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Author’s Accepted Manuscript
Effects of multiple firings on mechanical properties
and resin bonding of lithium disilicate glassceramic
Hongliang Meng, Haifeng Xie, Lu Yang, Bingzhuo
Chen, Ying Chen, Huaiqin Zhang, Chen Chen
www.elsevier.com/locate/jmbbm
PII:
DOI:
Reference:
S1751-6161(18)31067-1
https://doi.org/10.1016/j.jmbbm.2018.08.015
JMBBM2926
To appear in: Journal of the Mechanical Behavior of Biomedical Materials
Received date: 23 July 2018
Revised date: 15 August 2018
Accepted date: 19 August 2018
Cite this article as: Hongliang Meng, Haifeng Xie, Lu Yang, Bingzhuo Chen,
Ying Chen, Huaiqin Zhang and Chen Chen, Effects of multiple firings on
mechanical properties and resin bonding of lithium disilicate glass-ceramic,
Journal of the Mechanical Behavior of Biomedical Materials,
https://doi.org/10.1016/j.jmbbm.2018.08.015
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Effects of multiple firings on mechanical properties and resin bonding of lithium
disilicate glass-ceramic
Hongliang Meng1, Haifeng Xie1, Lu Yang1, Bingzhuo Chen1, Ying Chen1, Huaiqin
Zhang1, Chen Chen2*
1
Jiangsu Key Laboratory of Oral Diseases; Department ///of Prosthodontics, Affiliated
Hospital of Stomatology, Nanjing Medical University, Nanjing, China.
2
Jiangsu Key Laboratory of Oral Diseases; Department of Endodontics, Affiliated
Hospital of Stomatology, Nanjing Medical University, Nanjing, China.
*
Corresponding Author: Dr. Chen Chen, Han-Zhong Road 136th, Stomatological
Hospital of Jiangsu Province, Nanjing 210029, China, Tel: +8625 8503 1822, Fax:
+8625 8651 6414, E-mail: ccchicy@njmu.edu.cn
Abstract
Objectives:
This study aimed to evaluate the effects of different firing cycles on surface hardness,
fracture toughness, and roughness of lithium disilicate glass-ceramic, as well as their
bond strength to resin.
Materials and Methods:
A total of 320 polished lithium disilicate glass-ceramic plates were assigned to four
main groups (n=60) to receive one, two, three, or four firing cycles, respectively.
Ceramic plates of the four groups were conditioned with HF acid followed by
silanization. The pre-treated ceramic plates were cemented with composite resin
cylinders using conventional or self-adhesive resin cements to build bonded
specimens, and submitted to shear-bond-strength (SBS) testing after water storage for
24 h or 3 mo at 37°C. The ceramic received different firing cycles after polishing or
HF etching was observed using a scanning electron microscope, and their surface
roughnesses were determined by a profilometer. The surface Vickers hardness,
fracture toughness, and related Weibull analysis results of the polished ceramics after
undergoing different firing-cycle times were compared.
Results:
One sintering significantly increased fracture toughness of lithium disilicate
glass-ceramic; however, multiple firing cycles failed to increase it further. Weibull
analysis revealed a significant difference in terms of structural reliability among the
specimens receiving 0–4 firing cycles. Specimens that received no firing cycle
showed the highest surface hardness. Multiple firing cycles had no significant
influence on the surface Vickers hardness and surface roughness. HF etching
increased surface roughness, and the roughened surface improved the resin SBS of
lithium disilicate glass-ceramic. Multiple firing cycles had no significant effect on
surface roughness. Furthermore, multiple firing cycles and 3-mo water storage had no
significant effect on the SBS.
Conclusions:
The mechanical properties of lithium disilicate glass-ceramics would be partially
affected by multiple firing cycles, while their resin bonding would not be.
Graphical abstract
Keywords: multiple firings; lithium disilicate glass-ceramic; shear bond strength;
Weibull analysis; surface hardness; surface roughness
1. Introduction
Chair-side computer aided design/computer aided manufacturing (CAD/CAM)
has enjoyed growing popularity in dental clinics due to the benefits of a reduced visit
times, high precision of restoration, and automation of procedures (Addison et al.,
2012; Li et al., 2014). Several kinds of all-ceramic systems are market-available.
Lithium disilicate glass-ceramics have now been widely used because they combine
outstanding aesthetic appearance with high strength (Song et al., 2016; Marcos et al.,
2018). Lithium metasilicate maintains a partially crystallized status that makes it
easier to cut and grind (Li et al., 2014; Alao et al., 2017; Hallmann et al., 2018);
however, it requires at least one firing cycle to fulfill the crystallization process to
improve its strength and aesthetics to simulate natural tooth (Li et al., 2014). Its
crystallized flexural strength, ranging from 130 to 360 MPa, can satisfy the need of
occlusion (Li et al., 2014). Due to the limit of the finished colors of lithium disilicate
blocks, glazing or veneering on the surface of lithium disilicate restorations is
required to produce esthetic appearance (Li et al., 2014; Jalali H et al., 2016).
Moreover, if a deficient proximal contact is found after locating a lithium disilicate
glass-ceramic restoration, or characteristic dying is needed for esthetic purposes,
additional firing cycles are required (Rifat et al., 2014; Jalali H et al., 2016; Funda
Bayindir and Ozlem Ozbayram., 2018). Hence, prior to cementing on tooth substrate,
a lithium disilicate glass-ceramic restoration might undergo at least two or more firing
cycles (Rifat et al., 2014).
