Reliability and validity of measurements on digital study models and plaster models

Objective: To compare manual plaster cast and digitized model analysis for accuracy and efficiency. Material and methods: Nineteen plaster models of orthodontic patients in permanent dentition were analyzed by two calibrated examiners. Analyses were performed with a diagnostic calliper and computer-assisted analysis after digitization of the plaster models. The reliability and efficiency of different examiners and methods were compared statistically using a mixed model. Results: Statistically significant differences were found for comparisons of all 28 teeth (P < 0.001), mandibular intermolar width (IMW, P = 0.0453), and overjet (P < 0.001 to P = 0.0329). Single-tooth measurements tended to have larger values when measured manually and the SD was between 0.06 and 1.33 mm. Digital analyses gave significantly higher values for mandibular IMW and overjet. Less time was needed for digital measurements. Conclusion: Clinical significance of the differences between the methods compared did not appear significant. 3D laser-scanned plaster model analysis appears to be an adequate, reliable, and time saving alternative to analogue model analysis using a calliper.