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.

[Four-year follow-up study of onlay and occlusal veneer restorations on posterior teeth].

OBJECTIVE: To investigate the survival rate and clinical failure reasons of onlay and occlusal veneer restorations retrospectively, and to put forward valuable suggestions for the selection of clinical indications. METHODS: A total of 102 patients and 124 teeth treated by one of the authors from 2016 to 2019 were subjected to CAD/CAM lithium silicate reinforced glass-ceramic onlay or veneer restorations of premolars and molars, including 43 teeth with pulp vitality, 81 endodontic treated teeth, and occlusal thickness of restoration was 1.5 mm. After four years of restoration, retrospective surveys were conducted to record the survival rate of restorations, the causes of restoration failure, and patient satisfaction rates, and the survival rate of restorations between vital teeth and endodontic treated teeth and among restored teeth was statistically analyzed by Chi-square test. RESULTS: The survival rates of restorations on vital teeth and endodontic treated teeth were 95.5% and 90.0%, respectively, the average survival rate was 90.2%. The survival rates of vital teeth were higher than those of endodontic treated teeth without statistical difference. There was also no statistically significant difference among the tooth locations. The causes of failure included the cracking of the restoration, the loss of the restoration, the fracture of the abutment teeth, secondary caries below the adjacent contact point, and food impaction caused by the loosening of the adjacent contact point. The overall patient satisfaction rate was 91.5%. CONCLUSION: The 4-year survival rate of glass-ceramic onlays and occlusal veneers is lower than that of the full crown restoration, and there are more complications than that of the single-crown restorations. The design of the restoration should be carefully selected based on the vitality of the abutment tooth and the remaining amount of tooth tissue. When there is too little tooth structure left, a post and crown should be selected for restoration. Adequate strength and thickness of the restoration should be ensured to prevent food impaction. Due to the small amount of abutment tooth preparation, it has the advantages of less stimulation of the pulp and periodontal tissue, and can be recommended as a trial restoration.

Fatigue behavior, failure mode, and stress distribution of occlusal veneers: influence of the prosthetic preparation cusp inclinations and the type of restorative material.

OBJECTIVE: To evaluate the effects of cusp inclination of the prosthetic preparation's occlusal surface and type of restorative material on the fatigue behavior, failure mode, and stress distribution of occlusal veneers. MATERIALS AND METHODS: Glass fiber-reinforced epoxy resin prosthetic preparations for occlusal veneers with three different occlusal surface cusp inclination degrees (0°, 15°, and 30°) were produced and assigned into six testing groups (n = 11) according to the cusp inclination (0°, 15°, or 30°) and type of restorative material (lithium disilicate-LD or resin composite-RC). Despite different substrate preparation cusp inclination degrees, the restorations were designed maintaining 30° inclination between the cusps at the occlusal surface and a thickness of 0.7 mm at the central groove region of the restorations to be machined in a CAD/CAM system. After cementation, the specimens were stored for about 7 days (under water at 37 °C), and subsequently submitted to a load to failure test (n = 2) and an intermittent cyclic fatigue test (n = 9) (initial load: 100 N; step size: 50 N; cycles/step: 10,000; loading frequency: 20 Hz; loading piston: 6-mm-diameter stainless steel) until observing cracks. The data were analyzed by two-way ANOVA, Kaplan-Meier, and Mantel-Cox post hoc tests. Finite element analysis (FEA) and fractographic analyses were performed. RESULTS: The fatigue performance of LD and RC occlusal veneers was evaluated based on different prosthetic preparation cusp inclinations. The 0° inclination showed the best fatigue performance for both materials (LD: 944N, RC: 861N), while the 15° and 30° inclinations had lower values (LD: 800N and 533N, RC: 739N and 717N, respectively). The study also found that for a 0° inclination, LD occlusal veneers performed better than RC ones (LD: 944 N > RC: 861N), while for a 30° inclination, RC occlusal veneers had better fatigue performance than LD ones (LD: 533N < RC: 717N). No significant difference was observed between the materials for a 15° inclination (LD: 800N = RC: 739N). The FEA results showed a higher tensile stress concentration on lithium disilicate than on resin composite occlusal veneers. All lithium disilicate occlusal veneers showed radial crack failures, while resin composite occlusal veneers showed Hertzian cone cracks and radial cracks combined. CONCLUSION: Considering mechanical perspective only, RC occlusal veneers should be indicated when prosthetic preparation cusps inclinations are 30°. When 0° prosthetic preparation cusps inclinations are observed, LD occlusal veneers will behave mechanically better. When a 15° cusp inclination is preserved, both restorative materials behave similarly.