Mechanical properties contribute much to a long-term clinical service of lithium
disilicate glass-ceramic restorations (Song et al., 2016). Lithium disilicate
glass-ceramics are composed of an interlocking microstructure of a glass matrix and a
crystalline phase. This microstructure, which provides an effective strengthening and
aesthetic performance (Tang et al., 2014), is created by controlled crystallization of
different components achieved through controlling heat treatments (Serbena et al.,
2015; Hallmann et al., 2018).
Studies have shown that heat treatments were associated with the structural and
mechanical changes of the ceramic, and the mechanical properties of lithium disilicate
glass-ceramics depended on microstructure (Hallmann et al., 2018; Yuan et al., 2013).
Changes in the morphology of the crystalline structure of lithium disilicate
glass-ceramics after heat treatments at different temperatures and times have
previously been reported, wherein sintering time had no significant effect on the
composition of the crystalline phases but affected crystal size (Yuan et al., 2013; Auré
lio et al., 2017) and flexural strength (Yuan et al., 2013) significantly. The influence
of sintering time on flexural strength showed a time dependence: 1–5 h sintering led
to its increase while a further extension of up to 5–8 h led to a decrease (Yuan et al.,
2013). Firing-cycle times were found that might affect the mechanical properties of
silica-based ceramic; according to Tang et al., the fracture toughness and surface
Vickers hardness of a pressable lithium disilicate glass-ceramic decreased
significantly after two heat-pressing procedures, a change that was considered to be
caused by the changes of density and porosity of the ceramics (Tang et al., 2014).
Although the most firing cycles of kinds of lithium disilicate glass ceramic can be
related to a study that investigated the effects of one, three, five, and seven firing
cycles on flexural strength, reporting that multiple firing cycles of up to seven had no
significant effect on flexural strength (Rifat et al., 2014), firing protocols usually
apply within one to four times in clinical procedures, such as glazing, staining, and
shape corrections, as mentioned above; hence, the effects of three to five firing cycles
should be investigated.
Apart from mechanical properties, due to its essential brittleness and lower
mechanical properties compared to high-strength ceramics, e.g., zirconia, long-term
clinical service of lithium disilicate glass-ceramic restorations also rely on a durable
resin bonding to tooth abutment (Tian et al., 2014). Similar to the other kind of
silica-based ceramics, it is widely accepted that the resin bonding of lithium disilicate
glass-ceramic depends on both the micro-mechanical retention achieved by
roughening the ceramic surface and the chemical bonding between the chemically
active ceramic surface and resin matrix in resin cement (Lee et al., 2017; Guarda et al.,
2013). Etching with HF followed by the application of silane coupling agent is the
most commonly used bonding strategy (Lung et al., 2012; Tian et al., 2014; Lee et al.,
2017). Roughening lithium disilicate glass-ceramic with HF etching is based on the
mechanism of HF acid reacting with silica in a ceramic substance to form soluble
fluorosilicate (Marcos et al., 2018), since the glass phases and crystalline phases in
lithium disilicate glass-ceramic would be restructured and rearranged during the
crystallization process with heating treatment as mentioned above. Whether different
firing cycle times might lead to microstructure changes and whether microstructure
changes would further affect the acid resistance must be investigated. In addition,
silane is a bi-functional molecule, which is capable of binding to silica as well as of
co-polymerizing with the unsaturated carbon bond of the unpolymerized resin matrix.
Furthermore, knowing whether silanization would be affected by the alternations of
microstructure of lithium disilicate glass-ceramic due to different firing cycles is
valuable.
Accordingly, the aim of this study was to evaluate the effects of different
firing-cycle times on surface hardness, fracture toughness, and roughness of lithium
disilicate glass-ceramic, as well as their bond strength to resin. The null hypotheses
tested were: (i) multi-firing cycles had no effects on mechanical properties, and (ii)
resin bonding of lithium disilicate glass-ceramic.
2. Materials and Methods
2.1. Ceramic fabrication and sintering
Three hundred and twenty bar-shaped lithium disilicate glass-ceramic plates (12
× 12 × 2 mm3) were cut from machinable lithium disilicate blocks (57%–80% SiO2,
11%–19% Li2O, IPS e.max CAD, Ivoclar Vivadent, USA) with a low-speed saw
(Isomet 1000, Buehler Ltd., Lake Bluff, IL, USA). All of the specimens were
wet-polished using 600-, 800-, 1000-, 1200-, and 1600-grit silicon carbide abrasive
papers in order with a rotational polishing device (PG-1, BiaoYu instrument, Shanghai,
China), and then were divided into four groups to subject to one, four, three, or four
firing cycles. These heating schedules were performed in a crystallization furnace
(Ivoclar Vivadent Programat P3000, USA) with a single heating procedure following
the manufacturer´s instructions: sintered in the programmed dental furnace at a
stand-by temperature of 403°C, then heated to 830°C at a heating rate of 90°C/min
and held for 10 min. Next, heating was performed to 850°C at a speed of 30°C/min
and held for 7 min. Finally, the specimens were cooled to 700°C at a speed of
20°C/min and then naturally cooled to room temperature.
