Full-contour zirconia restorations without porcelain veneering were introduced into the clinical use to avoid chipping or fracturing of the veneer. The purpose of this study was to evaluate the failure load of posterior full-contour four-unit fixed partial dentures (FPDs) after mechanical fatigue testing and artificial ageing.
Method:
A total of 30 identical four-unit FPDs were milled from biscuit-sintered zirconia blanks (inCoris TZI, Sirona, Germany) in an anatomic, full-contour design, sintered and glazed. They were divided into three groups of 10, cemented onto a fixture made of an artificial bone mimicking the real clinical situation, and loaded occlusaly in a three-point bending mode using a universal testing machine. The control group was monotonically loaded to fracture; the second group was dynamically loaded in water (0–300N, 106 cycles) prior to fracture, while the third group was first subjected to accelerated ageing (in a diluted acetic acid solution at 134 °C for 12 hours), than to mechanical fatigue and finally monotonically loaded to fracture. One-way ANOVA and Bonferroni post-hoc test were used to compare data at a level of 5%.
Result:
Two tested FPDs did not survive 106 cycles of dynamic loading, one in Group 2 and one in Group 3. The failure load values (N) were Group 1(control): 547.3±66.3, Group 2 (n=9): 465.2±118.0, and Group 3 (n=9): 408.8±58.9. Using ANOVA (p≤0.05), a statistically difference was found between Group 1 and Group 3. No statistical significance was found between Group 1 and Group 2, and between Group 2 and Group 3.
Conclusion:
Dynamic loading reduces fracture resistance of full-contour zirconia FPDs especially in combination with accelerated ageing. Nevertheless, the fracture loads were high indicating that full-contour zirconia restorations are an interesting alternative to veneered zirconia and metal-ceramic restorations in posterior region.