The Effect of Angulation of The Abutment, and Tightening Torque Protocols on Abutment Screw Loosening

The present study assesses the effect of angulation of the abutment, location of the implant, and tightening torque protocols on abutment screw loosening. Implant-abutment complexes (n=168) were obtained and assigned into three groups regarding abutment angulations (parallel, 15°, and 25° for abutments). The groups were reassigned to two groups: once up to 30 N/cm or twice up to 30 N/cm, with a 10-minute interval between the first and second torque applications. The implants were mounted into autopolymerizing acrylic resin. After thermocycling, the groups were divided into two subgroups subjected to compressive forces of 120 N or 90 N, with a 30° angulation relative to the implant’s longitudinal axis. The specimens were placed in the masticatory simulation device; and subjected to 500000 cyclic loadings simulating 6 months of clinical service. The effects of the variables on the detorque values were analyzed using a three-sided analysis of variance, and the paired comparisons between groups with different abutment angles were performed using Tukey's post hoc test. The torque application times, loads applied, and the interaction between torque times and load values, as well as the interaction between torque times and abutment angulations, and the interaction between torque times, loads, and abutment angulations, had no significant effect on the detorque values of the abutment. However, abutment angulations (p<0.001) and the interaction between the applied loads (p=0.027) affected the detorque values. Detorque values decreased with increased abutment angulations after cyclic loading.