KHẢO SÁT LỰC MÔ-MEN XOẮN TRƯỚC VÀ SAU TẢI LỰC TRONG PHỤC HÌNH ALL-ON-FOUR HÀM DƯỚI

Abstract

Objective: To evaluate the percentage of torque loss in prosthetic screws connected to multi-unit abutments (MUAs) with different angulations (0°, 17°, and 30°) before and after mechanical loading in mandibular All-on-Four prostheses. Materials and Methods: This in vitro study was conducted on three edentulous mandibular acrylic models simulating D2–D3 bone density. Each model received four Osstem TSIII implants: two anterior implants restored with 0° MUAs and two posterior implants with MUAs angulated at 0°, 17°, or 30°, depending on the study group. Full-arch prostheses were designed using Exocad software, milled from PMMA via CAD/CAM technology, and secured with prosthetic screws torqued to 20 Ncm. Detorque values were recorded before and after cyclic loading. Data were analyzed using JASP version 0.17.2.1. Results: Torque values decreased significantly after loading across all groups. The mean post-loading torque loss (%Rp) increased with abutment angulation: 6.19% (0°), 9.68% (17°), and 16.1% (30°). A statistically significant difference in %Rp was observed between the 0° and 30° groups (p = 0.001), while differences between 0° vs. 17° and 17° vs. 30° were not statistically significant (p > 0.05). Similarly, the average torque loss (%R') also increased with angulation, showing a significant difference between 0° and 30° groups (p = 0.001). Conclusion: MUA angulation has a significant impact on post-loading torque loss. A 30° angled MUA increases the risk of prosthetic screw loosening in mandibular All-on-four restorations.