Fracture strength of veneer contact lens

The no prep technique to ceramic veneer have some advantages, one of the most important is the preservation of tooth structure. Purpose: Evaluate fracture resistance in bovine teeth, of ceramic veneer in different thickness (0,3 to 1,0mm). Methods: 60 teeth were selected for this study. Forty fifth ceramic veneer were made for each tooth, variating the thickness in: G1 ­ 0,7mm; G2 ­ 0,5mm; G3 ­ 0,3mm and G4 ­ 1,0mm (control group). Flexural strength test was carried out after 24h of luting. The results were analysed by ANOVA and HSD of Tukey. Results: the results showed that was no statistic difference between the groups (G1- 297.2200; G2 - 294.5467; G3 - 291.9380 and G4 -290.0733). Conclusion: The ceramic veneer thickness didn't have influence in the final flexural strength.

Influence of silanes on the stability of resin-ceramic bond strength.

PURPOSE: To evaluate the in vitro stability of resin-ceramic bond strength provided for silanes with acidic functional monomers. METHODS: Five ceramic blocks were fabricated. The blocks were randomly divided into groups (n=30) and assigned to the following surface treatments: ( C) HF + RelyX Ceramic Primer, ( G1) HF + Porcelain Liner M, ( G2) HF + Clearfil Ceramic Primer, ( G3) Phosphoric acid ( H3PO4) + Clearfil Ceramic Primer, ( G4) H3PO4 + Porcelain Liner M. Two adhesives were used: Single Bond in Group C and Clearfil SE Bond in the other groups, after which, each block received four 1 mm increments of resin composite Filtek Z350. The resin-ceramic blocks were sectioned, obtaining samples of approximately 0.8 mm + à¡© 0.8 mm. The groups were subdivided according to aging mode: I - immediate ( 24 hours storage in artificial saliva) and A - aged ( 3 months in artificial saliva + 5,000 thermal cycles 5°C/55°C). The microtensile test was performed with a 0.5 mm/minute crosshead speed ( n = 15) on a universal testing machine. The fracture patterns were categorized with scanning electron microscopy. The results were analyzed using three-way ANOVA and Tukey's test ( P≤ 0.05). RESULTS: Silanes containing acidic functional monomers did not affect the stability of the resin-ceramic bond strength. The use of HF acid was a necessary condition for stability. The highest values after aging were obtained by silanes with functional molecules without a statistically significant difference. The storage influenced the values of bond strength. The use of acidic functional monomers did not affect the resin-ceramic bond after storage in saliva followed by thermal cycling. CLINICAL SIGNIFICANCE: Silane agents containing acidic functional monomers did not influence the stability of the resin-ceramic bond. The use of hydrofluoric acid is recommended to provide stability of the bonds.

Fatigue resistance of ultrathin CAD/CAM complete crowns with a simplified cementation process.

STATEMENT OF PROBLEM: Traditional tooth preparation for complete crowns requires a substantial amount of hard tissue reduction. This is in contrast with the principles of minimally invasive dentistry. An ultrathin complete crown preparation is proposed instead. PURPOSE: The purpose of this in vitro study was to assess the fatigue resistance and failure mode of computer-aided design and computer-aided manufacturing (CAD/CAM) ultrathin complete molar crowns placed with self-adhesive cement. Different restorative materials (resin nanoceramic [RNC], feldspathic ceramic [FEL], and lithium disilicate [LD]) were compared. MATERIAL AND METHODS: Forty-five extracted molars with a standardized crown preparation were restored with the Cerec 3 CAD/CAM system using FEL, LD, or RNC (n=15). FEL and LD restorations were etched with hydrofluoric acid and silanated. RNC restorations and all preparations were treated with airborne-particle abrasion. All restorations (thickness=0.7 mm) were cemented with RelyX Unicem II Automix cement and submitted to cyclic isometric loading, beginning with a load of 200 N (5000 cycles) and followed by stages of 400, 600, 800, 1000, 1200, and 1400 N at a maximum of 30 000 cycles each. The specimens were loaded until failure or for a maximum of 185 000 cycles. The failure mode was categorized as "catastrophic," "possibly reparable," or "reparable." The groups were compared using life table survival analysis (log rank test at α=.05). Previously published data from the same authors about traditional complete crowns (thickness 1.5 mm) using the same experimental design were included for comparison. RESULTS: All specimens survived the fatigue test until the 600 N step. RNC, LD, and FEL failed at an average load of 1014 N (1 survival), 1123 N (2 survivals), and 987 N (no survivals), and no difference in survival rate was found. No catastrophic failures were reported after the fatigue test. Comparison with previously published data showed that 1.5-mm thick complete crowns demonstrated higher survival rates than the ultrathin restorations, independent of the material. CONCLUSIONS: The fatigue resistance of ultrathin complete molar crowns (placed with a simplified cementation process) made of RNC, LD, and FEL was not significantly different. All materials survived the normal range of masticatory forces. All failures were re-restorable. Regular crowns of 1.5 to 2.0 mm thickness may present higher survival rates than ultrathin ones.

Fatigue resistance of CAD/CAM complete crowns with a simplified cementation process.

STATEMENT OF PROBLEM: Various computer-aided design and computer-aided manufacturing (CAD/CAM) materials are available to fabricate complete crowns. The type of material may have an effect on the longevity of these restorations. PURPOSE: To evaluate the fatigue resistance, load-to-failure, failure mode, and antagonistic wear of complete molar computer-aided design and computer-aided manufacturing (CAD/CAM) crowns made of resin nanoceramic (RNC), feldspathic glass ceramic (FEL), or lithium disilicate (LD) placed with a simplified cementation process. MATERIAL AND METHODS: Forty-five molars received a standardized complete crown preparation and were restored with CAD/CAM crowns (1.5-mm thickness, n=15) made of RNC, FEL, and LD. After cementation, the restorations were submitted to cyclic isometric loading: 200 (×5000), 400, 600, 800, 1000, 1200, and 1400 N at a maximum of 30 000 cycles each. Surviving specimens were axially loaded until failure or to a maximum load of 4500 N. The specimens were analyzed as to failure mode: catastrophic, possibly repairable, and repairable. The groups were compared by using the life table survival analysis and the t test (α=.05). RESULTS: All the specimens survived the fatigue process until the 800-N step. The survival rate of RNC was 80%, LD 93.3%, and FEL 6.6%. The survival of RNC and LD crowns did not differ from each other but exceeded that of FEL. Postfatigue load-to-failure test was 2500 N (FEL), 3122 N (RNC), and 3237 N (LD). No catastrophic failure occurred in the fatigue test, whereas all of the specimens in the load-to-failure test exhibited catastrophic fractures. Crowns made of RNC seemed to generate the least amount of antagonistic wear. CONCLUSIONS: Posterior crowns made of RNC and LD were not statistically different, and both had significantly higher fatigue resistance than FEL. All materials survived beyond the normal range of masticatory forces, and all failures were possibly re-restorable except those in the load-to-failure test. RNC crowns seemed to cause less wear of the antagonist.