Background and Aim: 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).
Materials and Methods: 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. 
Results: 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).  
Conclusion: According to the results, internal connection abutments experience less screw loosening.