2.2. Surface Vickers hardness, fracture toughness, and Weibull analysis
Forty polished lithium disilicate glass-ceramic plates that had received zero to
four firing cycles were submitted to an indention test to measure the surface hardness
and fracture toughness (n=8). Indentations were created using a Vickers
microhardness tester (FM-700, Future-Tech Corp, Kanagawa, Japan) with a constant
load of 9.807 N for 10 s. The diamond indentations were assessed using scanning
electron microscopy (SEM, LEO 1530VP, Oberkochen, Germany) at 15 kV at 5000×
magnification.
The Vickers hardness was calculated according to:
 = 0.1891/2 , (1)
where  is the load at fracture (N) and  the mean half-diagonal length left by the
indenter (mm). Then, the fracture toughness was evaluated according to(Tang et al.,
2012):
 = 0.016 × ( ⁄ )1/2 × (⁄ 3/2 ), (2)
1
where  is the fracture toughness (MPa·2 ),  the modulus of elasticity (GPa),
 the Vickers hardness obtained by the Vickers hardness test ( ) ,  the
indentation load (N), and  the mean half-length of the radial cracks from the
impression center (mm).
After examining the normal distribution and homogeneity via Levene tests,
one-way analysis of variance (ANOVA), and post-hoc tests [Tukey’s honestly
significant difference; (HSD)] (for multiple comparisons) were performed to examine
the effects of the firing-cycle times on surface Vickers hardness and fracture
toughness. Statistical analyses were performed using SPSS 22.0 statistical software
(SPSS Inc., Chicago, IL, USA). Statistical significance was pre-set at α=0.05.
Weibull analysis was used to analyze the reliability of fracture toughness test.
For each of the five groups (n=8), the fracture toughness values of each group were
arranged in ascending order as follows: =1,2,3,…,, where  is the rank number of
each data and  the total number of specimens in each group that represents the
order of the maximum value. The probability of failure for each fracture toughness
value ( ) was calculated with the following formula:
 = ( − 0.5)⁄ . (3)
Then, least-squares estimation (LSE), maximum-likelihood estimation (MLE), and
mean and variance evaluation were used to evaluate each material and treatment
group using a scale parameter  and the Weibull modulus m (two-parameter

Weibull distribution) with the following formula:  = 1 − exp{−( ⁄ ) }, (4)
where  is the probability of failure at or below the stress  . The subsequent
calculations were derived fromlnln[1⁄(1 −  )] = ln − ln . (5)
The plotting of lnln[1⁄(1 −  )] against  provided a slope with the value 
(Weibull modulus) and an intercept ln .
2.3. Shear bond strength tests
Two hundred and forty polished lithium disilicate glass-ceramic plates received
one to four firing cycles from each group were etched with 9.5% buffered
hydrofluoric (HF) acid gel (Bisco, USA) for 20 s, rinsed for 1 min, cleaned
ultrasonically for 5 min, air dried, and then conditioned by a silane coupling agent
(Monobond N, Ivoclar Vivadent, USA) and dried with an oil-free air syringe after
natural volatilization for 30 s.
Two hundred and forty pre-polymerized resin composite (Valux Plus, 3M ESPE,
MN, USA) cylinders 6 mm in diameter and 3 mm thick were prepared.
The pre-treated ceramic plates were assigned into eight groups (n=30) according
to the number of firing cycles and the resin cements used. These groups were
designated the firing-cycle times (from 1 to 4) followed by the abbreviations of the
resin cements (RV for Rely X Veneer Cement, 3M ESPE, MN, USA; and RU for Rely
X Unicem Cement, 3M ESPE). Pre-polymerized resin composite cylinders were
cemented on a pre-treated ceramic plate surface with a layer of resin cements under a
constant load. Each bonded specimen was light-cured with a LED lamp (1000
mW/cm2, Elipar FreeLight 2, 3M ESPE, Seefeld, Germany) at six different locations
for 40 s each after removal of the excess cement.
Half of the specimens for each group were stored in distilled water at 37°C for
24 h and underwent shear-bond-strength (SBS) testing with a universal testing
machine (Instron Model 3365, ElectroPuls, MA, USA) at a speed of 1 mm/min.
Another half of each group was tested after 37°C water storage for 3 mo. The loading
fracture load (N) was recorded and the SBS value calculated according to the formula
 = /, (6)
where F is the loading fracture load (N) and S the adhesive area (mm2).
ANOVA and Tukey tests were performed to evaluate the effects of firing-cycle
times, kinds of resin cements, aging, and their interaction on the SBS after passing
normally distributed and equal-variance tests. Statistical significance was also pre-set
at α=0.05.
The types of bond-failure modes of each bonded specimen after SBS testing
were also determined (Schwenter et al., 2016): adhesive (failure occurred in the
interface), cohesive (failure occurred in the resin cement or composite resin cylinders),
and mixed (failure occurred partially in the specimen material, partially at the
interface).
2.4. Surface roughness and morphological observation
Thirty lithium disilicate glass-ceramic plates receiving zero to four firing cycles
with and without HF etching were prepared (n=3) for the evaluation of surface
roughness (Ra) using a surface profilometer (contour GT-X 3D optical microscope,
Bruker, Billerica, MA, USA). Each Ra value (μm) was derived from the mean reading
value of three observation areas.
Another 10 lithium disilicate glass-ceramic plates received zero to four firing
cycles with and without HF etching and were submitted to morphologic observation.
