an in-vitro study

1. Vol 18, No 2, 2016 135
Influence of Surface Conditioning Protocols on
Reparability of CAD/CAM Zirconia-reinforced Lithium
Silicate Ceramic
Rana Al-Thagafia / Walid Al-Zordkb / Samah Sakerc
Purpose: To test the effect of surface conditioning protocols on the reparability of CAD/CAM zirconia-reinforced lith-
ium silicate ceramic compared to lithium-disilicate glass ceramic.
Materials and Methods: Zirconia-reinforced lithium silicate ceramic (Vita Suprinity) and lithium disilicate glass-ce-
ramic blocks (IPS e.max CAD) were categorized into four groups based on the surface conditioning protocol used.
Group C: no treatment (control); group HF: 5% hydrofluoric acid etching for 60 s, silane (Monobond-S) application for
60 s, air drying; group HF-H: 5% HF acid etching for 60 s, application of silane for 60 s, air drying, application of He-
liobond, light curing for 20 s; group CO: sandblasting with CoJet sand followed by silanization. Composite resin (Tet-
ric Evo­
Ceram) was built up into 4 x 6 x 3 mm blocks using teflon molds. All specimens were subjected to
thermocycling (5000x, 5°C to 55ºC). The microtensile bond strength test was employed at a crosshead speed of
1 mm/min. SEM was employed for evaluation of all the debonded microbars, the failure type was categorized as ei-
ther adhesive (failure at adhesive layer), cohesive (failure at ceramic or composite resin), or mixed (failure between
adhesive layer and substrate). Two-way ANOVA and the Tukey’s HSD post-hoc test were applied to test for signifi-
cant differences in bond strength values in relation to different materials and surface pretreatment (p < 0.05).
Results: The highest microtensile repair bond strength for Vita Suprinity was reported in group CO (33.1 ± 2.4
MPa) and the lowest in group HF (27.4 ± 4.4 MPa). Regarding IPS e.max CAD, group CO showed the highest
(30.5 ± 4.9 MPa) and HF the lowest microtensile bond strength (22.4 ± 5.7 MPa). Groups HF, HF-H, and CO
showed statistically significant differences in terms of all ceramic types used (p < 0.05). The control group showed
exclusively adhesive failures, while in HF, HF-H, and CO groups, mixed failures were predominant.
Conclusions: Repair bond strength to zirconia-reinforced lithium silicate ceramics and lithium-disilicate glass ce-
ramic could be improved when ceramic surfaces are sandblasted with CoJet sand followed by silanization.
Keywords: intraoral repair, adhesion, ceramic.
J Adhes Dent 2016; 18: 135–141. Submitted for publication: 26.08.15; accepted for publication: 23.12.15
doi: 10.3290/j.jad.a35909
a Intern, School of Dentistry, Taibah University, Madinah, Saudi Arabia. Prepared
specimens, reviewed literature and contributed substantially to discussion.
b Assistant Professor, Department of Fixed Prosthodontics, Faculty of Dentistry,
Mansoura University, Mansoura, Egypt. Performed the experiments, collected
data.
c Assistant Professor, Department of Fixed Prosthodontics, Faculty of Dentistry,
Mansoura University, Mansoura, Egypt. Experimental design, specimen prep-
aration, data analyis, wrote and edited the manuscript.
Correspondence: Dr. Samah Saker, Fixed Prosthodontics Department, Faculty
of Dentistry, Mansoura University, 35516 El Gomhoria Street, Mansoura, Egypt.
Tel: +20-100-890-6074; e-mail: samah_saker@hotmail.com
Today, all-ceramic restorations are widely used in an at-
tempt to circumvent the esthetic limitations of metal-
ceramic restorations. All-ceramic restorations may be fabri-
cated using a variety of all-ceramic materials and
fabrication techniques. Of the latter, CAD/CAM technology
has been introduced as an alternative to traditional manu-
facturing processes.3,5,15,18,22,27,29 Advances in dental ce-
ramic materials and adhesive technology have expanded
the treatment spectrum for clinicians and technicians and
provided more conservative, simpler all-ceramic restor-
ations with sufficient fatigue resistance to increase the lon-
gevity of CAD/CAM ceramics.16,39,41
Lithium-disilicate glass ceramic is recommended for fab-
rication of highly esthetic restorations in both anterior and
posterior regions in the oral cavity.10 Recently, VITA (Bad
Säckingen, Germany) has introduced a new all-ceramic ma-
terial onto the dental market, Vita Suprinity. Vita Suprinity is
a zirconia-reinforced lithium silicate ceramic with an espe-
cially fine-grained, homogeneous structure for manufactur-
ing crowns in the anterior and posterior area, supracon-
structions on implants, veneers, inlays, and onlays. The
precrystallized blocks are processed in Cerec systems. Sub-
sequently, Vita Suprinity achieves its final esthetic and
physical properties with the final crystallization in a porce-
lain furnace.

