On the augmented reproducibility in measurements on 3D orthodontic digital dental models and the definition of feature points

Abstract

Abstract Objective: The objective of this study was to explore digital measurement methodology on 3-dimensional (3D) dental models. Standardised manipulation and practices have lead to reliable measurements on plaster casts. Identifying landmarks on digital models or digitised plaster casts is fundamentally different from actual measurements. Three-dimensional models are represented on flat screens and landmarks are individually indentified. A procedure is proposed that resolves the deficiencies associated with a 2-dimensional (2D) display through an appropriate model representation and through local optimisation. Methods: Fifteen models (OrthoProof) were exported to a locally developed 3D point indication software package, in which two measurement approaches were implemented involving standard projection with and without local search. Nine linear measurements were obtained from plaster casts and digital models. Statistical analysis included correlation and Friedman’s non-parametric analysis of variance (ANOVA). Results: For five out of nine linear measurements, digital indications yielded results significantly different from manual measurements (p = 0.05). Local search considerably improved measurement accuracy and reliability. Conclusions: Measurements on plaster casts can differ significantly from those obtained through digital identification methods. These differences prove to be clinically relevant. Standardisation and optimisation resulted in improved and extremely reliable digital measurements.