Influence of repeated tightening and loosening of the prosthetic screw in micromovements abutment / implant.

Abstract

Background: Micromovements in the implant-abutment connection may influence periimplant bone preservation, especially in the cervical region of the implant. The purpose of this study was to evaluate and quantify these micromovements after repeated cycles of tightening and loosening the prosthetic screw using the method of three dimensional image correlation (DIC 3D). Materials and Methods: 10 Mis® Seven internal hexagon 4.2x13 implants were included in an acrylic block with similar elasticity of bone and randomly allocated into 2 groups. Mis® Titanium abutments (Standard cementing post, anti-rotational) were screwed to the implants at 30Ncm torque and loaded up to 200N with an universal testing machine (AG-I Shimadzu®) at a 30º angle. Samples were then randomly allocated into two groups. Group I was submitted to one cycle of loosening and retightening of the abutment screw and group II was submitted to 2 consecutive cycles of loosening and tightening of the abutment screw. Each sample was loaded again and the micromovements captured with Vic-3D (Correlated Solutions, Inc), in three axis U, V, W, corresponding to the movements in the mesio-distal, vertical and antero-posterior directions, statistical analysis was performed using SPSS 20.0, considering independent samples t-test for group comparison and paired samples t-test for intra-group comparison. Mixed ANOVA was used to determine the interaction of screw loosening and tightening cycles and load on the micromovements of the abutments. Results: No statistically significant differences were found between groups regarding the three directions, under any load. Also, no statistically significant differences were found between micromovements before and after the screwing cycles for each group. However, absolute displacement was higher in Group II under 100N load than in Group I after the protocol with a statistically significant difference of -0.168 (95% CI, -0.321 to -0.016), t(8)=-2.55, p=0.03. Conclusion: The implant/abutment connection according to the protocol performed, demonstrated good resistance and a precise fit between these interfaces, therefore, in case of unscrewing is not justified changing the screw.