Technical Complications and Marginal Bone Loss Depending on the Crown Material of Dental Implants in the Posterior Region: A 3-Year Randomized Clinical Study

<b>Background/Objectives:</b> This single-center, randomized controlled clinical trial evaluated the impact of two crown materials-lithium disilicate (LS2) and a polymer-infiltrated hybrid ceramic (HC)-on the marginal bone loss (MBL) and the technical complications in implant-supported single-tooth restorations over a three-year period. <b>Methods:</b> Sixty patients with posterior single-tooth gaps were randomly assigned to receive either LS2 or HC crowns on iSy (Camlog) implants. All of the restorations were fabricated as CAD/CAM-based hybrid abutment crowns bonded to prefabricated titanium bases. Standardized radiographs were taken at the baseline (T0) and at three years (T1) to assess the MBL using ImageJ software. The technical complications were prospectively recorded. The data analysis was descriptive and exploratory. <b>Results:</b> Fifty-eight cases were available for the final evaluation. The three-year implant survival rate was 100%. The mean marginal bone remodeling was minimal (mesial: LS2 0.15 mm, HC 0.08 mm; distal: LS2 0.13 mm, HC 0.12 mm), with no statistically significant intergroup differences. Bone apposition was observed in 74.1% of the cases. The male patients showed a significantly greater mesial bone loss (<i>p</i> = 0.024). Technical complications occurred more frequently in the HC group, including crown fractures (25%), decementation (17.9%), and screw loosening (14.3%). In the LS2 group, only screw loosening (12.5%) was observed. <b>Conclusions:</b> The lithium disilicate-based hybrid abutment crowns demonstrated a high clinical reliability with stable peri-implant bone and fewer technical complications over three years. In contrast, the hybrid ceramic crowns were associated with a higher rate of mechanical failure. Material selection should therefore be a key consideration in planning implant-supported single-tooth restorations.