Evaluation of Dimensional Deviations Across a Digital-to-Physical Workflow for Orthodontic Appliance Fabrication Using CAD Surface Inspection

Digital-to-physical orthodontic workflows combine intraoral scanning, 3D printing, rescanning and thermoforming, but each step may introduce dimensional deviation affecting final appliance geometry. This pilot methodological study evaluated relative dimensional deviations across selected stages of a biomedical manufacturing workflow for orthodontic appliances. Anonymized intraoral scan datasets from two patients with eugnathic occlusion were used, providing four arch-level datasets. CAD inspection compared IOS data, printed models, powder-coated printed models, and thermoformed appliances, with an analysis of global RMS surface deviation, anterior/posterior regional differences, spray-related surface offset and material-thickness effects. The highest mean global RMS deviation was found for IOS vs. a printed model (0.090 mm), followed by IOS vs. a powder-coated model (0.088 mm), whereas the direct printed model vs. powder-coated model comparison showed a lower mean RMS deviation of 0.039 mm. Regional analysis showed higher RMS deviations posteriorly (0.077 mm) than anteriorly (0.047 mm). Thermoformed appliance adaptation was affected by material thickness, with a mean RMS deviation of 0.207 mm for 1.0 mm material and 0.282 mm for 1.5 mm material. Local incisor analysis estimated the spray-related surface offset at approximately 0.030 mm. The main dimensional discrepancy was associated with printed model fabrication, while posterior regions and thicker thermoformed material showed greater deviation.