The relationship between time of re-tightening and preload loss of abutment screws for two different implant designs: an in-vitro study.

Abstract

The loosening of an abutment screw is one of the most frequent complications in implant-prosthetic rehabilitation, especially for single crown cemented prostheses. This complication is due to several mechanical factors, including: type of connection, abutment-screw geometry, settling effects, and cyclical load. The purpose of the present in-vitro study was to compare and associate different times of re-tightening with reductions in preload losses. We evaluated 40 internal hexagon dental implants and 40 external hexagon dental implants, with their related abutment screws. The implants were embedded in acrylic resin in cylindrical polyvinyl chloride tubes (diameter, 26 mm; height, 20 mm). The abutments were fixed to the implants with screws to an initial torque of 35 Ncm using a digital torque meter with decimal precision. The two different types of connection were randomly divided in four subgroups of 10 samples each. One subgroup was used as control. The test groups underwent re-tightening to the same initial torque at increasing times from initial torque application for tightening of the abutment screws, to their re-tightening at 2 min, 5 min, and 10 min. The re-tightening time of 2 min shows significantly reduced preload loss. Randomized clinical trials are strongly required to provide clinicians with a beneficial standardized protocol of re-tightening that can be applied in routine clinical practice.