Accuracy and reproducibility of linear measurements of resin, plaster, digital and printed study-models

Objectives: To compare the accuracy and reproducibility of measurements of on-screen three-dimensional (3D) digital surface models captured by a 3Shape R700™ laser-scanner, with measurements made using a digital caliper on acrylic, plaster models or model replicas. Subjects and Method: Four sets of typodont models were used. Acrylic models, alginate impressions, plaster models and physical replicas were measured. The 3Shape R700™ laser-scanning device with 3Shape™ software was used for scans and measurements. Linear measurements were recorded for selected landmarks, on each of the physical models and on the 3D digital surface models on ten separate occasions by a single examiner. Results: Comparing measurements taken on the physical models the mean difference of the measurements was 0.32mm (SD 0.15 mm). For the different methods (physical versus digital) the mean difference was 0.112mm (SD 0.15 mm). None of the values showed a statistically significant difference (p < 0.05) on the Objet Eden 250™ 3D prints, alginate impressions, plaster and acrylic models. Conclusion: The comparison of measurements on the physical models showed no significant difference. The 3Shape R700™is a reliable device for capturing surface details of models in a digital format. When comparing measurements taken manually and digitally there was no statistically significant difference. The Objet Eden 250™ 3D prints proved to be as accurate as the original acrylic, plaster, or alginate impressions as was shown by the accuracy of the measurements taken. This confirms that using virtual study models can be a reliable method, replacing traditional plaster models.