Influence of bonding surface and bonding methods on the fracture resistance and survival rate of full-coverage occlusal veneers made from lithium disilicate ceramic after cyclic loading

Surface roughness, wear, and abrasiveness of printed and milled occlusal veneers after thermomechanical aging

STATEMENT OF PROBLEM

Occlusal veneers are a conservative method of reestablishing vertical dimensions of occlusion (VDO) for worn teeth. A restorative material used for occlusal veneers should have a smooth surface, adequate wear resistance, and low abrasiveness to the antagonists, as total wear of occlusal veneers and their antagonists determines the stability of the reestablished VDO. Studies on roughness, wear, and abrasiveness of occlusal veneers are scarce.

PURPOSE

The purpose of this in vitro study was to assess the surface roughness, wear, and abrasiveness of printed and milled occlusal veneers after thermomechanical aging against natural cusps and restorative materials.

MATERIAL AND METHODS

Forty-eight extracted mandibular first molars were prepared for occlusal veneers and scanned with an intraoral scanner. The scans were exported to a computer-aided design program to design the occlusal veneers in 3 groups (n=16) according to the restorative material: group IP: milled lithium disilicate; group EN: milled hybrid ceramic (Vita Enamic), group VA: printed hybrid ceramic (Varseosmile Crown plus). The occlusal veneers in each group were bonded to their corresponding abutments and subjected to 250 000 mechanical cycles and a simultaneous 1000 thermal cycles in a mastication simulator. During thermomechanical aging, half of the specimens of each study group (n=8) were opposed by natural cusps (antagonist C) and the other half by antagonist cusps fabricated from the same restorative material as the occlusal veneers (antagonist R). The wear of the occlusal veneers and their antagonists was assessed with a 3-dimensional processing software program. The surface roughness of the veneers was assessed with a contact profilometer. The results were statistically analyzed with a 2-way ANOVA followed by the post hoc Tukey HSD test (α=.05).

RESULTS

The 2-way ANOVA indicated a significant effect for the material and the antagonist on surface roughness, wear, and abrasiveness (P<.05). When opposed by antagonist C, VA showed significantly higher surface roughness than IP and EN (P<.001). VA had significantly higher surface wear followed by EN and IP (P<.001). IP caused significantly higher wear to antagonist C than EN and VA (P<.001). In addition, IP had significantly higher total wear (combined wear of veneers and their antagonists) followed by VA and EN (P<.001). When opposed by antagonist R, no significant difference was found among the 3 materials for surface roughness (P=.08), material wear (P=.12), opposing wear (P=.11), or total wear (P=.11).

CONCLUSIONS

Both material and antagonist had a significant effect on surface roughness and occlusal stability when occlusal veneers were fabricated to restore VDO. VA had significantly more surface roughness and wear than EN and IP when opposed by natural cusps. IP abraded natural cusps significantly more than EN and VA. The 3 tested materials showed similar roughness, wear, and abrasiveness when opposed by the same material.

Laser debonding of ultrathin occlusal veneers fabricated from different CAD/CAM ceramic materials

BACKGROUND

Erbium lasers safely offer the possibility of reuse for debonded restorations. Since these lasers have a high affinity for water molecules, they are absorbed by resin cement causing explosive ablation of the cement and thus, the restoration debonds. The efficiency of this process depends on many factors, including the ceramic type, its chemical composition and thickness. Therefore, this study was designed to test the time taken to debond ultrathin occlusal veneers made of three types of milled ceramic materials and evaluate the integrity of these restorations after debonding.

METHODS

Three ceramic types were evaluated in this study: lithium disilicate (IPS Emax CAD), highly condensed lithium disilicate (GC initial®LiSi), and translucent zirconia (Katana zirconia STML). Each group consisted of 8 occlusal veneers of 0.5 mm thickness. The samples were cemented to the occlusal surfaces of the upper molar teeth. An Er; Cr: YSGG laser was applied to the occlusal veneers using the scanning method, and time until debonding was calculated. The debonded samples were then inspected under a stereomicroscope for possible damage. Numerical data are presented as the mean with 95% confidence interval (CI), standard deviation (SD), minimum (min.) and maximum (max.) values. Normality and variance homogeneity assumptions were confirmed using Shapiro-Wilk's and Levene's tests, respectively. Data were normally distributed and were analyzed using one-way ANOVA followed by Tukey's post hoc test. The significance level was set at p < 0.05 for all tests. Statistical analysis was performed with R statistical analysis software version 4.3.2 for Windows (R Core Team (2023). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL https://www.R-project.org/).

RESULTS

There was no significant difference in debonding time between the different materials (p = 0.995). The longest debonding time was found for Katana STML (87.52 ± 20.45) (seconds), followed by Emax (86.94 ± 20.63) (seconds), while the lowest value was found for LiSi initial (86.14 ± 25.16) (seconds). In terms of damage to the debonded veneers, The Emax and zirconia samples showed no damage. However, 40% of the LiSi samples fractured during debonding, and 20% exhibited cracks. Only 40% of the LiSi samples were sound after debonding.

CONCLUSION

Er; Cr: YSGG laser can be used efficiently to remove ceramic occlusal veneers. However, its effect on LiSi restorations needs further research.

