3D Modeling and Visualization of Orthodontic Tooth Movement

Objectives: The study aims to (i) test the accuracy and precision of a newly developed computer-based method of superimposition of three-dimensional (3D) images of dental casts onto two-dimensional (2D) images of lateral cephalograms, and (ii) determine the relationship between resultant orthodontic tooth movement and pre-treatment parameters of overjet, extraction pattern, age, crowding, and the antero-posterior and vertical skeletal relationships. Methods: (i) Nine steel ball bearings (0.99 mm in diameter) were glued onto a dry skull and the inter-ball bearing distances were measured using a digital caliper (Mitutoyo, Japan). A lateral cephalogram of the same dry skull and a dental cast were taken and digitized. The virtual 3D cast was superimposed onto the virtual cephalogram and the inter-ball bearing distances were measured off the computer. (ii) Pre- and post-treatment lateral cephalograms and dental casts of 39 subjects with Class II Division 1 malocclusions were digitized and superimposed. Antero-posterior, vertical and transverse molar and incisor movements were measured with the software Rapidform2004™ (Inus Technology, Seoul, Korea). Results: (i) Bland-Altman analysis showed that there is no significant difference between computer-based measurements and those made with the digital caliper. (ii) Using linear regression analysis, with a significance level at 5%, increasing age was found to be related to decreasing mesial molar movement(p=0.012). Increasing crowding was significantly related to increasing incisal movement in the antero-posterior plane(p=0.033). More incisor extrusion was observed in subjects with all four first premolars extracted compared to those with maxillary first premolar and mandibular second premolar extractions (p=0.003). Conclusion: The computer-based method of superimposing the 3D image of the dental cast onto the 2D image of the lateral cephalogram is accurate and precise. Age, crowding and extraction pattern have been shown to affect the amount of incisor and molar movements in the correction of Class II Division 1 malocclusions.