Influence of restoration thickness and dental bonding surface on the fracture resistance of full-coverage occlusal veneers made from lithium disilicate ceramic.

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DENTAL-2557; No. of Pages 9

d e n t a l m a t e r i a l s x x x ( 2 0 1 5 ) xxx–xxx

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Influence of restoration thickness and dental bonding surface on the fracture resistance of full-coverage occlusal veneers made from lithium disilicate ceramic Martin Sasse ∗ , Anna Krummel, Karsten Klosa, Matthias Kern Department of Prosthodontics, Propaedeutics and Dental Materials, School of Dentistry, Christian-Albrechts University, Arnold-Heller-Str. 16, 24105 Kiel, Germany

a r t i c l e

i n f o

a b s t r a c t

Article history:

Objectives. The purpose of this in-vitro study was to evaluate the influence of ceramic

Received 9 September 2014

thickness and type of dental bonding surface on the fracture resistance of non-retentive

Received in revised form

full-coverage adhesively retained occlusal veneers made from lithium disilicate ceramic.

4 March 2015

Methods. Seventy-two extracted molars were divided into three test groups (N = 24) depend-

Accepted 28 April 2015

ing on the location of the occlusal veneer preparation: solely within enamel, within enamel

Available online xxx

and dentin or within enamel and an occlusal composite resin filling. For each test group,

Keywords:

e.max CAD) in three subgroups with different thicknesses ranging from 0.3 to 0.7 mm in the

Fracture resistance

fissures and from 0.6 to 1.0 mm at the cusps. The veneers were etched (5% HF), silanated

Ceramic thickness

and adhesively luted using a self etching primer and a composite luting resin (Multilink

Dental bonding surface

Primer A/B and Multilink Automix). After water storage at 37 ◦ C for 3 days and thermal

Full-coverage molar restoration

cycling for 7500 cycles at 5–55 ◦ C, specimens were subjected to dynamic loading in a chewing

occlusal all-ceramic restorations were fabricated from lithium disilicate ceramic blocks (IPS

All-ceramic

simulator with 600,000 loading cycles at 10 kg combined with thermal cycling. Unfractured

Self etching primer

specimens were loaded until fracture using a universal testing machine. Statistical analysis was performed using Kruskal–Wallis and Wilcoxon tests with Bonferroni–Holm correction for multiple testing. Results. Only specimens in the group with the thickest dimension (0.7 mm in fissure, 1.0 mm at cusp) survived cyclic loading without any damage. Survival rates in the remaining subgroups ranged from 50 to 100% for surviving with some damage and from 12.5 to 75% for surviving without any damage. Medians of final fracture resistance ranged from 610 to 3390 N. In groups with smaller ceramic thickness, luting to dentin or composite provided statistically significant (p ≤ 0.05) higher fracture resistance than luting to enamel only. The thickness of the occlual ceramic veneers had a statistically significant (p ≤ 0.05) influence on fracture resistance. Significance. The results suggest to use a thickness of 0.7–1 mm for non-retentive fullcoverage adhesively retained occlusal lithium disilicate ceramic restorations. © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

∗

Corresponding author. Tel.: +49 431 597 2874; fax: +49 431 597 2860. E-mail address: [email protected] (M. Sasse).

http://dx.doi.org/10.1016/j.dental.2015.04.017 0109-5641/© 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Please cite this article in press as: Sasse M, et al. Influence of restoration thickness and dental bonding surface on the fracture resistance of full-coverage occlusal veneers made from lithium disilicate ceramic. Dent Mater (2015), http://dx.doi.org/10.1016/j.dental.2015.04.017


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1.

