Fracture strength and energy-dispersive spectroscopy analysis of 3-unit fixed partial dentures fabricated from different monolithic zirconia materials.

STATEMENT OF PROBLEM: Mastication forces in different regions affect the survival of multiunit posterior restorations. The fracture strength of 3-unit posterior monolithic zirconia fixed partial dentures (FPDs) and their fracture patterns require investigation. PURPOSE: The purpose of this in vitro study was to evaluate and compare the fracture strength and fracture pattern of 3-unit posterior FPDs fabricated from different monolithic zirconia materials. MATERIAL AND METHODS: Thirty 3-unit FPDs were fabricated from BruxZir, FireZr, and Upcera (n=10 per group). Energy-dispersive spectroscopy analysis was performed on 2 selected specimens from each group. All specimens were exposed to a mastication simulator for 1.2x10(6) cycles and then monotonically loaded to fracture at a crosshead speed of 1 mm/min. The surfaces of a selected fractured specimen were examined at magnifications of x25 and x500 with scanning electron microscopy. Conformity to normal distribution was evaluated with the Shapiro-Wilk test. One-way analysis of variance was used to compare the normally distributed initial crack formation load F initial (F(i)) and catastrophic failure strength F maximum (F(m)) means by group. Weibull statistics were calculated by using the maximum likelihood estimation method. The chi-square test was used to compare shape and scale parameters (alpha=.05). RESULTS: The mean F(m) values were fail1878.9 N for Upcera, 2177.8 N for BruxZir, and 2229.4 N for FireZr. Upcera and BruxZir showed statistically significant differences for the F(m) mean values (P=.039). The differences between the fracture type distributions according to the groups were statistically similar (P>.05). For F(i,) Upcera presented the highest Weibull modulus value (2.199), FireZr had the lowest (1.594), while for F(m,) BruxZir had the highest Weibull modulus value (9.267) and FireZr the lowest (6.572). CONCLUSIONS: Using the zirconia materials BruxZir, FireZr, and Upcera resulted in high F(m) values after aging procedures. With all materials, the fractures were most commonly found in the connector areas in the tested FPDs.