In vitro analysis of orthodontic measurements on 3D-printed casts

Objective: One of the fundamental principles of orthodontic diagnostics is the measurement of study models. The aim of the study was to assess the suitability of 3D-printed models for metric orthodontic model analysis. Material and method: Ten Alignat impressions were taken from a Frasaco model (upper and lower jaw in habitual occlusion) and ten gypsum models made of plaster. The Frasaco model was also digitised with a 3D model scanner with a resolution of 10 μm (S600 Arti, Zirkonzahn GmbH, Gais, It). The digital model was reconstructed in OnyxCeph 3D Lab (ImageInstruments GmbH, Chemnitz) and exported for 3D printing. Ten model pairs were printed with a DLP (digital light processing) printer (SHERAeco Print D30 with SHERA model fast, Material-Technologie GmbH & Co. KG, Lemförde, Germany) and an FDM (Fused Depostion Molding) printer (Geeetech i3 Prusa, Getech Co. Ltd., ShenZen, PRC) with polylactide. The Frasaco model was measured ten times and all the other models once with a digital caliper (PeWe Tools Ltd, Trochtelfingen); the data were directly imported via USB interface. The key figures such as overbite, overjet, arch width, SI, si, Tonn, and the Bolton relations were determined. Results: For the measurement of the Frasaco model, 0.05% confidence intervals of ± 0.05-0.1mm and a mean standard deviation of 0.12mm were obtained. In the statistical analysis of the measured values by means of ANOVA with paired Mann-Whitney tests, only significant differences were found in the si, with 0.3 mm magnification for FDM models and a deviation of 0.4 mm reduced overbite in gypsum models and FDM models compared to the original. Conclusions: The measurement of study models with a digital caliper has an extraordinarily high degree of accuracy. Both the printed models, independent of the printing process and thus the virtual model, showed only minor deviations from the original in the examination. Virtual models, printed models, and gypsum models can be regarded as equivalent for orthodontic diagnostics. Keywords: 3D printing, orthodontics, CAD/CAM