2. 136 The Journal of Adhesive Dentistry
Al-Thagafi et al
However, all-ceramic restorations may still fail as a con-
sequence of fractures, cracks, or chipping due to their brit-
tle nature and structural flaws.2,17,34 The removal of frac-
tured ceramic restorations may sacrifice the remaining
sound tooth tissue and weaken the tooth. Repairing such
restorations by bonding composites directly to the exposed
ceramic is cost effective, easy to perform, and offers good
esthetics.8,9,21,26,38 Therefore, while improvements to ce-
ramics continue, it would be beneficial to already have a
predictable means of repairing fractured ceramic restor-
ations as minimally invasively as possible.
Mechanical and chemical bonding protocols have been
recommended to enhance the adhesion of composite res-
ins to all-ceramic restorations.6,13,19,25,28,30-32,36,40 To en-
hance mechanical interlocking, air abrasion with aluminum
oxide particles and surface roughening with a diamond bur
can be performed.1,7,33,37 Chemical bonding using acid
etching with ammonium hydrogen bifluoride or hydrofluoric
acid at different concentrations, followed by application of
an adhesive and coating with silane coupling agents, could
be used to promote bonding to glass ceramics.12,37 As den-
tal ceramics demonstrate varied microstructures, the re-
sponse to different surface treatment protocols to enhance
bond strength to composite resin may also vary.20
To the authors’ knowledge, the literature does not con-
tain an evaluation of the impact of different surface condi-
tioning protocols on the reparability of zirconia-reinforced
lithium silicate ceramic (Vita Suprinity) as compared to lith-
ium-disilicate glass ceramic. Therefore, the purpose of this
laboratory study was to evaluate these parameters. The null
hypothesis was that surface pretreatments have no influ-
ence on the reparability of zirconia-reinforced lithium silicate
ceramic (Vita Suprinity) compared to lithium-disilicate glass
ceramic.
MATERIALS AND METHODS
Specimen Preparation
Rectangular specimens (4 mm x 6 mm x 3 mm) were cut
from lithium-disilicate glass ceramic (IPS e.max, Ivoclar-
Vivadent; Schaan, Liechtenstein) and zirconia-reinforced
lithium silicate ceramic (Vita Suprinity, Vita Zahnfabrik;
Bad Säckingen, Germany) blocks (Shade A1) in the pre-
crystalline stage. The dimensions of each ceramic block
were measured with a digital caliper. Crystallization of ce-
ramic blocks was performed following manufacturers’ rec-
ommendations. The bonded surfaces of ceramic speci-
mens were finished with silicone carbide papers of
different grit sizes (600- to 1200-grit) under copious water
cooling followed by ultrasonic cleaning for 3 min in dis-
tilled water.
Surface Conditioning Protocols
The ceramic specimens in each material group were divided
into four equal subgroups based on the surface condition-
ing protocol used (Table 1), as follows:
y
y Group C, control: bonded ceramic surfaces received no
conditioning.
y
y Group HF: bonded ceramic surfaces were etched with
hydrofluoric acid gel (5% HF) for 60 s, followed by wash-
ing under copious distilled water for 60 s. All speci-
mens were silane coated (Monobond S; Ivoclar
Vivadent) for 60 s and air dried.
y
y Group HF+H: bonded ceramic surfaces were etched
with hydrofluoric acid gel (5% HF) for 60 s, washed, si-
lane coated for 60 s, air dried, and Heliobond was ap-
plied, then light cured for 20 s.
y
y Group CO: bonded ceramic surfaces were subjected to
tribochemical silica coating (CoJet system, 3M ESPE;
Seefeld, Germany) from a short distance (10 mm)
­
perpendicular to the surface at 2.8 bar pressure for
15 s.3,23 In addition, a silane coat (Monobond-S; Ivo-
clar Vivadent) was applied with a clean disposable
brush, let react for 1 min, and air dried for 5 s.
After surface treatments, 3-mm increments of composite
resin (Tetric EvoCeram; Ivoclar Vivadent) were built up and
light cured with a halogen light-curing unit (Hilux Ultra Plus;
Benlioglu Dental), output of 600 mW/cm2, for 40 s. Then
the specimens were stored at 37°C in a distilled water
bath. After 24 h, the specimens were thermocycled for
5000 cycles between 5°C and 55ºC with a 20-s dwell time
and a 5-s transfer time.
