Effect of screw access hole design on the fracture resistance of implant-supported zirconia-based restorations.

OBJECTIVE: To evaluate the effect of screw access hole design on the fracture resistance of cement-retained implant-supported zirconia-based restorations with screw access holes. MATERIALS AND METHODS: Thirty cement-retained implant-supported zirconia-based molar crown specimens were fabricated. The specimens were divided into 3 groups of 10: without access holes (C), with screw access holes (S), and with screw access holes accompanied with a surrounding zirconia wall (W). The veneering ceramic thickness was 0.8 mm in all groups. Implants were vertically mounted in a metal block. Abutments were screwed on the implants and the specimens were cemented to the abutments. A universal testing machine applied compressive forces to the specimens until fracture. Fracture resistance values of the specimens were measured. One-way analysis of variance (ANOVA) and Tukey HSD tests were used to analyze data (P < .05). RESULTS: The mean fracture resistance values were 5794.85 N for C, 2691.48 N for S, and 3878.06 N for W. The screw access hole design significantly affected the fracture resistance (P < .0001). Significant differences were found between C and S (P < .001), C and W (P < .001), and S and W (P = .026). CONCLUSIONS: The screw access hole decreased the fracture resistance. A surrounding zirconia wall for the screw access hole increased the fracture resistance. CLINICAL SIGNIFICANCE: Screw access hole design may affect the fracture resistance of cement-retained implant-supported zirconia-based restorations with screw access holes. This study introduced a screw access hole design to improve the fracture resistance of these restorations.