Introduction

The prosthodontic treatment of severly abraded teeth or patients with a lateral open bite after orthodontic treatment is an important aspect in dental therapy. Modern dental ceramics such as lithium disilicate nowadays offer the option of minimally invasive replacement of lost tooth substance [1] while having a high fracture resistance [2,3]. Failures of allceramic restorations are mainly based on fractures of the ceramic material [3–6]. Fracture resistance of all-ceramic restorations is influenced by different factors. The adhesive technique used plays an important role in this regard since adhesively bonded all-ceramic restorations show a higher fracture resistance than conventionally cemented restorations [7–14]. Today resin cements based on the Bisphenol A glycidylmethacrylate compound are being used primarily. In order to bond to the surfaces of the different components (tooth structure as well as restoration) they need to be conditioned specifically; since each interface quality influences the fracture resistance of the restoration [2,7]. The type of bonding surface and the type of surface conditioning affects the bond strength of the ceramic to the tooth structure. Restorations bonded to teeth using the total etch technique achieved a bond strength of up to 28 MPa [15] within the enamel and 13 to 20 MPa within the dentin (depending on the adhesive system used) [16,17]. An improved bond strength to dentin can be reached when an immediate sealing of the dentin after the preparation is done [18]. Today many manufacturers offer self-etching primers which are supposed to simplify the adhesive bonding procedure. Different bond strength values have been reported in the literature regarding these self-etching primers. The bond strength of ceramic bonded to enamel was about 26 MPa regardless of the manufacturer while the bond strength of ceramic bonded to dentin was 15 to 29 MPa depending on the adhesive system used [17,19,20]. In these studies specimens were not subjected to thermal cycling, water storage or masticatory simulation though. For example a study of Zhang et al. [21] reported a bond strength to dentin of up to 36 MPa using a self-etching primer. A further factor influencing the fracture resistance of allceramic restorations is the design of the preparation. For all-ceramic restorations the preparation has to be rounded carefully and no sharp angles should exist [4,22–25]. The thickness of the ceramic restoration is another factor influencing its fracture resistance [26]. Scientific data on the minimum thickness of lithium disilicate ceramic partial crowns or occlusal veneers is rare. In vitro studies on bonded occlusal veneers made of emax CAD showed that restorations with a thickness of 1.2–1.8 mm withstood forces of up to 1000 N and thicknesses of 0.6–1.0 mm withstood 800 N [27,28]. A study of Guess et al. [29] investigated the influence of the thickness and the extension of different premolar partial crowns made of a pressed lithium disilicate ceramic. No significant effect on the fracture resistance of pressable lithium disilicate ceramic onlay restorations was found in this study when the preparation depth was reduced down to 0.5 mm.

The success of all-ceramic restorations is related to multiple factors. The purpose of this study was to evaluate the effect of varying thicknesses of non-retentive full-coverage adhesively retained occlusal lithium disilicate ceramic restorations (further on referred to as occlusal veneers) bonded to different surfaces using a bonding system based on a self-etching primer.

2.

Materials and methods

2.1.

Specimen fabrication

Seventy two human molars without any caries or fillings were cleaned and stored in a 0.1% thymol solution. They were embedded in a technique which proved to be effective in previous studies [2,30–32]. The root portion apically of the cemento-enamel junction was coated with an artificial periodontal membrane made of gum resin (Anti-RutschLack, Wenko-Wenselaar, Hilden, Germany). The roots of the teeth were then embedded in custom made standard brass cylinders (Ø 15 mm) positioned along their long axis with autopolymerizing acrylic resin material (Technovit 4000, Heraeus Kulzer, Wehrheim, Germany). The enamel-cement junction was located 2 mm above the level of the embedded resin. The roots were retained in the resin by a thin steel bar (Ø 0.9 mm) inserted in the apical third of the root. Specimens were divided into three groups (n = 24 each). In the first group the preparation was only within the enamel (group EN), in the second group the preparation was not limited to the enamel but extended into the dentin (group ED) and in the third group the preparation extended into the dentin also but the dentin core was reduced by 1.5 mm and a composite filling (Tetric EvoCeram, Ivoclar Vivadent, Schaan, Liechtenstein) was placed into the cavity (group EC) using a three-step bonding system (Optibond FL, Kerr, Charlotte, NC, USA). Finally all preparations and all composite fillings were smoothed and sharp edges were rounded. In all three groups the circumferential outline of the preparation was strictly within the enamel. An angle of 150 degrees was prepared between the cusps (Fig. 1). After tooth preparation, impressions were made using a simultaneous dual-mix technique with polyether material (Permadyne Penta H und L, 3 M ESPE, Seefeld, Germany). The impressions were cast with die stone type 4 (Hydrobase300, Dentona, Dortmund, Germany). The teeth were stored in a 0.1% thymol solution until adhesive luting. In order to achieve a constant ceramic thickness the occlusal surface received a semi-anatomic shaping. In the CAD/CAM software the occlusal surface of the tooth was virtually elevated and then reduced again in the fissure area until the desired thickness was obtained. The master casts were sent to a commercial milling center (Biodentis, Leipzig, Germany). The unsintered ceramic occlusal veneers were then milled out of lithium disilicate blocks (IPS e.max.CAD, Ivoclar Vivadent, Schaan, Liechtenstein) in accordance to the planned design using CAD/CAM technique. They were fitted to the master casts and sintered according to the manufacturers’ directions. Test groups are summarized in Table 1.