Fracture resistance of chairside CAD-CAM lithium disilicate occlusal veneer with various designs after mechanical aging

PURPOSE

This study evaluated the fracture resistance of chairside computer-aided design and computer-aided manufacturing (CAD-CAM) lithium disilicate crown, onlay, and non-anatomical occlusal veneer (A-OV) with and without margin fabricated.

MATERIALS AND METHODS

Sixty-four CAD-CAM lithium disilicate restorations were designed as (1) complete coverage crown (CCC); (2) A-OV with margin; (3) non-A-OV with margin (NA-OV-M); and (4) non-A-OV without margin (NA-OV-NM), 16 of each. Restorations were crystallized and adhesively luted to resin dies using resin cement. Specimens were then subjected to 400,000 cycles of chewing in a mastication simulator. A universal testing machine was used to apply a compressive load at a crosshead speed of 1 mm/min to the long axis of the tooth with a stainless-steel sphere until fracture occurred. One-way ANOVA followed by post hoc tests were used to assess the impact of preparation design on the fracture load of CAD-CAM lithium disilicate restorations.

RESULTS

The highest fracture load was recorded for CAD-CAM lithium disilicate indirect restorations for non-A-OVs preparation with margin (2549 ± 428 N) and onlay (2549 ± 293 N) and the lowest fracture load was recorded for CCCs (2389 ± 428 N); however, there was no significant (p = 0.640) between groups.

CONCLUSIONS

CAD-CAM lithium disilicate restorations fabricated for anatomical and non-A-OV preparation display a fracture resistance similar to CCCs. Conservative partial coverage restorations may be considered an acceptable approach for posterior teeth.

Influence of ceramic thickness and dental substrate on the survival rate and failure load of non-retentive occlusal veneers after fatigue

OBJECTIVE

To investigate the effect of ceramic thickness and dental substrate (enamel vs. dentin/enamel) on the survival rate and failure load of non-retentive occlusal veneers.

MATERIALS AND METHODS

Human maxillary molars (n = 60) were divided into five test-groups (n = 12). The groups (named DE-1.5, DE-1.0, DE-0.5, E-1.0, E-0.5) differed in their dental substrate (E = enamel, DE = dentin/enamel) and restoration thickness (standard: 1.5 mm, thin: 1.0 mm, ultrathin: 0.5 mm). All teeth were prepared for non-retentive monolithic lithium-disilicate occlusal veneers (IPS e.max Press, Ivoclar). Restorations were adhesively cemented (Syntac Classic/Variolink II, Ivoclar) and exposed to thermomechanical fatigue (1.2 million cycles, 1.6 Hz, 49 N/ 5-55°C). Single load to failure was performed using a universal testing-machine. A linear-regression model was applied, pairwise comparisons used the Student-Newman-Keuls method (p < 0.05).

RESULTS

Three dentin-based occlusal veneers (one DE-1.0, two DE-0.5) revealed cracks after fatigue exposure, which corresponds to an overall-survival rate of 95%. Load to failure resulted in the following ranking: 2142 N(DE-0.5) > 2105 N(E-1.0) > 2075 N(E-0.5) > 1440 N(DE-1.5) > 1430 N(DE-1.0). Thin (E-1.0) and ultrathin enamel-based occlusal veneers (E-0.5) revealed high failure loads and surpassed the standard thickness dentin-based veneers (DE-1.5) significantly (p = 0.044, p = 0.022).

CONCLUSION

All tested monolithic lithium disilicate occlusal veneers obtained failure loads above physiological chewing forces. Thin and ultrathin enamel-based occlusal veneers outperformed the standard thick dentin-based occlusal veneers.

CLINICAL SIGNIFICANCE

Minimally invasive enamel-based occlusal veneer restorations with non-retentive preparation design may serve as a conservative treatment option.

Minimally invasive CAD/CAM lithium disilicate partial-coverage restorations show superior in-vitro fatigue performance than single crowns

OBJECTIVE

To analyze the influence of restoration design (partial-coverage restoration vs. crown) and ceramic layer thickness on the performance and failure loads of CAD/CAM-fabricated lithium disilicate (LDS) reconstructions on molars after fatigue.

MATERIALS AND METHODS

Seventy-two posterior monolithic CAD/CAM-fabricated LDS restorations (IPS e.max CAD, Ivoclar Vivadent) with different occlusal/buccal ceramic layer thicknesses (1.5/0.8, 1.0/0.6, and 0.5/0.4 mm) and restoration designs (PCR: non-retentive full-veneer/partial-coverage restoration, C: crown,) were investigated and divided into six groups (n = 12, test: PCR-1.5, PCR-1.0, PCR-0.5; control: C-1.5, C-1.0, C-0.5). LDS restorations were adhesively bonded (Variolink Esthetic DC, Ivoclar Vivadent) to dentin-analogue composite dies (Z100, 3M ESPE). All specimens were subjected to thermomechanical loading (1.2 million cycles, 49 N, 1.6 Hz, 5-55°C) and exposed to single load to failure testing. Failure analysis was performed with light and scanning electron microscopies. Data were statistically analyzed using ANOVA, Tukey-Test, and t-test (p < 0.05).