Table 1 Experimental groups based on ceramic material, surface conditioning, and aging condition
Groups Substrate Step 1 Step 2 Step 3 Step 4 Step 5
N IPS e.max
Suprinity
No treatment - - Tetric EvoCeram Thermocycling
HF IPS e.max
Suprinity
HF (9.6%) Silane - Tetric EvoCeram Thermocycling
HF-H IPS e.max
Suprinity
HF (9.6%) Silane Bond Tetric EvoCeram Thermocycling
CO IPS e.max
Suprinity
CoJet Silane Tetric EvoCeram Thermocycling

3. Vol 18, No 2, 2016 137
Al-Thagafi et al
Microtensile Bond Strength Test (µTBS)
After thermocycling, the ceramic-composite specimens
were fixed on a metallic base perpendicular to the diamond
disk of a sectioning machine. The initial section (1 mm
thick) was discarded due to the probability of absent or
excessive resin at the resin/ceramic interface that might
falsify the results. Then, three cuts were made at 90-de-
gree angles to each other and the resulting microbars were
re-affixed to the metallic base. The initial section was dis-
carded and 3 to 4 subsequent sections were obtained
(1 ± 0.1 mm2 thick). A light microscope was used for micro-
bar examination and only structurally crack-free, intact bars
were included. A caliper was used to measure the thick-
ness of each microbar. Fifteen microbar specimens of each
group were chosen and their exact dimensions were mea-
sured using a digital caliper before mounting to the jig of
the universal testing machine (Lloyd Instruments; Fareham,
UK) with cyanoacrylate adhesive. The specimens were
loaded in tension at a crosshead speed of 1 mm/min until
debonding.4,14,24 The maximum tensile stress was divided
by the mean of the microbars’ cross sections to obtain
µTBS data (MPa).
Failure Mode Analysis
After debonding, the specimens were examined under a ste-
reomicroscope (Carl Zeiss; Oberkochen, Germany) at 40X
magnification and in a scanning electron microscope (SEM;
JSM-6510LV, JEOL; Tokyo, Japan) at 250X to verify failure
type. The failure type was classified as either adhesive (fail-
ure at the adhesive layer), cohesive (failure in ceramic or
composite resin), or mixed (failure between adhesive layer
and substrate).10
SEM Evaluation
To evaluate the surface topography subsequent to surface
conditioning, three additional samples from each ceramic
group were prepared (no surface treatment, etching with 5%
HF [hydrofluoric acid gel], and tribochemical silica coating)
without the use of silane or the adhesive system. The sam-
ples were rinsed with 96% ethanol and air dried, sputtered
with a gold layer, and then examined using SEM at 1000X
magnification.
Statistical Analysis
The data were tested for normality using the Kolmogorov-
Smirnov and Levene tests before further statistical analysis
(SPSS v19.0 software for Windows, SPSS; Chicago, IL,
USA). Microtensile bond strength results (in MPa) were ana-
lyzed using two-way ANOVA. Tukey’s HSD post-hoc test was
used for multiple comparisons (α = 0.05).
RESULTS
The mean values ± standard deviations (SD) and significant
differences of the microtensile repair bond strengths (μTBS)
for each group are presented in Table 2 and Fig 1. Paramet-
ric ANOVA (Table 3) was performed to evaluate the differ-
ences in the μTBS values among groups, because the data
were normally distributed.
The results of two-way ANOVA showed that both surface
treatment protocol and ceramic type (IPS e.max CAD vs Vita
Suprinity) had a significant effect on the bond strength val-
ues (p < 0.05). Interaction terms were also significant
(p < 0.05).
Regarding IPS e.max CAD, group CO showed the highest
(30.5 ± 4.9 MPa) and HF the lowest microtensile bond
strength (22.4 ± 5.7 MPa). The highest microtensile bond
strength for Vita Suprinity was obtained in group CO
(33.1 ± 2.4 MPa) and the lowest in groups HF
(27.4 ± 4.4 MPa) and HF-H (31.3 ± 3.7 MPa). Tukey’s test
showed a statistically significant difference between differ-
ent surface preparation protocols used (p < 0.05).
Table 2 Means and standard deviations of microten-
sile bond strength values (MPa) for the experimental
groups.