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Fig. 1 – Preparation design of the test groups (E = enamel, D = dentin, C = composite resin filling).

2.2.

Bonding procedure

A self-etching primer (Multilink Primer A and B, Ivoclar Vivadent, Schaan, Liechtenstein) was mixed for 10 s with a ratio of 1:1. The teeth were then pretreated according to the following protocol: in groups EN and EC the primer was applied onto the bonding surface of the tooth with a brush for 15 s and after another 15 s the surface was gently air dried. In group ED the primer was first applied to the enamel surface for 15 s before it was applied to the dentin surface for 15 s, followed by gentle air drying of the surface. The bonding surfaces of the restorations were etched for 20 s using 5% hydrofluoric acid etching gel (IPS Ceramic Ätzgel, Ivoclar Vivadent). The etched ceramic surface was thoroughly cleaned using water spray for 60 s. After airdrying a silane coupling agent (Monobond Plus, Ivoclar Vivadent) was applied and air dried again after 60 s. A self-curing luting composite (Multilink Automix, Ivoclar Vivadent) was dispensed from the automix syringe onto the bonding surface of the restoration and onto the fissure area of the tooth. The restoration was positioned by hand and kept in place by a special loading apparatus with a constant force of 50 N. Subsequently, all margins were light-cured for 20 s according to the manufacturer’s instructions. After a curing period of 5 min the specimens were removed from the loading apparatus, the margins were polished and the specimens were stored in water for 3 days at 37 ◦ C in order to achieve complete curing.

2.3.

Cyclic loading and fracture load

After water storage all specimens were first thermocycled 7500 times between 5 and 55 ◦ C in tap water with a 30 s dwell time

at each temperature in a computerized masticatory simulator (Willytec, Munich, Germany), followed by combined thermocycling (60 s dwell time) and dynamic loading for another 600,000 cycles with a weight of 10 kg. A loading cycle frequency of 2.0 Hz with a lateral sliding component of 0.3 mm towards the central fissure was chosen to simulate conditions in the oral cavity. The descending velocity was 30 mm/s, the ascending velocity was 55 mm/s and the vertical motion was 6 mm. The antagonistic tooth was simulated by a steatite ceramic ball 5 mm in diameter (Hoechst Ceram Tec, Wunsiedel, Germany) which was positioned so that it first contacted the supporting cusp when moving down. Following masticatory simulation all unfractured specimens were examined using a stereomicroscope (Wild, Heerbrugg, Switzerland) and they were photographed (Leica DC 100, Leica Microsystems, Cambridge, UK) in order to record possible damage. The specimens were then loaded until fracture in a universal testing machine (Zwick Z010/TN2A, Ulm, Germany). A steel bar with a 6 mm ball end was centered on the main fissure of each specimen in order to apply the load evenly to the triangular ridges of the oral and buccal cusps. Additionally a 0.6 mm tin foil was placed between the ball end and the specimen in order to distribute the load homogenously. The steel bar descended at a cross-head speed of 2 mm/min while a computer software (testXpert II, Zwick, Ulm, Germany) recorded the maximum load until fracture in Newton. After static loading all specimens underwent a stereomicroscopic evaluation again and were photographed. In addition sampled fragments of specimens that did not withstand dynamic loading as well as sampled fragments of specimens after static loading were evaluated using a scanning electron microscope (XL 30 CP, Philips, Eindhoven,