Influence of thickness and surface conditioning on fracture resistance of occlusal veneer.

BACKGROUND: The purpose of the current study was to assess the impact of restoration thickness, surface conditioning and the interaction between them on the fracture resistance of CAD/CAM fabricated lithium disilicate occlusal veneers. METHODS: A total of 42 maxillary molars were prepared to receive CAD/CAM fabricated lithium disilicate occlusal veneer either with 0.5 mm (n = 21) or 1 mm (n = 21) thickness. Each main group was divided into 3 subgroups (n = 7), according to surface treatment, HF acid (HF-1, HF-0.5), acidulated phosphate fluoride (APF-1, APF-0.5) and Monobond etch & prime (MON-1, MON-0.5). Multilinik N (Ivoclar-Vivadent) adhesive resin cement was used for bonding according to the manufacturer instructions. One hour after bonding, specimens were stored in water bath for 75 days followed by cyclic loading fatigue for 240,000 cycles to simulate clinical situation. Finally, specimens were fractured under compressive load in (N) using a universal testing machine. Two and one-way ANOVA and Post Hoc Tukey test were used for statistical analysis. RESULTS: The means ± SD (N) fracture load for each group were calculated. MON-1 group showed the highest fracture load (1644.7 ± 155.3) followed by HF-1 group (1514.6 ± 212.5). Meanwhile, APF-0.5 showed the lowest fracture load (962 ± 249.6). CONCLUSION: CAD/CAM fabricated lithium disilicate occlusal veneers can be used with a thickness of 0.5 mm instead of conventional crowns. Monobond etch & prime is recommended as a surface treatment for CAD/CAM fabricated lithium disilicate occlusal veneer due to biological hazards of Hydrofluoric acid.

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.

[Morphology accuracy evaluation of direct composite occlusal veneer using two types of modified stamp-technique].

OBJECTIVE: To evaluate the morphology accuracy of direct occlusal veneer using two types of modified stamp-technique, comparing the Results of two types of stamp and different composite resin. METHODS: Model scanner was used to get the original data from the standard resin teeth in plastic model. Two types of stamps were made: solid silicon stamp and transparent silicon stamp. In the study, 54 resin tooth were randomly divided into 9 groups: Groups 1-8 were restored by direct composite resin, using general and bulk-filled composite resin in occlusal veneer (1 mm or 2 mm) with two types of stamp-technique (the solid silicon, and the transparent silicon), and the control group was restored by indirect way using CAD/CAM composite resin restoration by biocopy technique to mimic the original shape of the teeth. After the resin teeth were prepared for occlusal veneer, the direct and indirect composite resins were restored. After the restoration was finished, the data were obtained again by the same model scanner in the plastic model. 3D comparisons were made using the original and restoration data, the average difference and the root mean square of difference (RMS) were recoded from the software. The RMS of all the groups were analyzed using one way ANOVA (α=0.05). RESULTS: The RMS of occlusal surface in solid silicon stamp group was (0.136±0.031) mm, in transparent silicon group was (0.130±0.024) mm, and in control group was (0.130±0.009) mm. There were no significant difference. While the RMS of buccal/lingual surface in solid silicon stamp group was the smallest [(0.135±0.020) mm, P < 0.05], and in transparent silicon group it was (0.147±0.021) mm, and control group (0.153±0.014) mm. The general composite resin using the two types of stamp had the largest occlusal RMS in 2 mm occlusal veneer, which were significantly larger than control group (P < 0.05). CONCLUSION: The direct occlusal veneer using two types of modified "stamp-technique" had relatively good morphology accuracy. Direct occlusal veneer using bulk-filled composite resin made with two types of stamp technique had even more accurate morphology than using general composite resin. The solid silicon stamp had a better morphology accuracy in buccal/lingual surface than the transparent silicon stamp.

