Screw Retained Implant Supported Zirconia Anterior Fixed Dental Prosthesis with Different Abutment Angulations: Evaluation of Fracture Resistance and Failure Modes

Objective: To evaluate the effect of different implant-abutment angulations on the fracture resistance of anterior three-unit implant-supported zirconia fixed dental prosthesis. Materials and Methods: Five groups (n=10) were fabricated to represent maxillary anterior three-unit zirconia fixed dental prosthesis supported by two implants with different implant-abutment angulations including group 0^o-0^o, group 0^o-17.5^o, group 0^o-35^o, group 17.5^o-17.5^o and group 35^o-35^o. Zirconia FDPs were cemented by self-adhesive resin cement. All specimens were subjected to thermocycling (5000 X 5^oC/55^oC) and mechanical loading (50 N X 120,000 cycles /1.6Hz). Static loading was applied using the universal testing machine at a crosshead speed of 1 mm/min. One-way ANOVA and Post hoc Tukey test were applied and statistical significance was set at P value < 0.05. Results: All specimens subjected to TCML survived without mechanical failure. Group 0°-35°, group 17.5°-17.5° and group 35°-35° (654.24 ± 81.66 N; 551.34 ± 87.79 N; 382.42 ± 52.07 N, respectively) showed a significant decrease in fracture resistance compared to that in group 0°-0° which showed the highest fracture resistance (759.72 ± 88.33 N) (P=0.04, <0.001, <0.001 respectively). There was no significant difference between group 0°-17.5° (746.04 ± 85.02 N) (P=0.99) compared to that in group 0°-0°.Conclusions: The fracture resistance of zirconia FDPs decreased as implant-abutment angulation increased. Angled abutments of 0^o, 17.5^o, and 35^o could be used as a suitable option for restoration of nonideally placed implants but within limitations, because there was a significant decrease in fracture resistance in group 17.5°-17.5° and group 35°-35°.