Table 1 – Allocation of test groups. Preparation (group code)

Restricted to enamel (EN) (n = 24) Enamel and dentin (ED) (n = 24) Enamel and dentin with composite filling (EC) (n = 24)

Ceramic thickness 0.3–0.6 mm (n = 24)

0.5–0.8 mm (n = 24)

0.7–1.0 mm (n = 24)

EN1 (n = 8) ED1 (n = 8) EC1 (n = 8)

EN2 (n = 8) ED2 (n = 8) EC2 (n = 8)

EN3 (n = 8) ED3 (n = 8) EC3 (n = 8)



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Fig. 2 – Overview and SEM image at ×50 magnification of the occlusal surface of a restoration showing micro crack formation after dynamic loading.

Netherlands) in order to gain information on the failure mode of the adhesive bond. Some specimens which already showed damage after dynamic loading were also inspected using the scanning electron microscope.

2.4.

Analysis of results and statistics

The Shapiro–Wilk test was performed on all groups and revealed, that some groups were not distributed normally. Hence the Kruskal–Wallis test was performed on all groups and revealed statistically significant differences. This test was followed by multi-pairwise comparisons of all groups using the Wilcoxon rank sum test and the risk of an alpha error was reduced by performing the procedure of Bonferroni–Holm on each resulting p-value.

3.

Results

Some specimens did not withstand dynamic loading unscathed. They were rated as failure when chippings occurred. As partial failure they were rated when crack formation took place (Fig. 2) and specimens were rated as a success when they did not show any macroscopic damage after masticatory simulation. The results regarding survival after dynamic loading are shown in Table 2 and the results for median loads until fracture of the different groups are shown in Table 3. Statistical analysis of the data regarding thickness of the restorations showed statistically significant differences when comparing groups EC1 and EC3 (p = 0.01041) as well as when comparing groups EC2 and EC3 (p = 0.00193). Regarding the different bonding surfaces statistically significant differences could be found within grouping factor 1 when testing groups EN1 vs ED1 (p = 0.005253) and groups EN1 vs EC1 (p = 0.002567). Within grouping factor 3 statistically significant differences could be found when testing groups EN3 vs ED3 (p = 0.006993) and EN3 vs EC3 (p = 0.0001554). So for grouping factor 1 and 3 luting on dentin or composite provided statistically significant higher fracture resistance values than luting on enamel.

Stereomacroscopic and scanning electron microscopic evaluation of the fractured surfaces within group EN (preparation restricted to enamel) showed a failure of the adhesive interface between the enamel surface and the luting composite (Fig. 3). Within group ED (preparation extended into the dentin) failure of the adhesive interface occurred between the restoration surface and the luting composite as well as in the adhesive interface of the hybrid layer (Figs. 4 and 5). Within group EC the fractures occurred at the adhesive interface between the restoration surface and the luting composite (Fig. 6).

4.

Discussion

The influence of the thickness of non-retentive full-coverage adhesively retained occlusal ceramic veneers on their fracture resistance and the influence of the underlying bonding substrate were evaluated in this study. For this study the design of the preparation was chosen based on a study of Clausen et al. [2] and based on general preparation guidelines [25,33]. Specimens were thermal cycled in order to simulate the physical stress dental restorations are exposed in the oral cavity. Thermocycling stress and tensions occur at

Table 2 – Survival rates for dynamic loading including partial failures (A) and regarding complication-free restorations only (B). Ceramic thickness (mm)