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.

Estimation of stress distribution and risk of failure for maxillary premolar restored by occlusal veneer with different CAD/CAM materials and preparation designs.

OBJECTIVES: To compare stress distribution and failure probability in maxillary premolars restored by simple occlusal veneer (SOV) and buccal-occlusal veneer (BOV) with 3 different CAD/CAM materials. MATERIALS AND METHODS: A maxillary premolar was digitized by a micro-CT scanner. Three-dimensional dynamic scan data were transformed, and finite element models of 2 different models (SOV and BOV restored teeth) were designed. Three different CAD/CAM materials, including lithium disilicate glass ceramic (LD) IPS e.max CAD, polymer-infiltrated ceramic-network (PICN) Vita Enamic, and resin nano-ceramic (RNC) Lava Ultimate, were designated to both veneers. Maximum principle stresses were determined by applying a 300-N axial load to the occlusal surface. Weibull analyses were performed to calculate the failure probability of the models. RESULTS: LD-restored teeth showed the highest stress in the veneer, lowest stress in substrate teeth, and lowest failure probability for the overall system; RNC-restored teeth showed the lowest stress in the veneer, highest stress in substrate teeth, and highest failure probability. No significant differences were found in the cement layer among the different models. No significant differences of stress and failure probability existed between SOV and BOV preparations. CONCLUSIONS: CAD/CAM composite resin occlusal veneers bear lower maximum stress than ceramic veneers. Teeth restored by composite veneers are more prone to failure than those restored by ceramic veneers. Additional reduction of the buccal surface did not increase the stress on the occlusal veneer under axial load. CLINICAL RELEVANCE: Both occlusal veneers could be used under physiological masticatory force. CAD/CAM glass ceramic was safer than composite resins.

Comparison of Fracture Load and Surface Wear of Microhybrid Composite and Ceramic Occlusal Veneers.

PURPOSE: To compare in vitro fracture load, surface wear, and roughness after thermal cycling and cyclic mechanical fatigue loading among cemented microhybrid resin-based composite and ceramic occlusal veneers fabricated at two thicknesses (1.5 and 2.5 mm). MATERIALS AND METHODS: Sixty-four extracted premolars without root canal treatment were prepared and restored with occlusal veneers of two thicknesses (1.5 and 2.5 mm), using four different materials: microhybrid composite (MC), fiber-reinforced microhybrid composite (FMC), heat-pressed lithium disilicate ceramic (HPC), and computer-aided design/computer-aided manufactured lithium disilicate ceramic (CCC). The specimens underwent thermal cycling and cyclic mechanical fatigue loading, and were then subjected to fracture testing, with loads at failure recorded as fracture load. Wear and surface roughness were recorded before and after fatigue loading. Results were analyzed using one-way ANOVA, two-way ANOVA (α = 0.05). RESULTS: All specimens survived thermal cycling and cyclic mechanical fatigue loading. At 1.5-mm thickness, the mean fracture load of FMC was highest (3926.48 ± 556.54 N), while that of CCC was highest (3066.45 ± 559.94 N) at 2.5 mm. Regardless of thickness, the fracture load of CCC was higher than that of HPC (p = 0.004 and p = 0.023). The wear of MC and FMC was significantly higher than those of HPC and CCC (p ≤ 0.001), but was similar in terms of the wear rate of tooth enamel. HPC exhibited the lowest surface roughness after fatigue loading (p ≤ 0.001). CONCLUSION: All tested occlusal veneers exhibited a fracture load considerably exceeding the maximum occlusal force in the posterior dentition. When the attainable space for restoration varies, different occlusal veneer materials should be considered. The surface wear and roughness also need to be considered when selecting materials.