RESULTS

Eight crown samples (C-0.5) and one PCR specimen (PCR-0.5) revealed cracks after fatigue, resulting in an overall success rate of 87.5% (crowns: 75%, PCRs: 96.88%). Direct comparisons of PCRs versus crowns for thicknesses of 0.5 mm (p < 0.001) and 1.0 mm (p = 0.004) were significant and in favor of PCRs. Minimally invasive PCRs (0.5 and 1.0 mm) outperformed crowns with the identical ceramic thickness. No difference was detected (p = 0.276) between thickness 1.5 mm PCRs and crowns.

CONCLUSIONS

Minimally invasive monolithic CAD/CAM-fabricated posterior LDS PCRs (0.5 and 1.0 mm) resulted in superior failure load values compared to minimally invasive crowns. Minimally invasive crowns (0.5 mm) are prone to cracks after fatigue.

CLINICAL SIGNIFICANCE

Minimally invasive CAD/CAM-fabricated LDS PCR restorations with a non-retentive preparation design should be considered over single crowns for molar rehabilitation.

Effect of hot-etching treatment duration on the shear bond strength of zirconia-to-resin cement

The surface of zirconia was treated with hot-acid etching of different durations to improve its shear bond strength to resin. Zirconia discs were subjected to untreated, sand-blasting, and hot-etching treatments for 10, 30 and 60 min. The discs were bonded to the surface of bovine enamel specimens using RelyX Ultimate resin cement. The bonded specimens were divided into immediate and thermocyling aging groups according to whether they underwent thermal cycling. A universal mechanical testing machine was used to measure the shear bond strength of the specimens. One-way analysis of variance was used to determine the effect of hot-etching time on the shear bond strength. In the immediate and thermocyling aging groups, 60 min of hot-etching provided significantly higher shear bond strength than the other conditions (p<0.05).

Survival and debonding resistance of posterior cantilever resin-bonded fixed dental prostheses for moderately and severely worn dentition during thermomechanical loading

OBJECTIVES

The purpose of this study was to investigate the survival rate, the debonding resistance, and the failure modes of different occlusal veneer designs when used as a retainer for posterior cantilever, resin-bonded fixed dental prostheses (RBFDPs) at two tooth wear levels.

METHODS

Four test groups were assigned: two groups with occlusal-proximal preparation (PT1 and PT2 for grade 2 and 3 wear), and two groups for occlusal-proximal and lingual preparation (PLT1 and PLT2 for grade 2 and 3 wear) Monolithic zirconia ceramic (3Y-TZP) RBFDPs were luted with an adhesive bonding system (Panavia V5). The specimens underwent a chewing simulation for 1.200.000 cycles with a load of 5 kg and thermocycling for 7500 cycles between 5 °C and 55 °C. The surviving restorations were debonded under quasi-static conditions. The results were analyzed with ANOVA.

RESULTS

The specimens exhibited a 100 % survival rate after thermomechanical fatigue loading. The debonding resistance was statistically significant higher for group PLT1 than for group PT1 (P = 0.004), and higher for group PT2 than group PT1 (P ≤ 0.001). However, the debonding resistance showed no statistically significant difference between groups PT2 and PLT2 (P = 0.343), and groups PLT1 and PLT2 (P = 0.222). Groups PT1 and PT2 showed favorable failure modes in 62.5 % and 0.00 % of the specimens, respectively. While groups PLT1 and PLT2 presented 25 % favorable failure modes.

SIGNIFICANCE

Occlusal veneers showed promising results as a retainer for cantilever RBFDPs. The lingual extension might increase debonding resistance. Nevertheless, conservative designs with lingual and proximal bevels are to be recommended, irrespective of the level of tooth wear.

Interaction of different concentrations of 10-MDP and GPDM on the zirconia bonding

OBJECTIVES

To analyze the influence of different concentrations of 10-MDP and GPDM used, combined or not, on the bonding to zirconia.

METHODS

Specimens of zirconia and a resin-composite (7 mm length, 1 mm width, and 1 mm thick) were obtained. The experimental groups were obtained according to the functional monomer (10-MDP and GPDM) and the concentrations (3 %, 5 %, and 8 %). For the groups with combined 10-MDP and GPDM, the agents were used with a proportion of 50 %/50 % wt until reaching the 3 %, 5 % and 8 % concentrations. All monomers were diluted in ethanol to obtain the primers. Two control groups were established: ethanol (negative control) and a commercial reference Monobond N (positive control). The zirconia surface treatment was performed with the primer application followed by the bonding to a resin-composite sample with a light-curing resin cement. Twenty-four hours after the adhesive procedure, a microtensile test was performed and the failure pattern of each sample was analysed with a stereoscopic magnifying glass. Data were analysed by a two-way ANOVA and Dunnet test.

RESULTS

All experimental primers presented a higher bond strength than the negative control (ethanol). Excepting the 8 % GPDM primer, all groups presented statistically similar bond strength compared to the positive control, with a predominance of adhesive failure.

SIGNIFICANCE

10-MDP, GPDM, and the combination of both for the concentrations tested promote an effective chemical bonding to zirconia. However, using 10-MDP and GPDM in the same primer has no synergistic effect.

