Cyclic loading impact on screw loosening of internally connected implants: an experimental study

Abstract

Objective The aim of this study was to assess impact of cyclic loading on screws attached to four different abutments to internally connected implants. Materials and methods Four groups (seven implants each) of dissimilar abutments were included in this study. Abutments were connected to Straumann tissue-level implants. Each implant was rigidly secured in a stainless steel cylindrical jig. A torque controller was used to tighten the abutments at 35 N cm. A 150 N cyclic load for 1 million cycles was applied to the implant at a 30° angle to the long axis to the implants. Periotest values (PTVs) were measured before and after cyclic loading and a digital torque gauge used to detect the removal torque values (RTVs) of abutments. The data were analyzed statistically using SPSS and Kruskal–Wallis tests and one-way analysis of variance were used to compare RTVs and PTVs after application of equal loads for each group. The Spearman correlation coefficient was applied to compare RTVs and PTVs after loading. Results The Straumann solid abutment and the Southern solid abutment showed no mechanical failures. Screws fracture was noted in nearly 85% of Implant Direct abutment, and 55% of the Blue Sky Bio abutments. The final mean PTV of the Blue Sky Bio abutments, the Southern Implants, and Implant Direct straight abutment was considerably higher than the final mean PTVs of Straumann solid abutment. Conclusion Abutments from the different manufacturers have different physical and chemical characteristics. So there was a potential risk of mechanical failure when the interchangeable abutments are used. Thus, the use of an abutment manufactured by the same implant company is highly recommended for the avoidance of loosening of the abutment screws.