Purpose: Abutment screw loosening is a frequently encountered prosthetic complication in implant dentistry. Due to the detection of preload loss soon after initial torque application, abutment screw retightening 10 minutes after initial tightening has been recommended. The aim of this clinical study was to assess preload maintenance in the abutment screws of single posterior implants after 1 month of use by employing screw-cement-retained prostheses and a clinical assessing method, with the ultimate goal of helping to improve the clinical workflow of implant-based restorations.
Materials and Methods: In total, 158 patients treated using three implant systems were divided randomly into two groups in which abutment screws were and were not retightened, respectively, approximately 10 minutes after initial torque application. Screw-cement-retained prostheses, which permitted the assessment of abutment screw preload maintenance and screw retightening after 1 month of use, were used. Preload loss at 1 month was defined as the failure to achieve the torque recommended for the abutment screws after 90-degree clockwise rotation of the screwdriver. The data were analyzed using binary logistic regression, with a significance level of P ≤ .05.
Results: No preload loss was detected 10 minutes after initial screw tightening. Preload loss was detected in 16 (10.13%) cases at 1 month after initial tightening, with no significant difference according to the implant system used, the presence or absence of retightening at 10 minutes after initial tightening, or implant position (premolar or molar).
Conclusion: Under the experimental conditions of this study, abutment screws in some bone-level, internal tapered–connection, platform-switching implant systems showed preload loss at 1 month after abutment placement for single posterior implant-based restorations, regardless of implant system or whether abutment screws had been retightened 10 minutes after abutment placement, or implant position (premolar or molar). It is necessary to retorque the abutment screws 1 month after initial torque. The screw-cement-retained prostheses used in this study permit abutment screw retightening at that time and have advantages over traditional methods.
Keywords: dental implant, dental prosthesis, preload, settling effect, torque