Research Progress and Clinical Application of All-Ceramic Micro-Veneer

Anterior teeth problems affect the patient's daily eating, communication, social activities, self-confidence, and mental health. The trend in dentistry is to address anterior tooth problems with minimally invasive and aesthetic treatments. With the development of adhesive materials and ceramics, micro-veneers have been proposed as an alternative treatment for enhancing the aesthetic appearance and avoiding unnecessary tooth reduction. A micro-veneer is a veneer that can be cemented to the surface without or with minimal tooth preparation. These benefits include no need for anesthesia, postoperative insensitivity, good adhesion to enamel, reversibility of treatment, and higher patient acceptance. However, the micro-veneer repair is suitable only for specific cases and must be strictly controlled regarding indication. Treatment planning is a crucial step to achieving functional and aesthetic rehabilitation, and following the clinical protocol is helpful for the longevity and success of micro-veneer restorations. However, more precise and predictable tooth preparation methods, such as minimally invasive microscopic tooth preparation and digitally guided veneer preparation, are recommended rather than the traditional free-hand method. Therefore, this paper clarifies micro-veneers and compares them with other restorations to gain a deeper and more comprehensive understanding. The authors also review indications, materials, cementation, and effect evaluation of micro-veneers to provide clinicians with valuable information. In conclusion, micro-veneers are minimally invasive treatments that provide good restoration results when used appropriately and are worthy of promotion for the aesthetic restoration of anterior teeth.

Clinical outcomes and influence of material parameters on the behavior and survival rate of thin and ultrathin occlusal veneers: A systematic review

PURPOSE

Various oral rehabilitation approaches are available for severely worn dentition. However, evidence-based guidelines for permanent treatment are limited. This review aims to investigate clinical observational findings and compare in-vitro outcomes of thin and ultrathin occlusal veneers using different materials and approaches.

METHODS

An electronic search of online databases, such as PubMed (MEDLINE), BioMed Central (BMC), Cochrane, and Scopus, was performed for the 2009 - Jun 2021 period, following the PRISMA 2020 criteria. The reports sought for retrieval were all the articles evaluating the clinical outcomes of permanent full-mouth rehabilitation, and all in-vitro records that investigated and compared fracture strength, survival rate, and modes of failure of ultrathin (0.3 - 0.6 mm), thin (0.5 - 0.8 mm), and thick (0.8-1.5 mm) occlusal veneer restorations, with regard to the available indirect restorative materials. The Newcastle Ottawa risk of bias criteria was used to judge the clinical studies and a modified consort statement was used for the evaluation of in-vitro studies. The data of the included studies were extracted and grouped based on the similarity of the outcomes and study protocols. Data heterogeneity determined the qualitative and quantitative grouping of the results.

RESULTS

Two clinical and 17 in-vitro studies were included. Data exhibited heterogeneity within the materials, variables, testing protocols and observation periods. Therefore, only qualitative synthesis of the results was feasible. Clinically used 1 mm lithium disilicate overlays and ultrathin one-step no-prep polymer infiltrated ceramic network (PICN) occlusal veneers exhibited very high success and survival rates. The analysis of in-vitro studies exhibited variable survival rates and fracture load values, based on materials, thickness, and restorative approaches used.

CONCLUSIONS

Within the limitations of this systematic review, it can be concluded that the clinical outcomes of thin and ultrathin occlusal veneers/overlays are auspicious. In-vitro experimental results support the usage of the thin and ultrathin occlusal veneers.

Effect of phosphoric acid and sodium hydroxide on cleaning and bonding of saliva-contaminated feldspar porcelain

Purpose Hydrofluoric acid has been used to remove salivary contamination in dental glass-ceramics before bonding treatment. However, alternative methods are required because hydrofluoric acid is harmful. This study examined the cleaning effects of phosphoric acid and sodium hydroxide on glass-ceramics for bonding pre-treatment.Methods Feldspar porcelain was divided into four groups: (C) cleaned porcelain without any contamination, (S) porcelain contaminated with saliva, (SPA) porcelain cleaned with 37% phosphoric acid after saliva contamination, and (SSH) porcelain cleaned with 10% sodium hydroxide after saliva contamination. Each sample was bonded to the resin cement using a silane-containing primer. They were then subjected to a shear bond strength (SBS) test. Each surface was analyzed by scanning electron microscopy (SEM), contact angle measurements, and Fourier transform infrared spectroscopy (FT-IR).Results The SBS of group SSH was comparable to that of group C but significantly higher than that of groups S and SPA. SEM observations showed that saliva-like structures remained on the samples of groups S and SPA, but not on the SSH group. The contact angles of groups C and SSH were comparable and significantly smaller than those of groups S and SPA, respectively. FT-IR analysis also revealed saliva in groups S and SPA, which was absent in the SSH group.Conclusions The saliva remained on the porcelain even after cleaning with phosphoric acid, and SBS was not restored to the same level as before the contamination. In contrast, sodium hydroxide eliminated saliva and restored SBS to the same level as before contamination.