Prognostic factors associated with pulp status in patients with cracked teeth treated with occlusal veneer: A 6- through 24-month prospective clinical study.

BACKGROUND: The authors evaluated the prognostic factors associated with pulp status in patients with cracked teeth (CT) treated with occlusal veneer. METHODS: An analysis of 80 CT (71 patients) with 1 or more crack lines (CLs) and normal pulp vitality or reversible pulpitis was performed. All patients received occlusal veneer and their demographic and clinical data were recorded. Pulp status and clinical features were recorded at 1 week and posttreatment at 1, 2, 3, 6, 12, 18, and 24 months. RESULTS: Maxillary first molars were commonly involved (30 [38%]). The number of CLs on the finish line ranged from 1 through 7 and most had 3 CLs (24 [30%]). The number of CLs through preparation on the finish line ranged from 0 through 4, and 2 CLs (42 [53%]) were the most prevalent. During follow-up, 5 of 80 CT progressed to pulp disease, resulting in a success rate of 93.8%. Results of the Cox model and Kaplan-Meier analysis showed that probing depth greater than 6 mm, widening periodontal ligament of apical area, more than 4 CLs on finish line, and more than 2 CLs through preparation on the finish line were risk factors associated with pulp status (P < .05). CONCLUSIONS: Occlusal veneer can protect CT without preventive root canal therapy. PRACTICAL IMPLICATIONS: The success rate and risk factors of pulp disease in CT restored with occlusal veneer are reported.

3D-printed versus conventionally milled zirconia for dental clinical applications: Trueness, precision, accuracy, biological and esthetic aspects.

OBJECTIVES: This systematic review aimed to compare the clinical outcome, internal gap, trueness, precision, and biocompatibility of 3D-printed (AM) compared to milled (SM) zirconia restorations. DATA SOURCE: A thorough search of Internet databases was conducted up to September 2023. The search retrieved studies compared AM zirconia to SM zirconia restorations regarding clinical outcome, fit, trueness, precision, and biocompatibility. STUDY SELECTION: Of 1736 records, only 59 were screened for eligibility, and 22 records were included in this review. The quality of studies was assessed using the revised Cochrane risk-of-bias tool (ROB2), and the Modified Consort Statement. One clinical study exhibited a low risk of bias. All laboratory studies revealed some bias concerns. Short-term observation showed 100 % survival with no signs of periodontal complications. 3D-printed zirconia crowns showed statistically significant lower ΔE and a better match to adjacent teeth (p ≤ 0.5). The fit, trueness, and precision vary with the printing technique and the tooth surface. CONCLUSIONS: 3D-printed zirconia crowns provide better aesthetic color and contour match to adjacent natural teeth than milled crowns. Both 3D printing and milling result in crowns within the clinically acceptable internal and marginal fit. Except for nanoparticle jetting, the marginal gap of SM crowns was smaller than AM crowns, however, both were clinically acceptable. Laminate veneers might be more accurately produced by 3D printing. 3D-printed axial surface trueness was better than milled axial surfaces. Long-term RCTs are recommended to confirm the clinical applicability of 3D-printed restorations. CLINICAL SIGNIFICANCE: Internal fit and gap, precision, and trueness are fundamental requirements for successful dental restorations. Both techniques produce restorations with clinically acceptable marginal and internal fit. Axial surfaces and narrow or constricted areas favored 3D-printed than conventionally milled zirconia.

Fracture load of ultrathin occlusal veneers: Effect of thickness and surface conditioning.

