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Angled Channel Abutment Screw Reverse Torque Values Following Mechanical Cycling


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Introduction: Screw-retained implant restorations employ an angled screw channel (ASC) to allow access from a more favorable, and/or esthetic location. Retention screw insertion torque is applied at an angle greater than 0. Theoretically, this should diminish the amount of realized screw torque due to the angle of force application. Objective: To compare reverse torque values (RTV) of abutment screws tightened to manufacturers recommended value from 3 different angles (0, 10, and 20) following off-angled, cyclic load testing. Methods: Thirty-one implant abutments/screws (MIST IC S-Link)and implants (BIOMET 3i 4.1mm Osseotite external hex) were divided into 3 angulation groups (0, 10, and 20) with sample sizes of 11, 10, and 10 respectively. Customized3D printed mounts for a chewing simulator (SD Mechatronik, Feldkirchen-Westerham)were fabricated in ABS plastic and designed to hold the implant long axis at 50 to the applied load. Samples were assembled, secured into custom mounts, and prepared for testing in a random order. Angulation guides (0, 10, and 20) were used to direct a20Ncm insertion torque to abutment screws using an adjustable torque wrench (Zimmer Biomet) and appropriate hexalobular driver. Torque was reapplied 10 minutes after initial application. A cyclic load (50N, 250,000X) was applied (3mm dia cobalt chrome ball) to lingual of the abutments. Immediately following testing, the digital torque gauge was used to measure RTV at 0 to the long axis of all samples. RTVs were compared using analysis of variance (ANOVA) alpha=0.05. Results: ANOVA found no significant difference in post-cyclical mean RTVs values (13.5Ncm/0, 12.6Ncm/10 and13.2Ncm/20) between angulation groups (p=0.31). All post-cycle mean RTVs were less when compared to the applied initial torque (20Ncm). Conclusion: This randomized invitro study found abutment screw driver insertion angle did not significantly influence mean screw RTVs between groups.



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