Color stability and surface roughness of ormocer- versus methacrylate-based single shade composite in anterior restoration

Background

The blending ability of universal shade composites and their stability in the oral environment are of great concern in restoring anterior teeth. This study aims to evaluate and compare the color stability and surface roughness of two single-shade composite restorations, ormocer-based composite (OBC) and methacrylate resin-based composite (RBC), after storing them in different staining media.

Materials and methods

In this study, two universal shade composite restorative materials were tested: a nanohybrid OBC (Admira fusion X-tra, Voco) and a supra-nanofilled RBC (Omnichroma, Toukyama). In total, 60 cylindrical centralized cavities (diameter: 5 mm, depth: 2 mm) were prepared in sound extracted-human central incisors and divided into two equal groups according to the restorative material used (n = 30). According to the storage media, the teeth of each group were divided into three subgroups (n = 10): artificial saliva, black tea, and cola. The restoration color was evaluated for all teeth at baseline and after four weeks of storage. The color stability (∆E) was measured using a reflective spectrophotometer (X-Rite, model RM200QC, Neu-Isenburg, Germany). The surface roughness (Ra) was evaluated using three-dimensional optical profilometry (Wyko, Model NT 1100, Veeco, Tucson, USA). Additionally, the extracted data were analyzed using two-way analysis of variance (ANOVA), one-way ANOVA and Student’s t-test.

Results

In the baseline evaluation, there were no statistically significant differences with respect to color matching or surface roughness results between the two studied restorative materials. However, the differences were statistically significant after storing them in different media.

Conclusion

Universal composites showed satisfactory color matching with different teeth colors and accepted surface smoothness, whereas the aging procedure exerted a negative effect on their color stability and surface characteristics.

Effect of preparation design on marginal adaptation and fracture strength of ceramic occlusal veneers: A systematic review

OBJECTIVES

This systematic review aims to investigate the effect of different preparation designs on the marginal fit and fracture strength of ceramic occlusal veneers.

MATERIALS AND METHODS

Based on the PICO question and the search terms, an electronic search was performed in Google Scholar, PubMed (MEDLINE), Scopus, Cochrane Library, Web of Science, Science Direct, Wiley, Ovid, and SAGE for articles published up to July 2022. After including English in vitro studies that evaluated posterior ceramic occlusal overlays at the posterior with ceramic restorations by following the PRISMA statement, the extracted data was tabulated. The methodological quality of the included studies was evaluated. Risk of bias assessment was done independently by two authors using the modified MINORS scale.

RESULTS

About 3138 search results were screened, of which 22 were selected due to their titles. Twenty-one full-text articles were assessed for eligibility. Seventeen in-vitro studies were finalized for the extraction of quantitative data. All 17 articles had a low risk of bias and were retained. The influencing items for evaluating the research were different in most studies; therefore, qualitative synthesis of the results was feasible. They generally included preparation design, material thickness, depth of preparation in the tooth, internal divergence angle, and finish line. Meta-analysis was not done due to heterogeneity of preparation types and evaluation methods. Results revealed that fracture resistance of occlusal veneers is higher than normal mastication force, and it is sufficient to prepare the occlusal surface, use a self-etching primer for bonding, and an acceptable minimum ceramic thickness. The marginal discrepancy of occlusal veneers is clinically acceptable. However, this systematic review faces some limitations due to the lack of in vivo studies, different preparation designs in included studies, different follow-ups, and lack of comprehensive explanations in articles.

CONCLUSIONS

The preparation design of occlusal veneers influences both marginal adaptation and fracture resistance. Various preparation designs are proven to have clinically acceptable fracture strength and marginal adaptation.

Ultrathin CAD-CAM glass ceramic and composite resin occlusal veneers for the treatment of severe dental erosion: An up to 3-year randomized clinical trial

STATEMENT OF PROBLEM

Ultrathin bonded posterior occlusal veneers represent a conservative alternative to traditional onlays and complete coverage crowns for the treatment of erosive dental wear. Data regarding the clinical performance of ceramic and composite resin ultrathin occlusal veneers are lacking.

PURPOSE

The purpose of this prospective randomized clinical trial was to evaluate the influence of computer-aided design and computer-aided manufacturing (CAD-CAM) restorative material (ceramic versus composite resin) on the clinical performance of ultrathin occlusal veneers bonded to worn posterior teeth.

MATERIAL AND METHODS

Eleven participants (mean age, 30.4 years) had their posterior teeth restored with 24 ceramic (e.max CAD) and 36 composite resin (Lava Ultimate) ultrathin occlusal veneers. The material type was assigned randomly. The tooth preparations were trial restoration driven and included immediate dentin sealing (OptiBond FL). The intaglio surfaces of the ceramic restorations were etched with hydrofluoric acid and silanated, and the composite resins were airborne-particle abraded and silanated. The tooth preparations were airborne-particle abraded and etched with phosphoric acid before restoration insertion. All restorations were adhesively luted with preheated composite resin (Filtek Z100). The participants were evaluated according to the modified United States Public Health Service (USPHS) criteria at baseline and then each year for up to 3 years. Survival rates were estimated with time to failure (primary outcome of interest) as the endpoint (scores 4 or 5).