OBJECTIVE: This in-vitro study is planned to analyze the effect of different thicknesses of ceramic occlusal veneers and different surface treatments on fracture resistance. MATERIALS AND METHODS: A total of 48 sound mandibular molars are anatomically prepared from the occlusal surface with two different thicknesses (1.0 and 0.5 mm). CAD/CAM zirconia-reinforced glass ceramic blocks (Vita Suprinity) are used for fabricating occlusal veneers. The teeth are randomly divided into two primary groups A and B (n=24) according to occlusal veneer thickness. Each group is subdivided according to surface conditioning into three equal subgroups (n=8)-subgroup HF: etching with hydrofluoric acid and ceramic primer application; subgroup APF: etching with acidulated phosphate fluoride and ceramic primer application; subgroup EP: conditioning with etch and prime only. Dual-cure adhesive resin cement (Multilink Automix) is utilized to adhesively bond the veneers. All specimens are subjected to 240,000 cycles of dynamic load aging prior to the fracture resistance test. The fracture resistance is measured in Newton (N). The Failure mode patterns are analyzed and categorized using a scanning electron microscope (SEM). The results are analyzed using a two-way ANOVA with Bonferroni's Post-Hoc test, followed by a one-way ANOVA for each factor. That is in addition to one-way ANOVA for surface treatment under each thickness, each followed by Bonferroni's Post-Hoc test. Then, a T-test is used to compare the two thicknesses under each surface treatment. All tests are set at 0.05 significance level. RESULTS: The two-way ANOVA test revealed that restoration thickness and surface treatment both significantly affect the fracture resistance values (p<0.05). The highest fracture resistance mean (2672±216N) is obtained from HF at 1.0 mm thickness, while the lowest mean (2104±299N) is obtained from APF at 0.5 mm thickness. CONCLUSION: All test groups, regardless of thickness, demonstrated fracture resistance values that exceeded both normal and parafunctional bite forces. The veneers that bonded after hydrofluoric acid etching followed by ceramic primer application showed more favourable fracture patterns.

Biting and thermal sensitivity relief of cracked tooth restored by occlusal veneer: A 12-to 24 months prospective clinical study.

OBJECTIVES: To analyze the relief time and risk factors of biting/thermal sensitivity in cracked tooth (CT) restored using occlusal veneer. METHODS: 63 CT were analyzed, and their demographic and clinical data and medical history were collected. Patients were followed-up to examine the relief of thermal/biting sensitivity. RESULTS: The maxillary first molar was the most prevalent (N = 25, 40%). The number of crack lines on the finish line ranged from 1 to 6 while the number of crack lines through preparation on the finish line from 0 to 4. Pain relief achieved steadily to 52% for thermal and 62% for biting at 1 week to over 90% for each by 3 months and was completely resolved (no pain) for each by 12 months. Painful of lateral percussion was related to a long period of thermal sensitivity (≥1 month) after restoration with occlusal veneer. The number of crack lines through preparation on the finish line >2 was correlated with biting sensitivity (≥1 month) post-treatment. CONCLUSIONS: Most patients (>90%) became asymptomatic of biting and thermal sensitivity within 3 months of CT restored by occlusal veneer. Lateral percussion and the number of crack lines through preparation on the finish line could be significant factors affecting postoperative symptoms. CLINICAL SIGNIFICANCE: Occlusal veneer is an ultrathin restoration and had no need for restricting clinical crown height, which could protect and relief the biting/thermal sensitivity of CT without preventive root canal therapy.

Management and prognosis of a vital cracked tooth by occlusal veneer for 14 months: A case report.

