Abstract: Objective: To investigate torque loss in the abutment screw of single posterior implant restoration at 10 minutes and 1 month after initial tightening of the screw in premolar or molar position with 4 different implant systems. Methods: From July 2021 to June 2023, 268 patients who underwent single posterior tooth implant surgery at the Implant Department of Peking University Shenzhen Hospital were transferred to the Prosthetic Department for restoration three months after the surgery. The patients were worn a cement-retained zirconia crown with an opening hole in the occlusal surface for the convenient of detachment. After adjustment, the central screws of the abutments were tightened through opening hole according to the preload suggested by the manufacturer. At 10 minutes and 1 month after the initial tightening, when tightening the central screw of the abutment again to the manufacturer’s suggested preload, the clockwise rotation angle of the torque wrench from the starting point to the end point was recorded. Results: At 10 minutes after the initial tightening, the rotation angle of torque wrench for all experimental groups was 0 degrees. However, at 1 month after the initial tightening, no matter which group, tooth, or implant, the rotation angle of torque wrench was greater than 0 degrees. Among them, 29 cases (10.82%) were greater than 90 degrees, however, no significant differences were found between groups (P>0.05). No case reached or exceeded 180 degrees. Conclusion: In some implant systems, 1 month after a single posterior implant restoration, the loss of torque in the central screw of the abutment is more significant in some cases, and the proportion is not related to whether the central screw of the abutment has been tightened again 10 minutes after the initial tightening, as well as the premolar or molar site and the implant system used.

Key words: torque loss, retightening, settling effect, dental implant restoration, abutment screw