a special design to facilitate retrieval of cement-retained zirconia-based implant-supported restorations

Statement of the problem: retrieval of cementretained implant-supported restorations is challenging in cases of screw loosening or periodontal problems. purpose: the purpose of this study was to evaluate the effect of the screw access hole on the fracture resistance of zirconiabased cement-retained restorations with and without an access opening. materials and method: in this in vitro study thirty-three cementretained implant-supported zirconia-based molar crowns were fabricated and divided into 3 groups (n=11). as the control group, group 1 consisted of conventional cement-retained crowns. group 2 comprised conventional cement-retained crowns in which a hole was created in the location of the screw. group 3 consisted of cement-retained crowns in which a ledge was created in the location of the screw access channel. the specimens were cemented to their abutments and their access openings were filled with composite resin. a compressive load was applied to the specimens using a universal testing machine until they fractured. the mean fracture resistance values of the samples were compared by using the oneway anova and tamhane posthoc test (a=0.05). results: the mean fracture resistance values were 1270.18± 12.67 n in group 1 (the control group), 960.09±210.67 n in group 2 (conventional), and 1357.81±361.68 n in group 3 (the special design). the fracture resistance value was higher in the special design group than that of the conventional design (p = 0.018) and the fracture resistance value of the conventional design group was less than that of the control group (p = 0.042). no statistically significant difference was detected between the control group and the special design group in fracture resistance values. conclusion: preparing a screw access hole in cement-retained implant-supported zirconia-based crowns decreased the fracture resistance of the restoration. designing a ledge in the zirconia framework around the access hole may increase the fracture resistance of the restoration.