Influence of posterior adjacent tooth presence, implant depth, and scanning strategies on trueness in partial edentulism

To evaluate the trueness of digital implant impressions in partially edentulous models according to posterior adjacent tooth presence, implant depth, and intraoral scanning strategy. Two maxillary models (Kennedy Class II Mod I) with implants at 1 mm (M1) and 3 mm (M3) subgingival depths were used. The left side retained the second molar, whereas the right side was edentulous. A confocal intraoral scanner was used with 4 strategies: right and left straight (RS, LS), and right and left zigzag (RZ, LZ). Each strategy was repeated 10 times ( n = 80). Laboratory scans served as reference. Trueness was evaluated by root mean square (RMS), linear deviation of scan bodies, and inter-implant distance. Data were analyzed using two-way ANOVA (α = 0.05). The presence of a posterior adjacent tooth resulted in lower deviations than its absence (This finding was obtained from the comparison of scanbody (SB) 16 and SB 26; statistically significant differences were observed for RMS in M1 RZ ( p < 0.001) and M1 LZ ( p = 0.002), and for linear deviation in M1 LZ ( p < 0.001), M3 LS ( p = 0.005), and M3 LZ ( p = 0.005)). Implants placed at 3 mm depth showed significantly higher deviations than those placed at 1 mm depth ( p < 0.05). Straight scanning strategies resulted in lower deviations than zigzag strategies ( p < 0.01). Posterior adjacent tooth presence, implant depth, and scanning strategy significantly influenced trueness. While straight scanning strategies maintained deviations within clinically acceptable limits, deep implants in edentulous terminal areas scanned with zigzag protocols exceeded the 100–150 μm linear threshold, representing the worst-case clinical scenario.