Comparing 3-D Scanning Methods in Generating Digital Diagnostic Models

Objectives: To assess the accuracy of two methods of generating a digital 3-D orthodontic study model either by scanning a positive representation of dental anatomy or by scanning a negative representation of dental anatomy in relation to the plaster model of the same patients.
Methods: Following IRB approval and reliability testing, polyvinyl siloxane impressions of the maxillary and mandibular arches of 16 subjects selected from Indiana University School of Dentistry. Impressions were taken and immediately scanned using the Ortho Insight 3D scanner (Motionview software) to avoid any dimensional change. Impressions were poured with orthodontic plaster within 24 hrs to create the conventional study models. Each stone model was then scanned using the same scanner to generate digital models. The same set of parameters was measured on the two types of digital models using Motionview software and on the stone model using a boley-gage caliper. Linear mixed effects models were used to compare the measurements among the gold standard, digital impression, and digital cast. In addition, intraclass correlation coefficients (ICCs) and Bland-Altman plots were calculated to evaluate reliability and the agreement of the two digital methods with the gold standard. Statistically significant differences were determined at p ≤ 0.05.
Results: No statistically significant differences were found between the positive and negative digital methods, however nine measurements (Intermolar, Inter-second premolar, and Inter-first premolar arch widths; anterior right and posterior right arch lengths; Tooth 3, 19, and 25 widths; Tooth 3 length) were significantly different comparing either the positive (stone model) digital models and the negative (dental impression) digital models to the plaster models.
Conclusions: There is no statistically significant difference between the two methods of generating 3-D digital orthodontic study models. The results provide evidence that the process of fabricating stone models from dental impressions can potentially be bypassed when cataloguing digital models in a clinical setting.