All of the specimens were sputter-coated with Au for examination with a scanning
electron microscope (LEO 1530VP, Oberkochen, Germany) in the secondary electron
imaging mode, at magnifications of 5000×. Observation parameters were accelerating
voltage 10 kV and working distance 9 mm.
3. Results
3.1. Surface Vickers hardness, fracture toughness, and Weibull analysis
Surface hardness results for the five groups are presented in Fig. 1. The Levene
test showed that surface Vickers hardness data were normally distributed and
exhibited equal variance. The results of one-way ANOVA and Tukey tests showed that
different firing-cycle times significantly affected surface hardness. The highest
surface hardness value was observed before sintering. The surface hardness of one to
four firing cycles showed no statistical significance, although both were lower than
the one before sintering.
Fracture toughness results for the five groups are presented in Fig. 2. The Levene
test showed that fracture toughness data were normally distributed and exhibited
equal variance. One-way ANOVA and Tukey tests showed that different firing-cycle
times had significant effects on the fracture toughness. Lithium disilicate
glass-ceramic presented the lowest fracture toughness before sintering. Significantly
higher fracture toughness data were obtained after one to four firing cycles. However,
the fracture toughness decreased reversedly after the second sintering; nevertheless,
this decreasing trend did not continue since non-significant fracture toughness values
were observed among the groups receiving two or more firing cycles.
The Weibull statistical parameters are presented in Table 1. Higher Weibull
modulus means smaller error range and a higher level of structural integrity, as well as
a potentially greater structural reliability of the material. Statistical analysis revealed
significant differences among the fracture toughness values obtained for all of the
tested groups. The specimens that did not experience a firing cycle showed the lowest
mean fracture toughness values and Weibull moduli. Weibull plots for all of the
experimental groups with 95% confidence interval are shown in Fig. 3.
3.2. Shear bond strength
The mean SBS values and standard deviations of all groups are shown in Table 2.
The Levene test showed that SBS data were normally distributed and exhibited equal
variance. Three-way ANOVA revealed that there was no significant difference among
all groups, indicating that no significant difference was found among the different
numbers of firing cycles, between the resin cements used, and with 24 h or 3 mo of
water storage. After 3 mo of water storage, the SBS values of all of the groups
decreased slightly, but not significantly.
The failure mode analysis (Fig. 4) revealed the most mixed failures for all of the
groups, regardless of number of firing cycles, types of resin cements, and duration of
water storage.
3.3. Surface roughness and morphological observation
Figure 5 shows the representative three-dimensional images of the specimens
after HF acid etching and polishing. The images revealed that specimens after
polishing showed a relative smooth surface, apart from some scratches produced in
the preparation of the specimens. Much rougher surfaces were observed after HF
etching. The mean surface roughness values and their standard deviations of all of the
groups after different firing cycles with and without HF etching are presented in Table
3. One-way ANOVA revealed that there was no significant difference among groups
receiving zero to four firing cycles, regardless of etching with HF or polishing.
However, the surface roughness values (Ra) were significantly increased after HF
etching. No significant interaction was found between firing cycle times and
HF-etching on surface roughness.
SEM images (Fig. 6) further highlighted that the surfaces in the HF-etched
specimens showed statistically significant higher roughness values than the polished
ones. The polished surface seemed relatively smooth without obvious pores, except
for the polishing traces and scratches. SEM images showed no obvious alternations
among morphology of all polished specimens received different numbers of firing
cycles. However, the specimens receiving zero to four firing cycles produced different
surface morphologies after etching with HF. As is evident from Fig.6, the partially
crystallized specimen that received no sintering showed a porous honeycomb
microstructure after HF etching. The fully crystallized specimens that received one to
four firing cycles showed a highly interlocking microstructure consisting of
long-needle-shaped lithium disilicate crystals that were exposed by the dissolving of
the glass matrix after etching with HF acid.
4. Discussion
The aim of this in vitro study was to evaluate the effects of different numbers of
firing cycles on the mechanical properties and resin bonding of lithium disilicate
glass-ceramics. The mechanical properties, including fracture toughness and surface
hardness, in addition to the surface roughness of lithium disilicate glass-ceramics that
received different numbers of firing cycles were studied. The study also evaluated the
SBS of resin bonding of lithium disilicate glass-ceramics that received different
numbers of firing cycles when HF etching and silanization were adopted. Based on
the results obtained, the null hypothesis can therefore be partially rejected, since the
firing-cycle times had no significant effect on the surface roughness, surface Vickers
hardness, and the SBS, but significantly affected fracture toughness.
The present study adopted both fracture toughness and surface hardness tests to
evaluate the mechanical properties of lithium disilicate glass-ceramics. Fracture
toughness is an intrinsic property that describes the material’s ability to resist crack
propagation under external force. Surface hardness, which has been considered a
criterion by which to evaluate occlusal wear resistance of materials (Homaej et al.,
2016), reflects the ability of a ceramic surface to resist deformation or damage
(Lauvahutanon et al., 2014). According to the obtained results, the fracture toughness
of lithium disilicate glass-ceramic increased significantly after one firing cycle, which
should be due to the strengthened microstructure obtained by crystallization after
firing cycle (Badawy et al., 2016). This increase in fracture toughness is beneficial to
hindering crack propagation, resulting in effective strengthening (Zhao et al., 2015).
