0 0 0 0 0
10(MBEP)
a
22.75 0 0 0 0
Agents with the same lower case letter are not significantly different from each other (p>.001)

41
Figure 9: Mean contact angle values of different agents at 0 s, 20 s, 40 s, 60 s and 120 s on
leucite reinforced glass-ceramic and lithium disilicate reinforced glass-ceramic 1200 grit
polished surfaces: 1/6(W) – Water, 2/7(HF) – HF acid, 3/8(S) – Silane, 4/9(S2) – Silane after HF
acid etching, 5/10(MBEP) – MBEP.

0
5
10
15
20
25
30
35
40
45
50
1(W) 2(HF) 3(S) 4(S2) 5(MBEP) 6(W) 7(HF) 8(S) 9(S2) 10(MBEP)
Contact Angle (°)
Contact Angle Agent
Mean contact angle of different agents after 1200 grits polishing
of glass-ceramics surfaces
0 s 20 s 40 s 60 s 120 s
42
4.4. SCANNING ELECTRON MICROSCOPE MICROGRAPHS
Figure 10: Scanning electron microscopy of intaglio surfaces of a) leucite reinforced glass-
ceramic after surface treatment of HF acid for 60 s; b) leucite reinforced glass-ceramic after surface
treatment of MBEP 20+40, c) leucite reinforced glass-ceramic after surface treatment of MBEP
20+100, d)lithium disilicate reinforced glass-ceramic after surface treatment of HF acid for 20 s;
e) lithium disilicate reinforced glass-ceramic after surface treatment of MBEP 20+40; f) lithium
disilicate reinforced glass-ceramic after surface treatment of MBEP 20+100.

43
5. DISCUSSION
The adhesive bonding of a ceramic restoration to tooth structure involves two distinctive interfaces
that dictate and contribute to the success or failure of the restoration: dentin/enamel- resin interface
and ceramic-resin interface. Both interfaces must be optimized for a successful restorative
treatment.
50
In this study, the focus was mainly directed toward the ceramic-resin interface, the
reliability and durability of resin-cement ceramic bond, after different surface treatments by means
of micro-tensile bond strength test.
For leucite reinforced glass-ceramic, different surface treatments resulted in comparable bond
strength values, except for the negative control groups (1 and 2). However, for lithium disilicate
reinforced specimens, different surface treatment yielded different bond strength to resin-cement.
Therefore, the first null hypothesis that surface treatment would not influence bonding
performance was partially rejected.
The second null hypothesis was also partially rejected since artificial aging, by means of long term
water storage, significantly affected the bond strength values for all groups, except for groups 3A
(HF+silane) and 4A (MBEP 20+40) for leucite reinforced glass-ceramic and group 8A (HF+silane)
for lithium disilicate reinforced specimens.
The wettability of ceramic surfaces after different surface treatments was altered. Therefore, the
third null hypothesis, stating that wettability of ceramic surfaces are not affected by different
surface treatments was rejected. There was no direct correlation of the static contact angles and
the micro-tensile bond strength values. This might indicate that the main mechanism in the bonding
process is the chemical bonding through the silane agent between glass-ceramics and resin-cement.
This is in accordance with other studies proving that silane application plays a major role in bond
stability, especially after aging.
33, 39, 51

44
Wettability of ceramic surfaces
Dynamic or advancing drop contact angle measurements over time was done in this study, these
measurement might be an indication of total surface energy status and wettability.
52
When a drop
has a contact angle of 90° or more, the surface can be described as hydrophobic or “non-wetting”
surface.
53
On the contrary, a surface that has a drop contact angle of less than 90° is more
hydrophilic with higher wettability and higher surface energy.
52
A contact angle close to 0°
indicates complete wetting or spreading of the droplet on the surface.
53

In the present study, all treated surfaces of leucite reinforced glass-ceramic and lithium disilicate
reinforced glass-ceramic presented mean water contact angle values of less than 90°. However,
among them, surfaces treated with self-etching ceramic primer for both glass-ceramics exhibited
higher water contact angle compared to groups treated by HF acid only or HF-silane combination.
This might be explained by the more pronounced etching pattern created by HF acid, which in turn
increased the surface area, liquid penetration, and eventually the wettability as well as total surface
energy.
54
Groups treated with HF acid only or HF-silane combination presented significantly lower
contact angles than all of the other groups, and with advancing time it continues to reduce until it
reaches close to 0°.

