Screw Loosening and Torque Loss of Zirconia-Based Implant- Supported Dental Prostheses: A Retrospective Clinical Study.

PURPOSE: Dental implants are a widely used and effective method for tooth replacement, yet complications such as abutment screw loosening remain a challenge. The aim of this study was to investigate the effect of different abutments, connection types and restoration types on abutment screw loosening. MATERIALS AND METHODS: A retrospective analysis was conducted on 161 patients (85 women, 76 men; mean age 53 ± 6.3 years) with 308 abutments in zirconia-based implant-supported fixed dental prostheses (FDPs). Kaplan-Meier analysis and the log-rank test were used to analyze and compare the screw loosening probabilities and mean estimation time to torque loss after loading of implant supported restorations with different implant systems, abutments and restorations type, and tissue vs bone level implants. The torque value of studied abutments was analyzed by Kruskal-Wallis test and Mann-Whitney Test. One way analysis of variance and independent sample t test were used to compare torque loss value of abutment's type, single vs multiple FDPs, and tissue Vs bone level implants. The level of significance was set at 0.05. RESULTS: The overall survival rate of implant-supported FDPs was 99.2%. Complete loosening occurred in 2.1% of abutments. Torque loss values were significantly different between implant systems (p < 0.001), restoration types (p < 0.001), and tissue-level versus bone-level implants (p < 0.05). Tissue-level implants and multi-unit FDPs demonstrated more removal torque. No significant differences in torque loss were found between angled, straight, and solid abutments (p = 0.19). CONCLUSION: Torque loss and probability of screw loosening of different implant systems were significantly different. Multi-unit FDPs and bone level implants showed significantly less torque loss while abutment type did not influence the screw loosening.