Interestingly, it was noticed that the ceramic plates that received one firing cycle
showed the highest fracture toughness, even when compared to those that received
multiple firing cycles. A similar result was also shown in a previous study, in which
the fracture toughness of pressable lithium disilicate glass-ceramic was found to be
significantly lower after two heat-pressings (Tang et al., 2014). Some authors gave the
reason for this as, after two heat-pressings, the changes of orientation of the lithium
disilicate crystals, and porous microstructure in pressable lithium disilicate
glass-ceramic may cause cracks to propagate more easily, causing a lower fracture
toughness of the ceramic (Wang et al., 2013). We assumed that multiple firing cycles
are responsible for the change of fracture toughness of lithium disilicate glass-ceramic,
instead of agreeing that the action of heat-pressing led to the decrease of fracture
toughness, because heat-pressing was not applied in the present study. Weibull
statistical analysis was also employed to analyze the fracture toughness values to
confirm the reliability of the fracture toughness test. The group that received no firing
cycles showed the lowest Weibull moduli, while the Weibull distribution presented
higher shape values for specimens that received one to four firing cycles; however,
the  value did not increase along with the increasing number of firing cycles,
suggesting that the structural integrity and consistency of lithium disilicate
glass-ceramic were improved after one sintering, but the multiple firing cycles would
not improve them further.
The lithium disilicate glass-ceramic plates presented similar performance
between the present surface hardness and fracture toughness tests. The ranges of the
obtained surface hardness values are well matched with previously reported data
(Homaei et al., 2016), suggesting the effectiveness of the present surface hardness test.
According to the results of the present surface hardness test, a significant decrease in
surface hardness was found after even one firing cycle; fortunately, no further change
was found with increasing number of firing cycles, suggesting that multiple firing
cycles, within four, do not harm the surface hardness of lithium disilicate
glass-ceramic. This result is consistent with that of previous studies (Özdemir et al.,
2018). However, previous conclusions regarding the effects of firing cycles on the
surface hardness of lithium disilicate glass-ceramic do not seem to always be
consistent. Apart from the fracture toughness results mentioned above, Tang et al.
reported that the surface Vickers hardness of lithium disilicate glass-ceramic after two
heat-pressings was also significantly lower than that after one heat-pressing, and
considered that this change are likely caused by the changes of density and porosity of
the ceramics (Tang et al., 2014). To address whether multiple firing cycles would
influence the microstructure of lithium disilicate glass-ceramic, which in turn would
potentially impact the mechanical properties, SEM was used to observe the
microstructure and morphology of ceramic surface. According to SEM observations,
there is no visual difference in the surface porosity and morphology for ceramic plates
that received different numbers of firing cycles, which might be the reason why the
surface hardness and fracture toughness in the present study were not affected by
multiple firing cycles. Some studies have reported the effects of sintering on the
microstructure of lithium disilicate-glass ceramic in which the ceramic became denser,
the voids in the microstructure disappeared after sintering (Yuan et al., 2013; Homaei
et al.,2016), and the porosity increased after heat-pressing (Tang et al., 2014).
However, it was also reported in another study that a homogeneous surface consisted
of a dense union between glassy and crystalline phases without voids or gaps
(Murillo-Gómez et al., 2018). We must acknowledge that the present study cannot
explain such totally different results among these previous studies, only to say further
studies are needed.
Compared to other kinds of silica-based ceramics, lithium disilicate
glass-ceramic has higher mechanical strength and toughness; however, innate
brittleness is still a disadvantage when compared to oxide ceramics, such as zirconia
and alumina. Hence, the long-term clinical serving of restorations is highly dependent
on the adhesion between luting cement and ceramic (Tian et al., 2014; Schwenter et
al., 2016; Lee et al., 2017). Compared with conventional cements, including glass
ionomer or zinc phosphate cements, resin cements are beneficial for long-term
success of silica-based ceramic restorations and are preferred to be used for luting this
kind of restoration in clinical settings (Hitz et al., 2012). Bonding between organic
resin and inorganic ceramic depends on both mechanical interlocking and chemical
affinity. Surface roughness is an important parameter known to affect ultimate bond
strength, not only increasing the surface area for bonding, but also providing
micro-interlocking to luting cement (Asiry et al., 2018). The present SEM
observations after HF etching found similar rougher surfaces for lithium disilicate
glass-ceramic that received one to four firing cycles. Studies found that HF can react
with silicon dioxide in lithium disilicate glass-ceramic to form a soluble
hydrofluorosilicate, resulting in the exposure of lithium disilicate crystals that form a
special interlocking microstructure (Guarda et al., 2013; Tang et al., 2014; Sundfel et
al., 2016). It has also been suggested that HF etching leads to the dissolution of the
lithium orthophosphate crystals located in the glass matrix and at the lithium disilicate
crystal grain boundaries, because the lithium orthophosphate phase had a higher
etching rate than that of the lithium disilicate phase (Tang et al., 2014). The present
SEM images matched these interpretations well, because these rougher surfaces of
ceramic that received one to four firing cycles shown in the present SEM images can
be described as such a kind of crystal-interlocked morphologies. Nevertheless, the
totally different roughened surface between the ceramic with sintering and that
without suggested to us that partially crystallized lithium disilicate glass-ceramic
presented weaker HF-acid resistance than the crystallized ones. Moreover, once the
lithium disilicate glass-ceramic fulfilled crystallization, multiple firing cycles exerted
no detectable influence on its microstructure and HF-acid resistance. This conclusion
is also supported by the present surface roughness test results, since no difference in
surface roughness was found among ceramic plates that received different numbers of
firing cycles. Previous studies found that with increasing number of firing cycles, the
surface finish of lithium disilicate glass-ceramic increased and the surface roughness
decreased (Gonuldas et al., 2014); however, both the present SEM observation and
surface roughness test failed to detect this kind of change. Nevertheless, based on the
results of the present surface roughness test, it is safe to say that multiple firing cycles
had no significant effect on roughness, resulting in similar micro-mechanical retention
between the ceramic and resin.