Vita Suprinity IPS.emax CAD Treatment
10.5 ± 2.1a 10.7 ± 2.1a C
27.1 ± 1.4c 22.4 ± 5.7b HF
31.2 ± 3.7d 28.3 ± 4.0c HF-H
33.1 ± 2.4d 30.5 ± 4.9c CO
Identical superscript letters in the same column indicate no significant differ-
ence (Tukey’s test, α = 0.05). C: no treatment; HF: 5% hydrofluoric acid
etching, silane application; HF-H: 5% HF acid etching, application
of silane and Heliobond; CO: sandblasting with CoJet sand followed by
silanization.
Fig 1 Microtensile bond strength values of experimental groups.
Microtensile
bond
strength
(MPa)
40.00
30.00
20.00
10.00
0.00
Surface treatment protocol
No treatment Etching+silane+bond
Type
IPS.emax CAD
Suprinity
Etching+silane tribochemical silica coating

4. 138 The Journal of Adhesive Dentistry
Al-Thagafi et al
DISCUSSION
With the advances in the field of adhesive dentistry, intra-
oral ceramic repair could be considered an integral part of
minimally invasive dentistry. All-ceramic restoration frac-
tures represent a serious problem functionally and estheti-
cally for both patients and dentists. Therefore, instead of
replacing damaged ceramic restorations, it is very important
to search for alternative repair methods that conserve the
remaining sound tooth structure.
In this respect, the achievement of ceramic-composite
bond durability is crucial for long-term clinical success.1,37
Therefore, this study was performed to examine the impact
of surface pretreatment protocols on the reparability of
CAD/CAM zirconia-reinforced lithium silicate ceramic.
The most common drawback of the shear bond strength
test is that it has been associated with the development of
nonuniform stress distributions combined with fracture at a
distance from the interfaces, which may lead to misinterpre-
tation of the results.9,30 In the present investigation, the
microtensile bond strength test was used for repair bond
strength evaluation at the resin/ceramic interface. In this
technique, small-sized specimens are used which allow uni-
form distribution of the loading stress, and failure is mainly
observed at the adhesive interface.24
The current study demonstrated that bonding of compos-
ite resin to CAD/CAM lithium-disilicate glass ceramics was
affected by the surface conditioning protocol used. More-
over, the effect of a particular surface pretreatment de-
pends on the ceramic type, which supports the rejection of
the null hypothesis.
Various ceramic surface treatment protocols including
roughening (CoJet sandblasting) and acid etching followed
by silane application were used in this study. The results
showed that regardless of the type of ceramic material
used, the microtensile bond strength values of group CO
were significantly higher than those of HF-H, HF, and C
groups. This could be explained by the ability of tribochemi-
cal silica coating to incorporate silica particles into the
Regardless of the type of all-ceramic material used, pre-
dominantly adhesive failures were observed in the control
group. Cohesive failures in the composite resin were ob-
served in the HF, HF+B, and CO treated groups, while mixed
failures were observed in all experimental groups. Failure
type frequencies are given by group in Table 4 and repre-
sentative images are shown in Figs 2 and 3.
Scanning electron micrographs of the treated IPS.emax
and Vita Suprinity surfaces are presented in Figs 4 to 6.
The untreated ceramic block showed a smoother surface
pattern than did the 5% HF-acid-etched ceramic block
(Fig 3). Uniform honeycomb-like microrough, porous sur-
faces were observed on the 5% HF-acid-etched ceramic
block (Fig 4). Overall coarse surface irregularities were
found on the tribochemically silica-coated ceramic com-
pared to the other treated groups (Fig 5).
Table 3 Two-way ANOVA, comparison of means of microtensile bond strength (μTBS) of composite resin to ceramic
substrate (MPa)
Source Type III Sum of Squares df Mean Square F Significance
Corrected Model 8514.232a 7 1216.319 79.340 0.001
Intercept 71022.677 1 71022.677 4632.765 0.001
Type 201.528 1 201.528 13.146 0.001
Treatment 8211.643 3 2737.214 178.547 0.001
Type * treatment 101.061 3 33.687 2.197 0.092
Error 1717.018 112 15.331
Total 81253.926 120
Corrected Total 10231.249 119
Table 4 Failure patterns by group
Treat-
ment
Material Failure (%)
Adhesive Mixed Cohesive
Control
Vita Suprinity 80 20 0
IPS.emax CAD 93.3 6.7 0
HF
Vita Suprinity 0 93.3 6.7
IPS.emax CAD 13.3 80 6.7
HF-H
Vita Suprinity 6.7 73.3 20
IPS.emax CAD 0 86.7 13.3
CO
Vita Suprinity 0 80 20
IPS.emax CAD 6.7 80 13.3
HF: 5% hydrofluoric acid etching, silane application; HF-H: 5% HF acid
etching, application of silane and Heliobond; CO: sandblasting with CoJet
sand followed by silanization.

