Mechanism of and factors associated with the loosening of the implant abutment screw: A review

Objective While the loosening of the abutment screw is one of the most common complications in implant-supported restorations, there is a lack of comprehensive literatures for mechanism of and factors associated with the loosening of the implant abutment screw. The review was to summarize the mechanism of and factors associated with the loosening of the implant abutment screw. Overview A total of 99 relevant articles were included in the literature review. The mechanism of the abutment screw loosening was explained. The factors contributed to abutment screw loosening were divided into five aspects and then expounded respectively. Conclusions The internal connection and abutments with anti-rotational and conical designs have better resistance to screw loosening. Cantilevers increase the risk of screw loosening. The effect of surface treatment of the abutment screw is unsure. Clinicians need to tighten the abutment screw to the recommended torque while avoiding repeated tightening and loosening, and increase the frequency of follow-ups to retighten the loosened screws in time. Clinical Significance While the loosening of the abutment screw is one of the most common complications in implant-supported restorations, there is a lack of comprehensive literatures for mechanism of and factors associated with the loosening of the implant abutment screw. The review was to summarize the mechanism of and factors associated with the loosening of the implant abutment screw, so that clinicians may make better choices in clinical practice.