RESULTS

No restorations were lost. Five partial failures, in the form of chipping (all scored 4), were observed in the composite resin group (Lava Ultimate). The Kaplan-Meier survival rates were 100% for ceramic and 84.7% (SE 0.065%) for composite resin. Differences between the 2 groups were not statistically significant (P=.124). In the surviving restorations, significant difference (P=.003) was found for surface roughness as restorations in the composite resin group experienced some surface degradation.

CONCLUSIONS

The findings of this medium-term clinical trial suggest that ceramic (e.max CAD) and composite resin (Lava Ultimate) CAD-CAM ultrathin occlusal veneers presented statistically comparable performance regardless of the minor partial failures (restorable chipping) observed in the composite resin group. Higher surface degradation was observed in the composite resin group.

Increasing Acid Concentration, Time and Using a Two-Part Silane Potentiates Bond Strength of Lithium Disilicate-Reinforced Glass Ceramic to Resin Composite: An Exploratory Laboratory Study

There is still a lack of consensus concerning the recommended etching concentration, application time and type of silane when bonding lithium disilicate-reinforced glass ceramics manufactured by CAD/CAM. The purpose of this study was thus to conduct an in vitro study which investigates the influence of hydrofluoric acid (HF) concentration, etching time and silane type on the microtensile bond strength (μTBS) of lithium disilicate to resin composites. Thirty-nine IPS e.max CAD blocks were randomly divided between thirteen groups (n = 3). The variables were HF concentration (9.5 or 4.9%), etching time (20 or 60 s) and silane type (Bis-Silane, Monobond Plus and ESPE Sil Silane). The blocks were cut into beams, aged for 10,000 cycles in a thermocycler and submitted to tensile stress to determine μTBS. A control group featuring the Monobond Etch & Prime (MEP) agent that combines etching/silanisation into a simultaneous process was also added. This group was discarded from the analysis due to only having pre-test failures. The data were analysed using a three-way ANOVA (α = 0.05). The HF concentration, etching time and silane type significantly influenced μTBS (p < 0.001). Significant interactions between time and silane type (p = 0.004), HF concentration and silane type (p < 0.001) and among the three factors (p < 0.001) were noted. Etching lithium disilicate with 9.5% HF (60 s), followed by the application of Bis-Silane, resulted in the highest μTBS (16.6 ± 9.0 MPa). The highest concentration and etching time under study, combined with a two-part silane, resulted in the highest bond strength, while the application of MEP showed a complete pre-test failure.

Posterior minimally invasive full-veneers: Effect of ceramic thicknesses, bonding substrate, and preparation designs on failure-load and -mode after fatigue

OBJECTIVE

To evaluate the effect of ceramic thicknesses, bonding surface (enamel vs. dentin), and preparation design (box vs. no box) on the fatigue survival and failure load of minimally invasive full-veneer restorations.

MATERIALS AND METHODS

Human-premolars (n = 60) were divided into five test groups (n = 12). All teeth received full-veneer preparation with the following occlusal/labial thicknesses: standard: 1.5/0.8 mm; thin: 1.0/0.6 mm; ultrathin 0.5/0.4 mm. Preparations for each ceramic thickness were refined in enamel (E-1.0 and E-0.5) or dentin (D-1.5, D-1.0, and D-0.5). Control groups DB-1.5, EB-1.0, and EB-0.5 received box preparations. Monolithic lithium disilicate restorations (IPS-e.max-Press, Ivoclar Vivadent) were adhesively cemented (Syntac-Classic/Variolink-II, Ivoclar Vivadent) and subjected to cyclic mechanical loading (F = 49 N, 1.2 million cycles) with simultaneous thermocycling (5-55°C). All specimens were exposed to single load-to-failure. Pair-wise differences were calculated by using a linear regression model and Student-Newman-Keuls method (p < 0.05).

RESULTS

All full-veneers of group D-1.5, E-1.0, E-0.5, DB-1.5, EB-1.0, and EB-0.5 survived fatigue. Two full-veneers (D-1.0 and D-0.5) revealed cracks during fatigue, resulting in an overall fatigue survival rate of 98.1%. Mean load-to-failure values (N) were as followed: 1005 (D-1.5); 866 (D-1.0); 816 (D-0.5); 1495 (E-1.0); 1279 (E-0.5); 1129 (DB-1.5); 1087 (EB-1.0); and 833 (EB-0.5). Irrespective of ceramic thicknesses, enamel-based full-veneers resulted in higher failure loads than dentin-based restorations. Box preparation reduced the failure loads of thin and ultrathin enamel-based restorations.

CONCLUSION

All tested monolithic lithium disilicate full-veneer restorations exceeded physiological masticatory forces. Minimally invasive full-veneer restorations with enamel as a bonding surface and a non-retentive preparation design showed superior performance.

CLINICAL SIGNIFICANCE

Enamel-based non-retentive full-veneers made of monolithic lithium disilicate may serve as a reliable and esthetical minimally invasive treatment option for premolars.

Clinical and Biomechanical Performance of Occlusal Veneers: A Scoping Review

AIM

This manuscript aims to evaluate, through a scoping review, current knowledge of the biomechanical behavior, materials, preparations, and limitations of occlusal veneers.

