Fatigue behavior of zirconia-ceramic, galvano-ceramic, and porcelain-fused-to-metal fixed partial dentures.

PURPOSE: This study evaluated the fatigue behavior of three fixed partial dentures (FPDs) before and after artificial fatigue testing. MATERIALS AND METHODS: Sixty, three-unit zirconia-ceramic (ZC), galvano-ceramic (GC), and porcelain-fused-to-metal (PFM) FPDs (N = 20) were fabricated. Ten specimens from each group were exposed to fatigue testing by being thermocycled (5 to 55°C, 10,000 cycles) and loaded (100,000 cycles, 50 N, 0.5 Hz). All specimens were then subjected to occlusal loading in a universal testing machine until fracture. The fractures were characterized using scanning electron microscopy. Data were analyzed using one-way ANOVA followed by Tukey's significant difference post hoc test and the paired t-test. The chi-squared test was used to evaluate the type of fracture (α = 0.05). RESULTS: The mean fracture loads of non-fatigued and fatigued specimens for ZC were 2434.9 ± 154.3 and 2333.1 ± 183.0 N, respectively; for GC were 1678.1 ± 211.6 and 1475.8 ± 227.9 N, respectively; and 1878.5 ± 176.5 and 1687.8 ± 162.2 N, respectively, for PFM restorations. Significant differences were observed between fatigued and non-fatigued specimens of both the GC group and PFM group (p < 0.05), but not between fatigued and non-fatigued ZC specimens (p > 0.05). Differences between the PFM and GC specimens were not statistically significant for fatigued or non-fatigued specimens (p > 0.05). Fracture types did not differ significantly among groups. CONCLUSIONS: ZC specimens were not significantly affected by fatigue, whereas GC and PFM specimens were affected. All tested restorations have the potential to withstand occlusal forces applied in the posterior region.

Evaluation of the retention force of double conical crowns used in combination with a galvanoforming and casting fabrication technique.

PURPOSE: The aim of this study was to measure the in vitro retention force of double conical crowns fabricated using primary galvanoforming and secondary casting techniques and those fabricated using primary casting and secondary galvanoforming techniques under simulated clinical conditions before and after a wear test. MATERIALS AND METHODS: Primary galvanoformed crowns (n = 10) with non-noble secondary crowns (n = 10; group A) and primary non-noble crowns (n = 10) with secondary galvanoformed crowns (n = 10; group B) were fabricated. Each primary and secondary crown was embedded in acrylic resin and weighed with a digital balance. Retention forces were then measured using a universal testing device. To simulate wear, specimens were inserted and separated horizonatally 3285 times in wear equipment with artificial saliva. Retention forces and weights of the double crowns were then remeasured. Data were analyzed using paired t-tests and Wilcoxon tests, and the groups were compared using Mann-Whitney U-tests. RESULTS: In group A, the wear test had a significant influence on the retentive force (p < 0.05), but wear produced no significant difference in weight (p > 0.05). In group B, the wear test had a significant influence on the retentive force (p < 0.05), and wear produced a significant difference in weight (p < 0.05). CONCLUSIONS: The results of this study indicated that the use of different combinations of galvanoforming and casting techniques in the fabrication of conical crowns significantly affected retention force.

The effect of dentin desensitizer with different layers on thermal changes on the pulp during fabrication of provisional restoration.

PURPOSE: This study investigated the effects of different desensitizers and an adhesive material application on pulpal temperature rise during direct provisional restoration polymerization. MATERIALS AND METHODS: Two dentin desensitizers (Systemp, Ivoclar; BisBlock, Bisco) and a dentin adhesive (Prime Bond, Dentsply) were applied to the dentin surfaces as single layer or double layer. One autopolymerizing methacrylate (Prevision, Heraeus Kulzer) and one light polymerizing composite (Revotek LC, GC) provisional restoration materials were used in this study. A total of 160 dentin disks were prepared from extracted molars. These dentin disks were placed on an apparatus developed to measure temperature rise. After the desensitizer or dentin adhesive application, provisional materials were polymerized according to the manufacturers' instructions. The temperature increase was measured under the dentin disk with a J-type thermocouple wire that was connected to a data logger. Differences between initial and highest temperature reading were taken, and 10 readings were averaged to determine the mean value in temperature rise. Statistical analysis was performed with three-way analysis of variance followed by Tukey HSD test (alpha = 0.05). RESULTS: Temperature rise varied according to the provisional restoration material used (composite resin, methacrylate) (p < 0.001), the agent thickness (single, double) (p < 0.001), and the agent (desensitizer, adhesive) (p < 0.001). The composite resin-based provisional material induced higher thermal changes than methacrylate based provisional material (p < 0.01). CONCLUSION: The thickness of desensitizing agents affected the thermal changes; however, the desensitizers did not affect on the intrapulpal temperature although the type of provisional material used may be effective.