Effect of screw access channel on the fracture rate of lithium disilicate cement-retained implant-supported posterior crowns

Statement of problem Whether the presence of a screw access channel on the occlusal surface of a lithium disilicate cement-retained single tooth implant restoration reduces its fracture rate is unclear. Purpose The purpose of this randomized controlled clinical trial was to compare the fracture rate of lithium disilicate cement-retained posterior single tooth implant restorations with or without screw access channels. The study also evaluated whether the crown dimensions and location of the occlusal screw access channel would affect the fracture rate. Material and methods A split-mouth study was conducted where 40 participants having 2 implants placed to restore single missing posterior teeth with crowns were enrolled. Implants were randomly allocated into a conventional crown group or a screw access group, receiving cement-retained restorations fabricated from lithium disilicate glass-ceramic with and without an occlusal screw access channel. Crown dimensions were recorded in millimeters from the designing software. Follow-up evaluations were made at 3, 6, and 12 months by observing visible cracks or fractures of the crowns. The Kolmogorov-Smirnov test of normality was used. Comparisons were carried out by using the Student and Welch t tests (α=.05). Results After a 12-month follow-up period, no crowns fractured or revealed visible cracks, resulting in a 100% success rate. No statistically significant differences were found between the conventional crown group and screw access channel group in all crown dimensions (P>.05). Conclusions The presence of an occlusal screw access channel did not affect the short-term fracture rate of lithium disilicate cement-retained single implant–supported posterior crowns. The amount of axial cantilever, occlusal ceramic thickness, and location of the screw access channel on the occlusal surface of the restoration have no effect on its fracture rate.