Errors in guided dental implant placement on inclined surfaces with fully-guided systems

This study examines the impact of residual bone inclination on the accuracy of implant placement. In this in vitro study, ten replica models with inclined surfaces were fabricated using three-dimensional (3D) modelling software to assess implant placement accuracy on varying inclinations (90°, 15°, 30°, 45°, 60°). Implants were placed using two drilling protocols: a standard sequence (Group A) and a sequence beginning with a pointed drill to prevent slippage (Group B). Drill slippage and binding were recorded, and placement accuracy was measured by superimposing pre- and post-placement scans to calculate 3D positional errors. In total, 50 implants were placed across ten blocks, categorised by drill type (Group A: without sharp twist drill; Group B: with sharp twist drill) and angle (90°, 15°, 30°, 45°, 60°). Drill binding occurred more frequently at smaller angles, especially at 15° (100% in Group A; 80% in Group B). The Jonckheere-Terpstra test confirmed a significant trend of increased binding with smaller angles (p = 0.001 for Group A; p = 0.028 for Group B). The largest x-axis deviations occurred at 15°, with errors primarily to the left, which reflected expected slippage on inclined surfaces in both groups. While significant differences in anteroposterior (y-axis) and vertical (z-axis) deviations were observed at certain angles between Group A and Group B, the overall placement accuracy between the groups remained comparable. This study highlights the challenges of guided implant placement on inclined surfaces, where decreased drill angles lead to significant x-axis deviations.