Survival rates (%) A

B

EN

0.3–0.6 0.5–0.7 0.7–1.0

50 75 100

50 75 100

ED

0.3–0.6 0.5–0.7 0.7–1.0

100 50 100

50 50 100

EC

0.3–0.6 0.5–0.7 0.7–1.0

100 100 100

12.5 37.5 100


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Table 3 – Median fracture resistance (N) of groups, minima, maxima for static loading and influence of the ceramic thickness and the bonding substrate. Medians with the same upper case superscript letter within the same row (=different thicknesses) are not statistically different (p > 0.05). Medians with the same lower case subscript letter within the same column (=different bonding substrate) are not statistically different (p > 0.05). Preparation (group code)

Thickness 0.3–0.6 mm (n = 24) A

0.5–0.8 mm (n = 24) A

0.7–1.0 mm (n = 24)

Restricted to enamel (EN) (n = 24)

Med Min Max

610 a 0 2230

2355 a 0 3170

2070A a 1450 2570

Enamel and dentin (ED) (n = 24)

Med Min Max

2370A b 1530 2700

1105A a 0 3800

3000A b 1880 3780

Enamel and dentin with composite filling (EC) n = 24

Med Min Max

2765A b 1400 3940

2270A a 1520 3000

3390B b 2860 4080

Fig. 3 – Overview of a sample of group EN after static loading showing no visible composite leftovers on the tooth surface and SEM image of the basal surface of a chipped fragment at ×50 magnification. It shows a homogenous surface of the luting composite mirroring the grinded tooth surface.

Fig. 4 – Overview and stereomicroscopic view at ×8 magnification of a sample of group ED. No visible composite leftovers can be found on the enamel surface (E) while partial leftovers can be found on the dentin surface (D).



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Fig. 5 – SEM images of another sample of group ED. View on the basal surface of a chipped fragment at ×50, ×125 and ×2000 magnification. Areas of different underlying tooth substance can be distinguished (D-dentin, E-enamel, T-transition zone). A distinct shift in surface structure can be found within the transition zone at ×2000 magnification. In the lower part (enamel zone) composite leftovers indicate a failure in between the enamel and the luting composite and in the upper part (dentin zone) a failure within the hybrid layer is indicated by the ripped out areas of the dentinal tubules.

the adhesive interface due to the different thermal expansion coefficients of the materials [34], which affect the bond strength. The intent of the thermocycling process before dynamic loading in combination with thermocycling was to artificially preage the specimen with an increased frequency of thermocycling even before mechanical loading. During thermocycling without mechanical loading, the specimen was thermal cycled between 5 and 55 ◦ C in tap water with a 30 s dwell time at each temperature and a 6 s switch time. While during cyclic loading, the specimen was thermal cycled with a 60 s dwell time and a 15 s switch time. Further on specimens were dynamically loaded in order to simulate the mechanical stress while chewing as well. According to a previous study [2] specimens were loaded with a force of 10 kg and an additional lateral sliding movement of 0.3 mm was applied to simulate the sliding movement of the antagonistic tooth while chewing [2,30]. The number of cycles in the masticatory simulator was set to 600,000 as in previous studies [2,30,32] which equals a clinical use of 2.5 years [35,36]. Specimens that did not fracture during dynamic loading were quasi-static loaded until

fracture as in previous studies [2,30,32] again. Analog to clinical studies [37–40] and one in vitro study [41] all restorations that did not show a loss of function were regarded as success or partial success even if crack formation took place. Specimens that fractured or showed chippings were regarded as failure and selected fragments were analyzed concerning the type of failure. The statistical analysis revealed that a thickness of the ceramic restoration of 0.7–1 mm lead to a significant higher fracture resistance compared to thinner restorations within the group bonded to enamel and composite filling (EC). In the two remaining groups no significant influence of the thickness could be shown. When analyzing the results, the survival rate of the dynamic loading should not be neglected though. In all three groups only the restorations with a thickness of 0.7–1 mm completely withstood the dynamic loading unharmed. Regarding the partial success rate (restorations with crack formation included) all restorations in the group bonded to enamel and composite filling (EC) and in the group bonded to enamel and dentin (ED) except the ones with a thickness of 0.5–0.8 mm withstood the dynamic loading complete.