Key Clinical Message: An occlusal veneer is an ultrathin restoration method and a minimally invasive approach that can preserve more dental tissue and provide better aesthetic outcomes, thus increasing patient satisfaction. Abstract: An occlusal veneer is an ultrathin restoration method and a minimally invasive approach that can preserve more dental tissue and provide better aesthetic outcomes, thus increasing patient satisfaction; however, no previous studies reported on treating cracked teeth using occlusal veneer. Accordingly, we described the diagnosis and treatment process of a cracked tooth using occlusal veneer in a single case. A 29-year-old male presented at our dental clinic complaining of biting pain in the mandibular molar on the right-hand side. A routine oral examination with radiography was performed to evaluate the oral condition and treatment planning. The #16 tooth had a crack line surrounding the whole distal-lingual cusp from the occlusal surface. After discussing various therapeutic options with the patient, an occlusal veneer was performed. One week after treatment with occlusal veneer, the patient had no complaints. A 14-month follow-up showed promising clinical and radiographic outcomes. Occlusal veneer is an alternative treatment option for a cracked tooth, as it can preserve more dental tissue and potentially save pulp vitality.

The removal of three kinds of occlusal veneers by Er: Yag laser.

OBJECTIVES: This study aimed to remove occlusal veneers of varied thicknesses and compositions by Er:Yag laser in vitro and analyze the interfacial microstructure between veneers and tooth that irradiated by laser, by which experimental evidence could be provided to support the non-invasive removal of occlusal veneerby laser. METHODS: Fresh mandibular premolars extracted for orthodontic requirements were collected for tooth preparation. Three kinds of ceramic materials (Vita Suprinity, Vita Mark Ⅱ, and Upcera Hyramic) were selected to fabricate occlusal veneer with different thicknesses (1.0, 1.5, and 2.0 mm). One week later, Er:Yag laser (2.5 W and 3.5 W) was used to irradiate and remove the occlusal veneer and recorded the timespan. After the removal operation, the micro-morphologies of samples were examined by scanning electron microscope. RESULTS: Upcera Hyramic veneer failed to be removed (>20 min); the operation span at 2.5 W, Vita Suprinity (96.0 s±16.0 s) was longer than Vita MarkⅡ(84.5 s±19.5 s) in the 1.0 mm group (P<0.05), and Vita Suprinity (246.5 s±13.5 s) was longer than Vita MarkⅡ(170.0 s±14.0 s) in the 1.5 mm group (P<0.05). At 3.5 W, Vita Suprinity (381.0 s±24.0 s) was longer than Vita MarkⅡ(341.5 s±26.5 s) in the 2.0 mm group. CONCLUSIONS: Increasing laser power could shorten the operation span and facilitate the removal of occlusal veneers with the same thickness and composition. The occlusal veneer was sustained when insufficient laser power was applied. With the same laser power and ceramic thickness, laser penetration could interfere with the integral of the ceramic structure when the laser interacted with the bonding layer. With the same ceramic composition and laser power, the operation span and laser power increased with the thickness of the occlusal veneer. However, the laser was incapable of removing occlusal resin veneer directly.

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.

Influence of the preparation design on the survival probability of occlusal veneers.

OBJECTIVES: The fracture resistance of ultrathin computer-aided design and computer-aided manufacturing (CAD/CAM) occlusal veneers with different preparation designs was investigated under cycling mechanical loading and via finite element analysis (FEA). METHODS: Eighty molars were prepared with a circular enamel ring until complete exposure of the occlusal dentin occurred. Forty were prepared via additional circular chamfer preparation. The teeth were restored with 0.5 mm-thick occlusal veneers. Each group received a CAD/CAM fabricated occlusal veneer with a low modulus of elasticity (composite, CeraSmart) and a high modulus of elasticity material (ceramic, Celtra Duo). The restorations were adhesively luted and underwent 2000 thermocycling cycles. The samples were loaded at 50 N under 1,000,000 cycles in a chewing simulator and were checked for failure after various cycles. A visible crack was defined as failure, and the Kaplan-Meier survival rate was used for data analysis. One sample per group was digitized using microcomputed tomography, and FEA was performed using open-source software. The comparative stresses were analyzed for specimens with and without chamfer preparation. RESULTS: The survival probabilities were 60% for occlusal ceramic veneers without preparation and 40% for veneers with chamfer preparation, with no statistically significant differences. Composite veneers achieved 95% survival probability regardless of the preparation method. The main principal stress in ceramic restoration was visualized via FEA. In composite veneers, stress was also visible in the luting composite and dentin. SIGNIFICANCE: The preparation method had no influence on mechanical fatigue. Minimally invasive preparation can be recommended. The restoration material is crucial for survival.

