Effect of Abutment Connection Type and Cyclic Loading on Removal Torque Value

Maintaining the primary torque of the abutment screw is a common problem related to implant-supported restorations; a failure in this respect often leads to screw loosening. The abutment screw plays a critical role in the long-term stability of restorations. This study aimed to assess the effect of two abutment connection types with and without cyclic loading on removal torque value (RTV). A total of 24 abutments and fixtures were evaluated in this in-vitro experimental study. Two abutments with internal and external connections were tightened to fixtures using a digital torque-meter according to the manufacturer's instructions. Half of the samples were subjected to cyclic loading with a 100-N mechanical load at a 1-Hz frequency (500,000 cycles) applied at 23±1°C with 50±5% humidity. Next, the RTV was measured for each abutment. Two-way analysis of variance (ANOVA) was used to assess the effect of the abutment system and cyclic loading on RTV. The highest RTV belonged to the internal connection abutment without cyclic loading (22 Newton-centimeter (Ncm)), while the lowest RTV was noted with the external connection abutment subjected to cyclic loading (14 Ncm; P<0.01). There was no statistically significant interaction effect between the two variables (the abutment system and cyclic loading; P=0.839). The RTV in the internal hexagon abutments was significantly higher than that in the external hexagon abutment system (P<0.001). Cyclic loading significantly reduced the RTVs in both abutments (P<0.001). According to the results, internal connection abutments experience less screw loosening.