An In Vitro Study of Torque Application in Abutment Screw Tightening at the Implant-Abutment Junction in Simulated Osseointegrated Implants.

Purpose: To evaluate initial and removal torque values (ITV and RTV) in abutment screw tightening and their impact on torque application at the implant-abutment junction (IAJ), utilizing a biomechanical friction resistance model simulating various bone densities, with and without counter-torquing measures.

Materials and method: Sixty implant-abutment assemblies were divided into three groups, each simulating different levels of frictional resistance. The endpoint for abutment screw tightening were either reaching a preset torque value of 35 Ncm or detecting a change in the implant's angular position. ITV, RTV, and changes in angular position were recorded. One-way ANOVA with Tukey post hoc were used.

Results: For all frictional resistance groups, abutment screws tightened with a counter-torquing device attained 35 Ncm (p> 0.05). Abutment screws tightened without a counter torquing device in low and medium frictional resistances were unable to attain 35 Ncm prior to implant rotation. ITVs of abutment screws without counter-torque were not significantly different in the medium and high frictional resistance groups (p > 0.05), except in the low frictional resistance group (p < 0.001). No significant difference in the change in implant angular displacement for all groups (p > 0.05) regardless of counter-torquing measures; however, a high variance was observed in the low and medium frictional resistance groups.

Conclusion: Under the experimental conditions, counter-torque is important to ensure the desired torque value is applied to the implant-abutment connection in low frictional resistance. RTV is proportionally related to ITV and can be used to estimate the ITV at the IAJ.