Application of a silane coupling agent after HF etching is a well-accepted
surface-treatment protocol for bonding silica-based ceramics, including lithium
disilicate glass-ceramic (Lung and Matinlinna, 2012; Tian et al., 2014; Schwenter et
al., 2016; EI-Damanhoury and Gaintantzopoulou, 2018; Marcos et al., 2018).
Self-adhesive resin cement is a multi-functional product combining several functional
ingredients, such as silane and phosphate ester monomers, in one bottle. These
functional ingredients can chemically bond to different materials, including dentin,
enamel, ceramics, and metal, without additional pre-priming. Compared with
conventional resin cements, self-adhesive resin cements simplify the clinical steps and
show much lower technique sensitivity (Bähr et al., 2013). However, recent studies
found that pre-treatment with a silane coupling agent is needed to achieve a durable
adhesion, even if multi-purpose bonding products like self-adhesive resin cements
were used (Gré et al., 2016; Lee et al., 2017; Moro et al., 2017; Yao et al., 2017).One
aim of this study was to evaluate whether silanization would be affected by the
alternations of microstructure of lithium disilicate glass-ceramic caused by different
firing cycles; therefore, we designed these two popular bond strategies: including
combination of pre-silanization and using traditional or self-adhesive resin cements.
Consistent with the present results of surface roughness tests and SEM observation,
when adopting these two bond strategies, both resin bond strength and durability and
the bond failure modes of lithium disilicate glass-ceramic were not affected by the
number of ceramic firing cycles. Combined with the similar micro-mechanical
retention provided by HF etching, even when different numbers of firing cycles were
carried out, the indiscriminate bonding performance for these ceramics that received
different numbers of firing cycles suggested that multiple firing cycles, within four
times, cause no harm to chemical bonding of lithium disilicate glass-ceramics that
underwent silanization.
5. Conclusions
Based on the present study, and within its limitations, the following conclusions
may be drawn:
i. A complete heating schedule increased the fracture toughness of un-sintered
lithium disilicate glass-ceramic, which is essential for strengthening the physical
properties, but multiple firing cycles did not increase the fracture toughness
continuously.
ii. A complete heating schedule fulfilled crystallization of lithium disilicate
glass-ceramic, which also enhanced HF-acid resistance, but multiple firing cycles did
not change the HF-acid resistance.
iii. Heating decreased the surface hardness of un-sintered lithium disilicate.
However, up to four multiple firing cycles did not affect surface roughness and resin
bonding of lithium disilicate glass-ceramic.
Acknowledgements
This study was supported by the National Natural Science Foundation of China
[grant 81400539]; the National Key Research and Development Program of China
[2016YFA0201704], the Natural Science Foundation of Jiangsu Province [grants
BK20150998 and BK20140913], and the Jiangsu Higher Education Institutions
[grants 15KJB320003 and 2014-37].
Declarations of interest: none.
References
Addison O., Cao X., Sunnar P., Fleming G.J., 2012. Machining variability impacts on
the strength of a ‘chair-side’ CAD-CAM ceramic. Dent. Mater. 28, 880-887.
Alao A.R., Stoll R., Song X.F., Abbott J.R., Zhang Y., Abduo J., Yin L., 2017.
Fracture, roughness and phase transformation in CAD/CAM milling and
subsequent surface treatments of lithium metasilicate/disilicate glass-ceramics. J.
Mech. Behav. Biomed. Mater. 74, 251-260.
Bähr N., Keul C., Edelhoff D., Eichberger M., Roos M., Gernet W., Stawarczyk B.,
2013. Effect of different adhesives combined with two resin composite cements
on the shear bond strength to polymeric CAD/CAM materials. Dent. Mater. 32,
492-501.
Badawy R., EI-Mowafy O., Tam l.E., 2016. Fracture toughness of chairside
CAD/CAM materials-Alternative loading approach for compact tension test. Dent
Mater. 32, 847-852.
EI-Damanhoury H.M., Gaintantzopoulou M.D., 2018. Self-etching ceramic primer
versus hydrofluoric acid etching: Etching efficacy and bonding performance. J.
Prosthodont. Res. 62, 75-83.
Funda Bayindir and Ozlem Ozbayram; 2018. Effect of number of firings on the color
and translucency of ceramic core materials with veneer ceramic of different
thickness. J. Prosthet. Dent. 119, 152-158.
Guarda G.B., Correr A.B., Goncalves L.S., Costa A.R., Borges G.A., Sinhoreti M.A.,
Correr-Sobrinho L., 2013. Effects of surface treatments, thermocycling, and cyclic
loading on the bond strength of a resin cement bonded to a lithium disilicate glass
ceramic. Oper. Dent. 38, 208-217.