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Fig. 6 – Overview, stereomicroscopic view at ×8 and at ×50 magnification of samples of group EC. Clearly recognizable leftovers can be found on the surface of the composite filling (C) while no luting composite leftovers can be found on the enamel surface (E). On the basal surface of the chipped fragment areas of different underlying tooth substance can be distinguished (C-composite filling, E-enamel, T-transition zone). Clearly visible is the definite shift in surface structure from the enamel zone to the zone of the underlying composite filling where no leftovers of the luting composite can be found on the ceramic restorations surface.

A prediction on the remaining longevity of such restorations already showing crack formation, cannot be made since no studies on this subject have been published so far. It has to be noted that the lowest values of fracture resistance within any group did not necessarily occur at restorations with cracks present. The statistical analysis of the groups with a thickness of 0.3–0.6 mm and 0.7–1.0 mm concerning the influence of the bonding surface on the fracture resistance revealed a significant difference comparing the enamel bonded restorations (EN) to the dentin (ED) and composite resin filling (EC) bonded restorations with the loading values until fracture being lower for the enamel bonded restorations than for the other two groups. The values measured in group EN3 ranged from 1450 to 2570 N and thereby exceeded the recommended minimum fracture strength for posterior restorations of 500–700 N [42] by far. The fracture resistance observed for these restorations was in the same range as for untreated human molars [41,43]. A thickness of 0.7–1.0 mm can therefore be recommended for clinical use, since in this group neither a failure nor a partial failure occurred. The restorations that were bonded solely to enamel showed inferior results which is in contradiction to the results of other studies [41,44] in which the bond strength of luting composite was investigated and also to results of studies [2,7,45,46] in which the fracture resistance of restorations either bonded to enamel or dentin was investigated. The assumed reason for

this difference is the utilized adhesive luting system applied to the tooth surfaces. In the studies mentioned above, the tooth surfaces were conditioned using the total-etch technique while in the current study a self-etching primer only was used for conditioning of the tooth surfaces. The significantly higher fracture resistance when bonding to dentin in the current study is in accordance to a study of Zhang et al. [21]. They found that regarding the bond strength to dentin, conditioning with a self-etching primer lead to higher bond strength values as compared to the totaletch technique. A further option for the improvement of the bond strength to dentin is the immediate dentin sealing technique as described by Magne et al. [18]. Another study on the marginal quality of restorations bonded to enamel and dentin found a significantly decreased marginal quality after masticatory simulation for specimen bonded to enamel using a self-etching primer [47]. This again is in accordance to the current study. The highest values of fracture resistance and the highest survival rates in our study were found with restorations which were partly bonded to composite fillings. Few studies were found regarding the bond strength of composite fillings to the luting resin and the ceramic restoration in dependence of the applied surface conditioning method. A study of Sabatini et al. [48] investigated the shear bond strength of luting resins to various prosthodontic substrates. They found that the bond strength values of Multilink Automix to composite fillings using A/B primer achieved 32 MPa which is in the



