Effect of screw access hole preparation on fracture load of implant-supported zirconia-based crowns: an in vitro study

Background. fracture load of implant-supported restorations is an important factor in clinical success. this study evaluated the effect of two techniques for screw access hole preparation on the fracture load of cement-screw-retained implant-supported zirconia-based crowns. methods. thirty similar cement-screw-retained implant-supported zirconia-based maxillary central incisor crowns were evaluated in three groups of 10. group nh: with no screw access holes for the control; group hbs: with screw access holes prepared with a machine before zirconia sintering; group has: with screw access holes prepared manually after zirconia sintering. in group hbs, the access holes were virtually designed and prepared by a computer-assisted design/computer-assisted manufacturing system. in group has, the access holes were manually prepared after zirconia sintering using a diamond bur. the dimensions of the screw access holes were equal in both groups. the crowns were cemented onto same-size abutments and were then subjected to thermocycling. the fracture load values of the crowns were measured using a universal testing machine. data were analyzed with anova and tukey test (p < 0.05). results. the mean fracture load value for the group nh was 888.37 ± 228.92 n, which was the highest among the groups, with a significant difference (p < 0.0001). the fracture load values were 610.48 ± 125.02 n and 496.74 ± 104.10 nin the hbs and has groups, respectively, with no significant differences (p = 0.44). conclusion. both techniques used for preparation of screw access holes in implant-supported zirconia-based crowns decreased the fracture load.