Influence of Antimicrobial Sealing Gels on Reverse Torque Values of Implant–Abutment Screws Following Thermomechanical Loading: A Comparative In Vitro Study

Background: Abutment screw joint stability is essential for the long-term success of implant-supported restorations. However, the effects of antimicrobial agents on implant–abutment screw mechanics remain unclear. This in vitro study evaluated the effects of chlorhexidine and silicone-based sealing gels on reverse torque values (RTVs) following thermomechanical loading. Methods: Forty-five Straumann implant analog–abutment assemblies were allocated to three groups (n = 15 per group): untreated control, 2% chlorhexidine gel, and a silicone-based gel (Flow.sil) applied to the abutment screw threads prior to tightening. Cemented standardized monolithic zirconia crowns were subjected to thermomechanical aging (750,000 cycles, 100 N, 2 Hz, 5–55 °C). The mechanical performance of the screw joint was assessed using RTVs, whereas calculated torque loss percentages were reported as a complementary outcome to facilitate the clinical interpretation of the reverse torque findings. Data were analyzed using Shapiro–Wilk and Levene’s tests, one-way analysis of variance (ANOVA), and Tukey’s HSD test (α = 0.05). Results: Significant differences among groups were observed for post-aging RTVs (p < 0.001). The control group exhibited the highest RTVs (33.03 ± 6.57 Ncm), suggesting the most favorable post-aging reverse torque performance. RTVs were lower in the chlorhexidine (25.29 ± 4.78 Ncm) and Flow.sil (23.16 ± 7.39 Ncm) groups. Although the sealing agents did not differ significantly, chlorhexidine yielded numerically higher RTVs than Flow.sil. Conclusions: Under the present experimental conditions, direct application of antimicrobial and silicone-based sealing agents to the abutment screw threads was associated with lower RTVs than the untreated control condition. Accordingly, the potential mechanical effects of these materials should be considered when selecting screw-sealing protocols.