The Effect of Bar Design and Repetitive Loading on the Reverse Torque Values of Lateral Set Screws

Abstract

Statement of problem: Utilizing set screws allows easy retrieval of the prostheses with minimum cost and satisfies esthetic requirements. Set screws use is mostly governed by retrospective, anecdotal and clinical reports. The purpose was to investigate the difference in reverse torque values of fatigued one set screw or two set screws used to retain straight or curved implant prostheses in vitro. Materials and methods: Milled substructures (straight and curved) and cast superstructures retained by one or two set screws were used. There were four groups (n=8). Set screws were tested for changes in reverse torque values after simulated chewing of six months. Data (Ncm) was analyzed using 2-way ANOVA (p≤0.05). Results: No statistically significant difference in the reverse torque values between prostheses retained by one set screw and two set screws (F = 0.18, p = 0.67) or between prosthesis retained on curved bars and straight bars (F = 0.42, p = 0.52). No significant interaction was found in the reverse torque values between the number of set screws and substructure design (F = 0.32, p = 0.58). Conclusions: Under functional loading the reverse torque values are not affected by the design of the prosthesis or the number of set screws used to retain the prosthesis.