Clinically available preload prediction based on a mechanical analysis

Abstract

Screw loosening, which is closely associated with the preload of an abutment screw, is one of the most frequent complications in clinical implantology. The aim of the present study was to investigate the preload prediction of a joint screw assembly between an implant and abutment based on a mechanical analysis. A mechanical formula was determined to relate preload, the dependent variable, to the tightening-loosening torque difference, the independent variable. To confirm the equation, 15 implant-abutment assemblies were prepared. These assemblies were divided into five groups based on tightening torques, and joint screw loosening torques were recorded. Preload values of the assemblies were calculated using a mechanical formula and compared with those previously obtained from direct measurements. In addition, the recommended tightening torque was deduced to prevent screw loosening using the linear relation between tightening torque and the tightening-loosening torque difference. Theoretically calculated preload values were similar to those directly estimated using devices to measure preload. Every predicted preload was insufficient in preventing screw loosening. However, the theoretical preload for prevention was clinically unavailable. These results indicate that prevention of screw loosening requires repeated tightening of the abutment screw. Moreover, this study suggests a useful tool to predict preload, which was practically applicable to the implant-abutment assembly, in dental implantology.