Evaluation of different tightening protocols on angled screw channel abutments after cyclic loading: An in vitro study

Statement of problem: Screw loosening remains one of the most common complications associated with implant-supported restorations. The available literature is scarce regarding the most efficient method of tightening definitive abutment screws for angled screw channel (ASC) abutments. Purpose: The purpose of this in vitro study was to identify the optimal screw tightening protocol for ASC abutments by evaluating the influence of different protocols on reverse tightening values (RTVs). Material and methods: Fifty implants were randomly assigned to 5 groups (n=10). Implants were mounted and received a cover screw and impression coping to simulate the clinical scenario. Each group was allocated to one of the following protocols: tightened once (1×), tightened twice (2×), tightened twice at a 10-minute interval (2× [10 min]), tightened, countertightened, then tightened again (TCT) and tightened, countertightened, tightened, countertightened, then tightened (TCTCT). A monolithic zirconia central incisor implant crown was fabricated by using computer-aided design and computer-aided manufacturing (CAD-CAM) and cemented onto the ASC abutment. The crown-abutment assemblies were secured onto the implants with the Gold-Tite abutment screw by using their assigned tightening protocols. Each screw was tightened to the recommended value of 20 Ncm with a calibrated digital torque measuring device. Specimens were subjected to 250 000 cycles of cyclic loading simulating 3 months of function with a universal testing machine. RTV was measured for each specimen. Results: The mean RTV for all the groups ranged from 13.5 Ncm to 15.9 Ncm. The highest mean RTV was found with the (1×) protocol. However, the difference was not statistically significant among any of the groups (P>.05). Conclusions: Multiple retightening and time intervals between tightening events of these ASC abutment screws did not have a significant influence on RTV under simulated function of 3 months. The one time (1×) tightening protocol can be recommended as a suitable method for ASC abutments, thus avoiding unnecessary retightening.