For hydrophobic surfaces a high contact angle for the water drop is expected. The compatibility of
hydrophobic surfaces with hydrophobic agents, such as resin cements, would theoretically result
in an increased wettability and improved bonding. However, such finding was not observed in this
study; the contact angle of the water drop on hydrophobic surfaces did not correspond with the
µTBS results. This is a clear indication of the complexity of the adhesion process and the variety
of elements involved.

45
Additionally, there are multiple factors to be considered for optimum bond strength and long-term
durability of the resin-ceramic interfaces. According to Tian et al.
29
these factors include: resin
luting cements, light curing, laboratory test methodology, ceramic type, ceramic crystal structure,
in addition to the surface treatments.

Resin luting cement
The selection of a resin luting material often depends on the type of material, fit of the restoration,
film thickness, and bonding to the tooth requirements.
55

Resin cements can be classified into: etch-and-rinse, self-etch, and self-adhesive resin cements
according to the steps involved in the bonding procedures.
56
Also, chemically-cured, light-cured,
or dual-cured according to their polymerization mode. The resin-cement type plays an important
role in the immediate bond strength and durability of the bond.
57
Chemically-cured resin-cements
have shown to have the highest immediate and long term bond strength.
57
A recent study has shown
that there were no significant differences between chemically-cured and dual-cured resin cement
when bonding to lithium disilicate reinforced glass-ceramic.
58

Generally, chemically-cured materials exhibit slower setting time and lower degree of conversion
(DC) values than light- or dual-cured materials.
59
A high degree of conversion is paramount to the
material physical and mechanical properties.
60
In this study, the rationale behind the selection of
dual-cure resin-cement is the low film thickness of the cement, the high DC, and long term efficacy
of the resulting bond.
61

Laboratory test methodology
The micro-tensile bond strength testing method was first introduced in dentistry by Sano et al.
62
.
Micro-tensile stresses are preferred, due to the uniformity of stresses along the interface, therefore,
46
more adhesive and less cohesive failures are obtained. Also, the smallest surface area of 1 mm
2
or
less, yields higher bond strength values in accordance to the Griffith law.
63
This is mainly
explained by the lower incident of sub-structural flaws within the materials, when a smaller bonded
surface area is utilized. Furthermore, the µTBS allows acquiring multiple specimens from one
sample. The downside to this method is the labor-intensive work nature, associated with
specimens’ preparation and sectioning. For this specific reason, many bond strength studies tend
to utilize other methods, such as shear bond strength (SBS) tests. The SBS test specimen
preparation is less laborious and time consuming. Also, the damage from sectioning and trimming
that is acquired with tensile bond testing is avoided. However, with SBS the incidence of cohesive
failure are higher which is undesirable.
64
This is due to the complex stresses generated on the
specimen’s interface.
65

Long-term water storage is the most commonly used artificial aging technique. It is supposedly
simulating the wet conditions that a bonded interface is exposed to in the oral cavity. However,
clinically, other factors such as stresses due to masticatory forces, thermal changes, and chemical
degradation through enzymes, bacteria, toxins might play an additional role in the degradation of
the adhesive interface. Hydrolysis can occur over a period of time leading to deterioration of the
resin interface by a plasticizing effect of water infiltration into the resin polymer. This might
eventually lead to breakage of resin polymer covalent bonds, resulting in loss of the resin mass,
monomer leaching, and bond degradation.
66
Furthermore, the design of the specimen during
artificial aging does seem to have an influence as well. The aging of smaller stick-shaped
specimens differs from aging of larger specimens. In smaller specimens, the diffusion path for the
water is shorter and therefore faster degradation of the entire adhesive interface is more likely. In
larger specimens on the other hand, diffusion and hydrolysis processes of the whole adhesive
47
interface will take much longer due to increased size and volume of the specimen. Furthermore,
storage media, time, and conditions also have an effect on the durability of the bond.
67