Gonuldas F., Yilmaz K., Ozturk C., 2014. The effect of repeated firings on the color
change and surface roughness of dental ceramics. J. Adv. Prosthodont. 6, 309-316.
Gré C.P., de Ré Silveira R.C., Shibata S., Lago C.T., Vieira L.C., 2016. Effect of
Silanization on Microtensile Bond Strength of Different Resin Cements to a
Lithium Disilicate Glass Ceramic. J. Contemp. Dent. Pract. 17, 149-153.
Hallmann L., Ulmer P., Kern M., 2018. Effect of microstructure on the mechanical
properties of lithium disilicate glass-ceramics. J. Mech. Behav. Biomed. Mater. 82,
355-370.
Hitz T., Stawarczyk B., Fischer J., Hämmerle C.H., Sailer I., 2012. Are self-adhesive
resin cements a valid alternative to conventional resin cements? A laboratory
study of the long-term bond strength. Dent. Mater. 28, 1183-1190.
Homaej E., Farhangdoost K., Tsoi J.K.H., Matinlinna J.P., Pow E.H.N., 2016. Static
and fatigue mechanical behavior of three dental CAD/CAM ceramics. J. Mech.
Behav. Biomed. Mater. 59, 304-313.
Jalali H., Bahrani Z., Zeighami S., 2016. Effect of Repeated Firings on Microtensile
Bond Strength of Bi-layered Lithium Disilicate Ceramics (e.max CAD and e.max
Press). J. Contemp. Dent. Pract. 17, 530-535.
Lung C.Y.K., Matinlinna J.P., 2012 Aspects of silane coupling agents and surface
conditioning in dentistry: an overview. Dent. Mater. 28, 467–477.
Lauvahutanon S., Takahashi H., Shiozawa M., Iwasaki N., Asakawa Y., Oki M.,
Finger W.J., Arksornnukit M., 2014. Mechanical properties of composite resin
blocks for CAD/CAM. Dent. Mater. 33, 705-710.
Li R.W., Chow T.W., Matinlinna J.P., 2014. Ceramic dental biomaterials and
CAD/CAM technology: state of art. J. Prosthodont. Res. 58, 208-216.
Lien W., Roberts H.W., Platt J.A., Vandewalle K.S., Hill T.J., Chu T.M., 2015.
Microstructural evolution and physical behavior of a lithium disilicate
glass-ceamic. Dent. Mater. 31, 928-40.
Lee H.Y., Han G.J., Chang J., Son H.H., 2017. Bonding of the silane containing
multi-mode universal adhesive for lithium disilicate ceramics. Restor. Dent.
Endod. 42, 95-104.
Moro A.F.V., Ramos A.B., Rocha G.M., Perez C.D.R., 2017. Effect of Prior silane
application on the bond strength of a universal adhesive to a lithium disilicate
ceramic. J. Prosthet. Dent. 118, 666-671.
Macros D.S.L., Flavia J.S.R.L., Adriana P.M., Jukka P.M., Ricardo M.C., 2018.
Innoviate Surface Treatments for Improved Ceramic Bonding: Lithium Disilicate
Glass Ceramic. Dent. Mater. 33, e95-e100.
Murillo-Gómez F., Palma-Dibb R.G., De Goes M.F., 2018. Effect of acid etching on
tridimensional microstructure of etchable CAD/CAM materials. Dent. Mater. 34,
944-955.
Özdemir H., Özdogan A., 2018. The effect of heat treatments applied to superstructure
porcelain on the mechanical properties and microstructure of lithium disilicate
glass ceramics. Dent. Mater. 37, 24-32.
Rifat Gozneli., Ender Kazazoglu., Yasemin Ozkan.,2014. Flexural properties of
leucite and lithium disilicate ceramic materials after repeated firing cycles. J. Dent.
Sci. 9, 144-150.
Serbena, F.C., Mathias, I., Foerster, C.E., Zanotto, E.D., 2015. Crystallization
toughening of a model glass-ceramic. Acta. Mater. 86, 216-228.
Schwenter J., Schmidli F., Weiger R., Fischer J., 2016. Adhesive bonding to polymer
infiltrated ceramic. Dent. Mater. 35, 796-802.
Sundfeld D., Correr-Sobrinho L., Pini N.I., Costa A.R., Sundfeld R.H., Pfeifer C.S.,
Martins L.R., 2016. The effect of Hydrofluoric Acid Concentration and Heat on
the Bonding to Lithium Disilicate Glass Ceramic. Braz. Dent. J. 27, 727-733.
Song X.F., Ren H.T., Yin L., 2016. Machinability of lithium disilicate glass ceramic in
vitro dental diamond bur adjusting process. J. Mech. Behav. Biomed. Mater. 53,
78-92.
Tang X., Nakamura T., Usami H., Wakabayashi K., Yatani H., 2012. Effects of
multiple firings on the mechanical properties and the microstructure of veneering
ceramics for zirconia frameworks. J. Dent. 40, 372-380.
Tang X., Tang C., Su H., Luo H., Nakamura T., Yatani H., 2014. The effects of
repeated heat-pressing on the mechanical properties and microstructure of IPS
e.max Press. J. Mech. Behav. Biomed. Mater. 40, 390-396.
