Effect of Tightening Protocol on Reverse Torque and Plastic Deformation of Dynamic and Conventional Titanium Abutment...

Preload loss and plastic deformation of titanium abutment screws under repeated tightening are clinically significant yet incompletely characterized across systems with differing head geometries and surface treatments. Two ISO 14801-certified titanium screws were evaluated: hexalobular-head gold-plated (Gold-Tite^®; 3i Zimmer Biomet, now ZIMVIE) and anodized star-shaped (Vega^®; Klockner^®). Six groups (n = 5 screws) varied by screw type, torque (20-40 N·cm), and cycle count (10 or 20). Reverse torque value (RTV) was recorded at every cycle and analyzed at the screw level; a linear mixed-effects model (screw as random effect) characterized how RTV evolved across cycles, with screw-level non-parametric tests for between-protocol contrasts. Micro-CT (19.9 μm; n = 3 per group) used Otsu segmentation. RTV was lower than insertion torque in every screw (30/30; 73-89% of applied torque). RTV declined significantly across cycles in the Vega/Klockner system (-0.17 N·cm per cycle, p = 0.006) but not in the ZFX/ZIMVIE system (p = 0.302), which showed greater between screw variability. Between protocol contrasts at n = 5 were null or underpowered. Micro-CT showed head localized change in both systems (mean cross-sectional area essentially unchanged); in the ZFX/ZIMVIE screws, this change appeared specifically under the over-use condition, whereas the Klockner screws showed comparable head change across all protocols. Preload loss is intrinsic to abutment screw tightening irrespective of design; RTV behaviour under repeated cycling is system-dependent, and abutment screws should be treated as limited-use components.