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.

Effect of preparation design on the fracture behavior of ceramic occlusal veneers in maxillary premolars.

OBJECTIVES: The fracture strengths of four types of occlusal veneers and a traditional full crown ceramic restoration and the influence of preparation design on the stress of restorations were examined. METHODS: Forty intact maxillary premolars randomly divided into five groups were prepared based on the demands of type O (occlusal surface coverage), OF (occlusal and lingual surface coverage), POF (occlusal, lingual, and mesial surface coverage), and POFP (occlusal, lingual, mesial, and distal surface coverage) veneers and full crown, and then restored by glass ceramic. Specimens were subjected to fracture resistance tests after cyclic loading. The fracture strengths and modes were analyzed statistically. The level of significance was set at α = 0.05. One maxillary premolar was prepared for type O, OF, POF, POFP veneer and full crown, and then scanned to establish finite element models. The mean fracture load was applied vertically to calculate the maximum principal stress on the ceramic. RESULTS: Type O veneer showed higher fracture strength than type POF and POFP veneers (P < 0.05). Both type O and OF veneers exhibited higher fracture strength than full crown (P < 0.05). No significant difference in failure mode was observed. The maximum principal stress for type O, OF, POF, POFP veneers, and full crown increased progressively and concentrated at the bonding surface directly beneath the loading area. CONCLUSIONS: Four types of occlusal veneer showed fracture strengths that considerably exceeded normal biting forces. They represent conservative alternatives to full crowns and present a viable treatment for severely worn teeth. CLINICAL SIGNIFICANCE: The occlusal veneers with different preparation designs, including type O, OF, POF and POFP veneers, show higher fracture resistances than traditional full coverage crowns that considerably exceed the normal biting forces. Therefore, these represent conservative alternatives to crown restorations and present a viable treatment for restoring severely worn teeth.

Fatigue resistance of ultrathin CAD/CAM ceramic and nanoceramic composite occlusal veneers.

OBJECTIVE: The fracture resistance of different ultrathin occlusal computer-aided design/computer-aided manufacturing (CAD/CAM) veneers was investigated under cyclic mechanical loading to restore combined enamel-dentin defects. METHODS: Eighty-four molars were reduced occlusally until extensive dentin exposure occurred with a remaining enamel ring. Twenty-four molars were ground flat for examination of highly standardized specimens, of which 8 were treated with uniformly flat 0.3mm IPS Empress CAD and 0.3 and 0.5mm IPS e.max CAD restorations. Sixty-four molars were anatomically prepared until dentin exposure and were restored using occlusal veneers with fissure/cusp thicknesses of 0.3/0.5mm from 3 different dental CAD/CAM materials: IPS Empress CAD, IPS e.max CAD and Lava Ultimate CAD/CAM. Teeth were etched with 37% phosphoric acid, and occlusal veneers were bonded using an adhesive luting system (Syntac Primer, Adhesive, Heliobond and Variolink II). Specimens were placed under cyclic mechanical loading in a chewing simulator (1 million cycles at 50N) and were examined for cracks after each cyclic loading sequence. The anatomical 0.3/0.5mm IPS e.max CAD specimens experienced an additional 1 million cycles at 100N. Kaplan-Meier survival curves and log-rank tests were used for data analysis. RESULTS: All highly standardized and 0.3/0.5mm IPS e.max CAD specimens tolerated cyclic loading. One anatomical Lava Ultimate CAD/CAM and 10 IPS Empress CAD specimens showed cracks. SIGNIFICANCE: Ultrathin occlusal veneers of lithium disilicate ceramic and nanoceramic composite showed remarkably high fracture strength under cyclic mechanical loading. These veneers might be a tooth substance preserving option for restoring combined dentin-enamel defects.