Ceramic type, crystal structure and surface treatment
After surface conditioning, different ceramics exhibit variable microstructures, and surface
topographies, which eventually impact the bond strength between ceramic and resin-cement.
29
In
our study the leucite reinforced glass-ceramic performed better in combination with the self-
etching ceramic primer (MBEP) than the lithium disilicate reinforced glass-ceramic did. This can
be explained by the etching pattern produced on the surface after the application of the self-etching
ceramic primer. Only slight surface modification can be observed when the self-etching ceramic
primer is applied on lithium disilicate reinforced glass-ceramic (Figure 10). On the other hand, a
more pronounced surface modification can be observed on the leucite reinforced glass-ceramic.
This is due to differences in chemical composition and glass content between the two glass-
ceramics.
Due to the novelty of the self-etching ceramic primer, the amount of comparative data is very
limited. No studies have been identified evaluating the bonding performance of the self-etching
ceramic primer on leucite reinforced glass-ceramics. On lithium disilicate reinforced glass-ceramic
two recent studies reported macro- and micro-shear bond data using a self-etching ceramic
primer.
68,69
The reported bond strength values of the groups treated with the self-etching ceramic
primer performed comparably to the conventional surface treatment of etching with HF acid in
combination with silane application. However, these data do not agree with our findings, showing
an inferior performance of the self-etching ceramic primer when compared to the “gold standard”
treatment of HF+silane. The discrepancies could be possibly attributed to the difference in
methodology. While both studies only test bond strength after 24 h our study additionally tested
48
long-term bonding performance after 6 months of water storage. The relevance and clinical
correlation of such short-term data has been questioned.
70
Furthermore, differences in bond
strength testing design can influence the study outcome significantly. For the same materials and
substrates, micro bond strength tests usually yield higher values compared to macro bond strength
studies.
65
Additionally, pre-testing failures are less likely to occur in short term shear-bond strength
studies compared to microtensile bond strength studies, which could skew the data to higher
performance values. In our study, the large number of pretesting failures of the lithium disilicate
glass-ceramic specimens during cutting and long-term storage have resulted in relatively low
microtensile bond strength values.
Our experiment focused solely on the interfacial relation between glass-ceramics, self-etching
ceramic primer, and resin-cement. Tests of the performance of the self-etching ceramic primer in
a cementation model that include the natural tooth substrate might be of interest to evaluate the
efficacy and safety of such agents. Also, studying different restorative materials other than the
tested glass-ceramics will provide wider range for clinician in the selection of restorative materials.
Self-etching ceramic primer might not be the optimal replacement of conventional surface
treatment for glass-ceramics at this time, but it might serve as a safe ceramic repair option intra-
orally for leucite reinforced glass-ceramics.
49
6. CONCLUSIONS
(1) Bond strength to leucite reinforced glass-ceramic using a self-etching ceramic primer is
comparable to using conventional surface treatment of HF acid and silane.
(2) Surface treatment of self-etching primer on lithium disilicate reinforced glass-ceramic
failed to create pronounced surface alteration to aid micromechanical interlocking to resin-
cement and was not as effective as the conventional surface treatment of HF acid and
silane.
(3) Bond durability of self-etching ceramic primer is highly influenced by the type of ceramics
used and their microstructures.
(4) Wettability of glass-ceramic surfaces is impacted by different surface treatments, and
different agents might have diverse surface wetting capabilities depending on the degree
of surface polish and surface energy.

