Operator Experience and Scanning Strategy Affect the Trueness of Full-Arch Intraoral Scans: An In Vitro Study Comparing Dental Students and Practicing Dentists

Objectives To evaluate the influence of operator experience (dental students vs. practicing dentists) and scanning strategy (linear, zig-zag, combined) on the trueness of full-arch intraoral scans, and to assess their interaction. Materials and Methods In this in vitro study, 20 dental students and 20 practicing dentists each acquired three full-arch scans (120 scans total) of a standardized reference model (an onlay preparation at tooth 16, an inlay preparation at tooth 14, and full-crown preparations at teeth 21 and 26) with an intraoral scanner (TRIOS 6, 3Shape), applying a linear, a zig-zag, and a combined scanning strategy. Each scan was superimposed on an industrial laboratory reference scan using principal component analysis for coarse alignment and a trimmed point-to-plane iterative closest point (ICP) algorithm for fine registration. Point-to-surface deviations were calculated for 149,472 area-weighted sample points per scan. Outcome measures included mean absolute deviation, root-mean-square (RMS) deviation, and the percentage of scanned area within ±50 μm and ±100 μm of the reference. Group differences were analyzed with the Mann-Whitney U test (plus Welch’s t-test and Cohen’s d), and strategy differences with the Friedman test and Holm-corrected post hoc Wilcoxon signed-rank tests (α = 0.05). Results Across all 120 scans, the mean absolute deviation was 75.3 μm (RMS 127.5 μm); 58.5% of the scanned area fell within ±50 μm and 78.7% within ±100 μm of the reference. Practicing dentists achieved significantly higher trueness (65.4 ± 14.0 μm) than dental students (85.2 ± 17.9 μm; Mann-Whitney U = 324.0, p < 0.001; Welch t = 3.89, p < 0.001; Cohen’s d = 1.23). Scanning strategy also had a significant overall effect (Friedman χ 2 = 6.20, p = 0.045): the linear strategy (68.6 μm) was significantly more accurate than the combined strategy (78.1 μm; Holm-corrected p = 0.047); linear vs. zig-zag (79.1 μm; p = 0.106) and zig-zag vs. combined (p = 0.889) were not significantly different. The magnitude of the group difference varied by strategy, from 12.1 μm for the linear strategy (p = 0.066) to 31.3 μm for the zig-zag strategy (p < 0.001). Conclusions Operator experience was the dominant factor influencing intraoral scanning trueness in this in vitro model, with a large effect size. Scanning strategy had an independent, smaller but significant effect, with the linear strategy yielding the highest trueness overall and narrowing the gap between less and more experienced operators. These findings support structured training in a standardized, linear scanning strategy, particularly for less experienced operators.