Effect of Implant Angulation on Long-Term Outcomes of Screw-Retained Versus Cement-Retained Single Implant Crowns: A Retrospective Cohort Study

Introduction: Implant angulation and prosthetic retention are critical determinants of the long-term success of implant-supported restorations. However, there is limited evidence to evaluate the combined influence on prosthetic survival and complication rates. This study aimed to assess the effects of implant angulation on the outcomes of screw-retained and cement-retained implant-supported crowns. Materials and methods: This retrospective cohort study was conducted using institutional electronic dental records. A total of 720 implant-supported single crowns with a minimum follow-up of five years were included. Cases were categorized based on the prosthetic retention type and stratified into angulation groups of 0-10°, 11-20°, and greater than 20°. Data on prosthetic survival, mechanical complications, and biological complications were also collected. Statistical analyses included independent samples t-test, chi-square test, Kaplan-Meier survival analysis, Cox proportional hazards regression, and receiver operating characteristic curve analysis. Results: The mean age of participants was 52.4 ± 11.6 years. No significant differences were observed in baseline characteristics between the groups (p > 0.05). Prosthetic survival decreased with increasing angulation. The five‑year cumulative survival rates for screw‑retained crowns were 98.2% (0-10°), 94.5% (11-20°), and 88.7% (>20°); for cement‑retained crowns, survival rates were 96.8% (0-10°), 87.3% (11-20°), and 72.4% (>20°). Screw‑retained restorations demonstrated significantly better survival across all angulation categories (log‑rank p < 0.001). At angulations greater than 20°, cement-retained restorations showed higher rates of mechanical complications, including crown decementation and screw loosening, compared to screw-retained restorations (p < 0.001). Biological complications such as peri-implantitis were also higher in cement-retained restorations (p < 0.001). Regression analysis identified cement-retained restorations (hazard ratio, 1.42) and angulation greater than 20° (hazard ratio, 1.87) as significant predictors of complications. Conclusion: Implant angulation had a significant impact on prosthetic outcomes, with higher angulations being associated with increased complication rates. Screw-retained restorations demonstrated a more favorable performance than cement-retained restorations, particularly at angulations greater than 20°. These findings highlight the importance of considering the implant angulation during treatment planning. A preference for screw-retained designs in highly angulated cases may improve long-term clinical success.