BACKGROUND

Occlusal veneers are a minimally invasive alternative for the additive restoration of posterior teeth with significant loss of the occlusal structure. This type of restoration has been emerged in recent years as an alternative to invasive treatment, which in the same way seeks to restore the structure of the posterior teeth. All this is because in recent years restorative dentistry has focused a large part of its objectives on conservative therapies.

REVIEW RESULTS

Five electronic databases-PubMed, Cochrane, LILACS, EMBASE, and Google Scholar-were searched. Title and abstracts were independently screened by three reviewers, followed by a full-text review. A total of 42 articles met our inclusion criteria; most of these studies were in vitro (n = 35) and other studies were clinical studies (n = 7). These in vitro studies included 21 studies that analyzed the type of preparation and 6 studies that evaluated the limitations of occlusal veneers.

CONCLUSION

Thicknesses between 0.7 and 1.0 mm are recommended for ceramic materials; in addition, thicknesses less than 0.7 mm are recommended to use polymeric materials. The materials used for this type of restoration are plastic- and ceramic-based materials, whose load resistance values were found to exceed 2000 N in most studies. It is recommended to carry out a minimally invasive preparation or not to carry out a dental preparation, as long as there is a peripheral enamel to make an external bevel that redirects the eccentric forces to the axis of the tooth.

CLINICAL SIGNIFICANCE

Restorative dentistry has moved toward conservative treatments with the least amount of dental tissue being removed. Occlusal veneers appear to be a conservative option in the reconstruction of tooth tissues lost due to tooth wear and in cases where it is necessary to restore or increase the vertical dimension.

Fracture Resistance and Failure Mode of Mandibular Molar Restored by Occlusal Veneer: Effect of Material Type and Dental Bonding Surface

This study assesses the effect of the material type (lithium disilicate, zirconia, and polymer-infiltrated ceramic) and dental bonding substrates (dentin, dentin with intra-coronal cavity, and dentin with composite filling) on the fracture resistance and failure mode of molars restored by occlusal veneers. Methods: Ninety occlusal veneers, fabricated from either lithium disilicate, zirconia, or polymer-infiltrated ceramic, were adhesively bonded to teeth prepared with either dentin, dentin with intra-coronal cavity, or dentin with composite filling. All specimens were thermally aged (5000 cycles), then load cycled (120,000 cycles). Each specimen was subjected to a compressive load through fracture, then was examined (×20) to identify the fracture type. Data were statistically analyzed. Results: Material type and dental substrate had no significant effect on the fracture resistance of adhesively retained occlusal veneer restorations. For each material, no significant differences were found between veneers bonded to dentin, dentin with intra-coronal cavity, and dentin with composite filling. Additionally, within each bonding substrate, there were no significant differences between lithium disilicate, zirconia, and polymer-infiltrated ceramic veneers. The adhesive failure was recorded mainly with zirconia occlusal veneer restorations. Conclusions: Considering the fracture results, lithium disilicate, zirconia, and polymer-infiltrated ceramic occlusal veneers perform well whatever the type of dental bonding surface. When the dental bonding surface varies, different occlusal veneer materials should be considered. Occlusal veneers bonded to dentin, dentin with composite filling, or dentin with an intra-coronal cavity exhibited a fracture resistance exceeding the average human masticatory forces in the molar area.

Comparison of Fracture Resistance for Chairside CAD/CAM Lithium Disilicate Crowns and Overlays with Different Designs

PURPOSE

To determine the fracture resistance of chairside computer-aided design and computer-assisted manufacturing (CAD/CAM) lithium disilicate full coverage crowns and two different designs of overlay restorations for premolars.

MATERIALS AND METHODS

CAD/CAM lithium disilicate (IPS e.max CAD for CEREC/HT A1 C14, Ivoclar Vivadent) restorations (15 specimens/group) with 1.5 mm occlusal thickness and 1.0 mm chamfer were designed and fabricated with a chairside CAD/CAM system (CEREC, Dentsply Sirona). The restorations were prepared in three different designs: (1) full coverage crowns, (2) overlays with the margin located 2 mm above the gingiva, and (3) overlays with the margin located 4 mm above the gingiva. Restorations were cemented using conventional resin luting cement (Multilink, Ivoclar Vivadent) with primer system (Monobond Plus, Ivoclar Vivadent) to resin printed dies, load cycled (2,000,000 load cycles at 1 Hz with 275 N force), and then finally loaded with a steel indenter until failure. Scanning electron microscopy observations of fractured surfaces were also conducted. Group results were analyzed with one-way analysis of variance, and the medians were evaluated independently with Kruskal-Wallis.

RESULTS

The fracture force of CAD/CAM lithium disilicate restorations was significantly different (p < 0.001) depending on the design of the restoration. Full coverage crowns showed significantly higher force to fracture (1018.8 N) than both types of overlays (p = 0.002 for overlay 2.0 mm and p < 0.001 for overlay 4.0 mm above gingiva). Among the two overlays, the restoration with the margin located 2 mm above the gingiva showed significantly higher fracture force (813.8 N) than the overlay with margin at 4 mm above the gingiva (436.1 N; p < 0.001). The fracture appearance of the crowns was much more complex than that of the overlay restorations.

CONCLUSIONS

Full coverage chairside CAD/CAM lithium disilicate premolar crown showed higher fracture resistance than overlay restorations. Overlays with the margin located 2 mm above the margin demonstrated higher resistance than those with the margin located 4 mm above the gingiva.

