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 machinery 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. the data were statistically analyzed using anova and tukey’s test (p<0.05). results: the mean fracture load value for the group nh was 888.37±228.92 n, which was significantly the highest among the groups (p<0.0001). the fracture load values were 610.48±125.02 n and 496.74±104.10 n for the group hbs and has respectively, with no significant difference (p=0.44). conclusions: both used techniques for preparation of screw access holes in implant-supported zirconia-based crowns decreased the fracture load.