Tian T., Tsoi J.K., Matinlinna J.P., Burrow M.F., 2014. Aspects of bonding between
resin luting cements and glass ceramic materials. Dent. Mater. 30, 147-162.
Wang R.R., Lu C.L., Wang G., Zhang D.S., 2013. Influence of cyclic loading on the
fracture toughness and load bearing capacities of all-ceramic crowns. Int. J. Oral.
Sci. 6, 99-104.
Yao C., Zhou L., Yang H., Wang Y., Sun H., Guo J., Huang C., 2017. Effect of silane
pretreatment on the immediate bonding of universal adhesives to computer-aided
design/computer-aided manufacturing lithium disilicate glass ceramics. Eur. J.
Oral. Sci. 125, 173-180.
Yuan K., Wang F., Gao J., Sun X., Deng Z., Wang H., Chen J., 2013. Effect of
sintering time on the microstructure, flexural strength and translucency of lithium
disilicate glass-ceramics. J. Non-Cryst. Solids. 362, 7-13.
Zhao T., Qin Y., Wang B., Yang J.F., 2015. Improved densification and properties of
pressureless-sintered lithium disilicate glass-ceramics. Mater. Sci. Eng. A. 620,
399-406.
Zhang P., Li X.H., Yang J.F., Xu S.C., 2014. The crystallization and microstructure
evolution of lithium disilicate-based glass-ceramic. Journal of Non-Crystalline
Solids. 392-393, 26-30.
Tables
Table 1. Weibull statistics determining a 10% probability of fracture ((10) ) derived
from fracture toughness values.
Groups
() ()
Scale parameter, σθ (MPa)
M
0
3.565
3.496
5.107
1
6.720
6.652
9.933
2
5.305
5.246
9.003
3
5.311
5.248
8.322
4
5.229
5.170
8.829
Table 2. SBS strength values obtained from 24-h or 120-d water storage for each
group.
Groups
SBS (MPa)/(24 h)
Mean±SD
Confidence
SBS (MPa)/(120 d)
Mean±SD
Confidence
interval
interval
(95%)
(95%)
1-RV
9.79 ± 1.16
9.14–10.43
9.78 ± 1.05a
9.19–10.37
1-RU
9.71 ± 1.00
9.42–10.53
9.67 ± 1.03a
9.10–10.24
2-RV
10.13 ± 1.24
9.44–10.81
9.63 ± 1.05a
9.05–10.21
2-RU
10.54 ± 1.01
9.98–11.09
10.00 ± 0.97a
9.46–10.54
3-RV
9.98 ± 1.00
9.43–10.53
9.92 ± 0.89a
9.42–10.41
3-RU
10.55 ± 1.15
9.91–11.18
9.83 ± 1.02a
9.26–10.39
4-RV
10.19 ± 1.16
9.55–10.83
9.74 ± 1.05a
9.17–10.45
4-RU
10.07 ± 1.03
9.51–10.65
9.86 ± 1.04a
9.29–10.44
Values with the same superscript letters are not significantly different (p<0.05).
Table 3. Surface roughness means and standard-deviation values of lithium disilicate
glass-ceramic specimens that received zero to four firing cycles with or without HF
etching.
Group
s
Surface roughness (μm)/polished
Mean±SD
Confidence
Surface roughness (μm)/HF-etched
Mean±SD
interval (95%)
Confidence
interval (95%)
0
0.038 ± 0.007a
0.021–0.055
0.580 ± 0.077b
0.389–0.771
1
0.038 ± 0.007a
0.020–0.056
0.516 ± 0.099b
0.271–0.761
2
0.032 ± 0.003a
0.025–0.040
0.483 ± 0.092b
0.460–0.506
3
0.034 ± 0.003a
−0.020–0.089
0.437 ± 0.138b
0.956–0.779
4
0.026 ± 0.003a
0.023–0.029
0.444 ± 0.078
0.251-0.637
Values with the same superscript letters are not significantly different (p<0.05).
Figures and figure legends
Fig. 1. Mean and Standard Deviation of surface hardness values. Different labels (a–b)
represent group means that were significantly different (p<0.05).
Fig. 2. Mean and standard deviation of fracture toughness values. Different labels (a–
c) represent group means that were significantly different (p<0.05).
Fig. 3. Weibull plots for all experimental groups with 95% confidence interval.
Fig. 4. Failure modes observed in all groups of SBS tests after 24 h and 120 d of
storage in distilled water at 37°C: Adhesive, failure at the ceramic surface; mixed,
combination of adhesive failure at ceramic surface; and cohesive failure in luting resin
or composite cylinder.
Fig. 5. Representative images showing the different roughnesses of lithium disilicate
glass-ceramic receiving zero to four firing cycles with (a–e) and without HF etching
(A–E).
Fig. 6. Typical SEM images (5000× magnification) of polished (A–E) and HF-etched
(a–e) lithium disilicate glass-ceramic receiving different numbers of firing cycles.
Labels A–E and a–e represent zero to four firing cycles.
Highlights

Up to four multiple firing cycles partly affected the mechanical properties of
lithium disilicate glass-ceramic.

A complete heating schedule enhanced HF-acid resistance of partially crystallized
lithium disilicate glass-ceramic, but multiple firing cycles did not change the
HF-acid resistance.

Up to four multiple firing cycles did not affect surface roughness and resin
bonding of lithium disilicate glass-ceramic.
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