Fatigue failure and success rate of lithium disilicate table-tops as a function of cement thickness

PURPOSE

Under thin, partial coverage restoration the proper cement thickness to be clinically employed still remains an issue. The aim of this study was to determine the failure and success rates of simplified lithium disilicate occlusal veneers as a function of cement thickness. The null hypothesis was that cement thickness has no effect on the fatigue resistance.

METHODS

Sound human molars were severed in a plane parallel to the occlusal surface to create a flat dentin surface surrounded by enamel edges. Forty-five occlusal veneers 1.0 mm thick (IPS e.max CAD LT) were luted to the teeth with Multilink Automix resin cement, creating 3 experimental groups (n=15) with cement thicknesses of 50, 100, and 200 µm. The restorations were fatigue-cycled using a ball mill machine containing zirconia and stainless steel spheres. Twelve 60 min cycles were performed. Survival statistics were applied to "failure" and "success" events, comparing the three groups using a log-rank Mantel-Cox test and a log-rank test for trends (alpha = 0.05).

RESULTS

The failure and success rates were not significantly influenced by cement thickness (P = 0.137 and P = 0.872, respectively); thus, the null hypothesis was accepted. However, when log-rank test for trends was applied to failure events, the tendency to have less failures with increasing thicknesses was found statistically significant (P = 0.047).

CONCLUSIONS

The cement thickness within the range adopted here did not have a significant effect on the failure or success rate of lithium disilicate occlusal veneers when exposed to randomized impact stresses generating fatigue phenomena.

Effect of various digital cement space settings on the adaptation of CAD/CAM occlusal veneer "micro-ct evaluation"

The aim was to evaluate the adaptation of CAD/CAM occlusal veneer with different cement space settings using micro CT scan. Three groups of IPS e.max-CAD lithium disilicate occlusal veneers with different cement space settings (30, 40, and 50 µm) were produced. A circle with 20 different diameters was centered at the center of the same image position of every scanned specimen using micro CT scan to measure four different locations [Occlusal (OCG), axial (AXG), Marginal (MAG), and absolute marginal discrepancy values (AMD)]. Kruskal-Wallis test revealed that there were no statistical differences between (OCG), (AXG), and (AMD) tested groups (p>0.05), and statistical differences between (MAG) group and other two groups (p<0.05). An increase in the digital cement space significantly improved the marginal fit of IPS e.max-CAD occlusal veneer.

Fracture load of CAD/CAM ultrathin occlusal veneers luted to enamel or dentin

OBJECTIVES

To evaluate, in vitro, the fracture load of IPS e.max CAD occlusal veneers at thicknesses of either 0.3 or 0.6 mm luted to enamel or dentin.

MATERIALS AND METHODS

Fifty human molars were randomly distributed into five groups (n = 10): G1 - healthy teeth (control); G2-0.3-mm-thick veneers luted to enamel; G3-0.6-mm-thick veneers luted to enamel; G4-0.3-mm-thick veneers luted to dentin; and G5-0.6-mm-thick veneers luted to dentin. After the luting procedures, the specimens were immersed in distilled water at 37°C for 24 hours and then subjected to mechanical loading (10⁶  cycles at 200 N load). The specimens were subjected to a fracture load test in a universal testing machine. Two-way ANOVA and Tukey's test (α = 0.05) were used to analyze data.

RESULTS

Only the thickness factor was significant (P = .002). Values of fracture load followed by distinct letters represent significant differences (P < .05): G1 (3204 N ± 730)^ab ; G2 (3144 N ± 729)^ab ; G3 (2489 N ± 606)^b ; G4 (3591 N ± 776)^a ; and G5 (2770 N ± 598)^ab .

CONCLUSION

IPS e.max ultrathin occlusal veneers luted to enamel or dentin obtained fracture load comparable to that of the healthy tooth.

CLINICAL SIGNIFICANCE

IPS e.max CAD ultrathin occlusal veneers at 0.3 or 0.6-mm-thick seem to provide good perspectives in relation to the clinical use.

Annual review of selected scientific literature: A report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

This comprehensive review of the 2019 restorative dental literature is offered to inform busy dentists regarding remarkable publications and noteworthy progress made in the profession. Developed by the Scientific Investigation Committee of the American Academy of Restorative Dentistry, each author brings discipline-specific expertise to 1 of 8 sections of the report: (1) prosthodontics; (2) periodontics, alveolar bone, and peri-implant tissues; (3) implant dentistry; (4) dental materials and therapeutics; (5) occlusion and temporomandibular disorders; (6) sleep-related breathing disorders; (7) oral medicine and oral and maxillofacial surgery; and (8) dental caries and cariology. The report targets important information likely to influence day-to-day dental treatment decisions. Each review is not intended to stand alone but to update interested readers so that they may visit source material when greater detail is desired. As the profession moves toward evidence-based clinical decision-making, an incredible volume of potentially valuable dental literature continues to increase. It is the intention of this review and its authors to provide assistance in negotiating the extensive dental literature published in 2019. It is our hope that readers find this work useful in the clinical management of dental patients.