The effect of laboratory debris contamination on reverse torque of implant abutment screws

Abstract

Introduction: Loosening of the abutment screw is one of the most common complications after treatment in dentures based on dental implants. One of the main reasons for abutment screw loosening is the loss of preload. Among these, the settling effect plays the most important role in the loss of preload, which is mainly due to the wear and smoothing of microscopic points causing friction in the joint area. If a part of the applied torque is used to overcome the friction caused by the rough components of the joint area, of course, the amount of force remaining to create preload will be reduced and the possibility of abutment screw loosening will increase. Since no study has been performed on the effect of laboratory debris on the reverse torque of dental implant abutment screw, the aim of this study was to evaluate the possible adverse effects of these debris in terms of biomechanics. Materials and methods: Sixteen implants were examined in this study. Half of the abutments were sent to the laboratory before being placed on the fixture to make all-ceramic prostheses with zirconia cores, and the other half of the abutments were placed on the relevant fixtures without any changes or cleaning. The applied torque was measured using a digital torque meter and then a reverse torque was applied and its amount was measured. For statistical analysis of data, Mann-Whitney test was performed by SPSS software version 17 and a significance level of p≤0.05 was considered. Results: The amount of reverse torque in non-contaminated condition (16.63 ± 2.39) was significantly higher than the amount of reverse torque in contamination with laboratory debris (12.75 ± 1.98) (p <0.05). And the difference between torque and reverse torque in contamination with laboratory debris (13.5 ± 2.20) is significantly greater than the difference between them in non-contaminated condition (8.37 ± 2.55) (p <0.05). Conclusion: Contamination of the implant abutment screw with laboratory debris significantly reduces its reverse torque compared to the primary torque. And non-contaminated condition of the implant abutment screw can significantly prevent reduction of the reverse torque compared to the primary torque.