50
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Abstract (if available)

Abstract Objective: The aim of this study is to evaluate the influence of a self-etching ceramic primer on (1) micro-tensile bond strength (μTBS) to leucite reinforced glass-ceramic and to lithium disilicate reinforced glass-ceramic and (2) to examine the wettability of these two glass-ceramics after different surface treatments. ❧ Materials and methods: CAD/CAM blocks made of leucite reinforced (IPS Empress CAD) and lithium disilicate reinforced glass-ceramic (IPS e.max CAD) were cut into 6 mm thick sections and polished with silicone carbide paper up to 600 grit. Resin nanoceramic blocks (Lava Ultimate) of the same size were airborne-particle abraded for 20 s, cleaned and porcelain silane was applied for 60 s. Leucite reinforced glass-ceramic specimens were assigned to the following groups: G1: no surface treatment, G2: 60 s HF acid, no silane, G3: 60 s HF acid, silane, G4: self-etching ceramic primer applied for 20 s and left for 40 s, G5: self-etching ceramic primer applied for 20 s and left for 100 s. For lithium disilicate reinforced glass-ceramic surface treatment protocols were: G6: no surface treatment, G7: 20 s HF, no silane, G8: 20 s HF, silane, G9: self-etching ceramic primer applied for 20 s and left for 40 s, G10: self-etching ceramic primer applied 20 s and left for 100 s. The ceramic specimens were cemented to the resin nanoceramic blocks with a dual-cure resin cement (RelyX Ultimate), then sectioned and subjected to μTBS testing using a universal testing machine (Instron) after 24 h (non-aged) or 6 months (aged) of storage in distilled water. Contact angle for distilled water was measured on both ceramics after different surface treatment. Additionally, contact angles for different agents was measured on polished ceramic surfaces. Ultra-structural analysis of the different surfaces was conducted with scanning-electron microscopy. Statistical analysis of the data was performed using non-parametric (Kruskal-Wallis and Mann-Whitney) tests after Bonferroni correction at α=0.001. ❧ Results: For leucite reinforce glass-ceramic (groups 1-5), μTBS values ranged from 21.45 to 45.15 MPa for non-aged specimens and from 0 to 38.81 MPa for aged specimens. For lithium disilicate reinforced glass-ceramic (groups 6-10), μTBS values ranged from 0 to 45.50 MPa for non-aged specimens and from 0 to 32.10 MPa for aged specimens. Bond strength values were significantly influenced by the factors material, surface treatment, and age (p=.000). For leucite reinforced glass-ceramic, the highest contact angle values were observed for surfaces treated with self-etching ceramic primer, while the lowest contact angle value was achieved by HF 8 acid and silane treated surface. For lithium disilicate reinforced glass-ceramic, the highest water contact angle was recorded on surfaces treated with the self-etching ceramic primer for 20+40 s and the lowest on surfaces treated with HF acid and silane. ❧ Conclusion: Long term efficacy of self-etching ceramic primer is highly dependent on the ceramics' composition and structural arrangement. Wettability of glass-ceramic surfaces is impacted by different surface treatments and agents applied.

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Asset Metadata

Creator Alsobiyl, Haifa A. (author)

Core Title Influence of a novel self-etching primer on bond-strength to glass-ceramics and wettability of glass-ceramics

School School of Dentistry

Degree Master of Science

Degree Program Craniofacial Biology

Publication Date 06/30/2017

Defense Date 05/30/2017

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

Tag bond strength,glass ceramics,OAI-PMH Harvest,self-etching primer,wettability

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Phark, Jin-Ho (committee chair), Duarte, Sillas (committee member), Paine, Michael (committee member), Sartori, Neimar (committee member)

Creator Email alsobiyl@usc.edu,haifa.alsobayel@gmail.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c40-392143

Unique identifier UC11263218

Identifier etd-AlsobiylHa-5472.pdf (filename),usctheses-c40-392143 (legacy record id)

Legacy Identifier etd-AlsobiylHa-5472.pdf

Dmrecord 392143

Document Type Thesis

Rights Alsobiyl, Haifa A.

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the a...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus MC 2810, 3434 South Grand Avenue, 2nd Floor, Los Angeles, California 90089-2810, USA