5. Vol 18, No 2, 2016 139
Al-Thagafi et al
Fig 4 SEM micrographs (1000X) of un-
treated surfaces of Vita Suprinity (a) and
IPS.emax CAD (b) showing homogeneous,
smooth surface topography.
Fig 5 SEM micrographs (1000X) of 5% HF
treated surfaces of Vita Suprinity (a) and
IPS.emax CAD (b) showing uniformly micror-
ough, porous surface topography.
Fig 2 SEM micrographs (250X) of debonded surfaces of Vita Suprinity showing a) mixed failure mode, b) adhesive failure mode, c) cohesive
failure mode.
Fig 3 SEM micrographs (250X) of debonded surfaces of IPS.emax CAD showing a) mixed failure mode, b) adhesive failure mode, c) cohesive
failure mode.
Fig 6 SEM micrographs (1000X) of tribo-
chemical silica-coated surfaces of Vita Su-
prinity (a) and IPS.emax CAD (b) showing
overall coarse surface irregularities.
a b c
a b c
a b
a b
a b

6. 140 The Journal of Adhesive Dentistry
Al-Thagafi et al
­
surfaces and enhance the chemical bond between coated
silica, silane, and composite resin.9
This result was similar to that found by Rüttermann et
al,36 who reported that the use of tribochemical silica coat-
ing followed by silane application improved the bond
strength to glass-ceramic restorations compared to HF acid
etching. However, this was not supported by Erdemir et
al,13 who reported that conditioning of glass ceramic with
tribochemical silica coating and silane application demon-
strated a decrease in bond strength values compared to
conventional etching with HF.
In this study, the use of chairside tribochemical silica
coating improved the repair bond strength of the zirconia-
reinforced lithium silicate ceramic vs the lithium-disilicate
ceramic. This could be attributed to its ZrO2 content of ap-
proximately 10% by weight, which could affect bonding.
Regarding improvement of bonding efficacy in group
HF-H – in which the bonded ceramic surfaces were sub-
jected to etching and silanization followed by application
of an adhesive resin (Heliobond) – El Zohairy et al12 dem-
onstrated that the use of a hydrophobic adhesive resin
plays a critical role in enhancing the durability at the adhe-
sive interface. They reported that, even after storing spec-
imens in water for 28 days, the adhesive interfacial bond
remained stable after the use of a hydrophobic bonding
agent. In contrast, Reich et al37 and Peumans et al33 con-
cluded that for the improvement of the repair bond
strength to glass ceramics, there is no need to use a
bonding agent; however, silanization after etching could be
enough for clinical use.
For silica-based ceramic repair, several studies recom-
mend the use of hydrofluoric acid plus silane coupling.
Etching with HF acid creates surface roughness and in-
creases the surface area for micromechanical retention by
selective dissolution of the glass matrix from the ceramic
surface.12,13,26,28 Silane coupling agents act as adhesion
promoters used on glass ceramics to promote adhesion.
During resin curing, bonding of silane coupling agents to
composite resin occurs between silane molecules and
methacrylate groups of the matrix resin through an addition
polymerization reaction. However, the silanol groups of the
hydrolyzed molecule of silane form a siloxane network with
the silanol groups in the treated ceramic surface through a
condensation reaction.9,37
Poor results were shown by the control group in this
study, where the failure mode was predominantly adhesive,
suggesting that in the resin-ceramic bond, the weak link
could be present at the interface.
Although laboratory tests are important to determine ma-
terial properties and rank their performances, the results
cannot be applied to the clinical situation without clinical
evaluation. Therefore, long-term clinical evaluations of
these materials are recommended.
CONCLUSIONS
Based on the present findings, it can be concluded that 1.
repair bond strength of CAD/CAM lithium-disilicate glass
ceramics was influenced by the surface treatment protocol
used, and 2. the use of tribochemical silica coating (Cojet
Sand) followed by silanization, as well as etching followed
by silanization and bonding increased the bond strength to
CAD/CAM lithium-disilicate ceramics.
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Clinical relevance: Considering both the bond strength
results and the failure types after aging, etching fol-
lowed by silanization and bonding or sandblasting with
Cojet sand followed by silanization can be recom-
mended as surface treatment regimens for intraoral re-
pair of CAD/CAM lithium disilicate ceramics with
composite resin repair material.