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same range as the bond strength to dentin found in one other study [21]. There is a major difference though to other studies investigating the bond strength of Multilink Automix to dentin [49–51]. In these studies bond strength values in the range of 18.5 MPa or even lower were reported. Since some of these studies involved thermocycling and artificial aging while others did not, comparisms to other studies are difficult due to the different designs of the studies. This also explains the wide range of the resulting values. Comparing the current results to other studies on the fracture resistance of lithium disilicate restorations it is noticeable that the values of fracture resistance were significantly higher than in a similar study of Guess et al. [29]. In their work they evaluated the relationship of the design and extension of the preparation and the thickness of occlusal veneers made of a pressed lithium disilicate ceramic bonded to human premolars. No influence on the fracture resistance was found in that study when comparing pressable lithium disilicate ceramic onlay restorations with different occlusal thicknesses. The preparation design used in that study was different to the one used in our study though and the specimen were bonded using the total-etch technique. However, the results of the above study [29] suggest that within our study the group bonded solely to enamel would have shown better results when the total-etch technique would have been choosen as conditioning method for the enamel. Overall the fracture resistance values achieved in the study of Guess et al. [29] were in a lower range (median 729–1300 N) than in our study (median 610–3390 N) which might be due to the different type of teeth that were restored (premolars vs molars) and to the different preparation designs used. In addition the results suggest to conduct a followup study to evaluate wether the fracture resistance and the survival rate will increase when the total-etch technique is used as pretreatment of the enamel. This follow-up study would also clarify wether even further decreased thicknesses of the occlusal veneers might be recommended for clinical use. In a study of Yildiz et al. [52] the fracture resistance of pressed and CAD/CAM manufactured lithium disilicate partial crowns with an occlusal thickness of 1.5 mm (according to the manufacturer’s recommendation) was compared and a lower fracture resistance for the CAD/CAM restorations was revealed. They also investigated the influence of the bonding technique on the fracture resistance by bonding some specimen using the total-etch technique and the others by using Multilink primer A/B as conditioning method. Specimens conditioned with Multilink primer showed a significantly lower fracture resistance than specimens conditioned with the totaletch technique. The overall values of fracture resistance were again lower (1584 ± 238 MPa) as compared to our study. Again this might also be due to a different preparation and study design.

5.

Conclusion

The results of the current study support the treatment of occlusal abrasion or malpositioned teeth with non-retentive lithium disilicate ceramic occlusal veneers.

They suggest that a minimum thickness of 0.7–1.0 mm should not be deceeded when a self-etching primer is used for conditioning of the tooth substrate.

Acknowledgement The authors gratefully acknowledge the support of this study by Ivoclar-Vivadent, Schaan, Liechtenstein, by providing their materials free of charge, as well as by Absolute Ceramics, Biodentis GmbH, Leipzig, Germany, by manufacturing the restorations free of charge.

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Esthetic rehabilitation with laminated ceramic veneers reinforced by lithium disilicate.

Influence of ceramic thickness and ceramic materials on fracture resistance of posterior partial coverage restorations.

Surface characterization of lithium disilicate ceramic after nonthermal plasma treatment.

Digital workflow for virtually designing and milling ceramic lithium disilicate veneers: a clinical report.

In vitro study of the fracture resistance of monolithic lithium disilicate, monolithic zirconia, and lithium disilicate pressed on zirconia for three-unit fixed dental prostheses.

Improving the fracture resistance of dental ceramic.

Effect on in vitro fracture resistance of the technique used to attach lithium disilicate ceramic veneer to zirconia frameworks.

CAM composite and composite-ceramic occlusal veneers.

Influence of veneer and cyclic loading on failure behavior of lithium disilicate glass-ceramic molar crowns.

Evaluation of adhesive bonding of lithium disilicate ceramic material with duel cured resin luting agents.

Effect of core ceramic grinding on fracture behaviour of bilayered lithium disilicate glass-ceramic under two loading schemes.

Cement luting thickness beneath porcelain veneers made on platinum foil.

Wear behavior of pressable lithium disilicate glass ceramic.

Influence of ceramic thickness and type on micromechanical properties of light-cured adhesive bonding agents.

Effect of surface pretreatments on the microtensile bond strength of lithium-disilicate ceramic repaired with composite resin.

Effect of adhesive luting on the fracture resistance of zirconia compared to that of composite resin and lithium disilicate glass ceramic.

Enamel and Dentin Surface Finishing Influence on the Roughness and Microshear Bond Strength of a Lithium Silicate Glass-Ceramic for Laminate Veneers.

Do surface treatments affect the optical properties of ceramic veneers?

Effect of prophylactic polishing pastes on roughness and translucency of lithium disilicate ceramic.

Effect of Different Luting Agents on the Retention of Lithium Disilicate Ceramic Crowns.

Influence of resin cement shade on the color and translucency of ceramic veneers.

Survival of anterior cantilevered all-ceramic resin-bonded fixed dental prostheses made from zirconia ceramic.

Replacement of missing lateral incisors with lithium disilicate glass-ceramic veneer-fixed dental prostheses: a clinical report.

The influence of resin cements on the final color of ceramic veneers.