Although the reduction in RTVs was observed after mechanical cyclic loading, no screw loosening occurred after 2,000,000 cycles of loading, which it assumed represents 3 years of function in worse scenario setting according to ISO 14801 in vivo [23]. Our study presents similar results to those of Binon and McHugh, who reported that the 30-N-cm insertion torque can maintain screw-joint stability in 3 years of simulated function [34]. The reduction of screw preload after 2,000,000 cycles of loading was 42.74%. This is considered to be relatively low and might be because of the implant-abutment connection design [39]. The eccentric force has little effect on the screw preload under functional loading because the contacting part of the cone connection helps to provide frictional resistance and mechanical stability [7, 8]. Moreover, the Octatorx lobular anti-rotational design help produce little micromovement in the joint system under load [9]. The screw design also has an effect on the screw preload [39]. Paepoemsin et al. [31] found that the retaining tapered screws of their implants maintained higher preload efficiency than did the flat head screws of the implants before and after cyclic loading (P < 0.05). In our study, RTVs were constant from 50,000 cycles of loading to 1,800,000 cycles. This result is not in agreement with those of Khraisat et al. [40], who concluded that 1,000,000 cycles of loading significantly affected the RTVs of CeraOne abutment external hex implants compared with 500,000 cycles of loading. This might be because different types of implant-abutment connections were used. In external connections, implant-abutment stability is obtained primarily by the tension of the screws [4]. Therefore, the screw preload in external connections is affected by the cyclic loading more than in internal connections.

Cho et al. [39] studied the effect of retightening the abutment screw on RTVs in internal connection implants under cyclic loading at 3, 10,100, and every 20,000 cycles up to 100,000 cycles. They found that most of the decrease in RTVs occurred at 10 cycles, and after that, RTVs did not change significantly. The study showed that retightening the abutment screw under cyclic loading resulted in superior RTVs when compared with no retightening [39]. However, retightening the abutment screw might change the shape of the abutment screw and the inner screw thread of the implant [41]. In our study, we demonstrated decreasing the RTVs after cyclic loading without retightening the abutment screw.