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

Abstract

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

Materials and methods: A total of 60 implant-abutment assemblies were divided into three groups that each simulated different levels of frictional resistance as follows: (1) low: < 30 Ncm; (2) medium: 30 to 40 Ncm; and (3) high: > 40 Ncm. The endpoint for abutment screw tightening was 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 analysis of variance (ANOVA) and post-hoc Tukey tests were used.

Results: For all frictional resistance groups, abutment screws tightened with a counter-torquing device attained 35 Ncm (P > .05). Abutment screws tightened without a counter-torquing device in low and medium frictional resistance groups 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 > .05) but were significantly different in the low frictional resistance group (P < .001). No significant difference was found for the change in implant angular displacement for all groups (P > .05), regardless of counter-torquing measures; however, a high variance was observed in the low and medium frictional resistance groups.

Conclusions: Under the experimental conditions, counter-torque is important to ensure that 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.