Making three-dimensional Monson's sphere using virtual dental models

Abstract

The Monsons sphere and curve of Wilson can be used as reference for prosthetic reconstructions or orthodontic treatments. This study aimed to generate and measure the three-dimensional (3-D) Monsons sphere and curve of Wilson using virtual dental models and custom software. Mandibular dental casts from 68 young adults of Korean descent were scanned and rendered as virtual dental models using a 3-D digitizing scanner. 26 landmarks were digitized on the virtual dental models using a custom made software program. The Monsons sphere was estimated by fitting a sphere to the cusp tips using a least-squares method. Two curves of Wilson were generated by finding the intersecting circle between the Monsons sphere and two vertical planes orthogonal to a virtual occlusal plane. Non-parametric Mann-Whitney and Kruskal-Wallis tests were performed to test for difference between sex and in cusp number within tooth position. The mean radius of Monsons sphere was 110.89 ± 25.75 mm. There were significant differences between males and females in all measurements taken (p < 0.01), within 16.87 - 17.27 mm. Furthermore, morphological variation derived from variability in cusp number in the second premolar and second molar were not found to influence occlusal curvature (p > 0.05). This study describes a best-fit algorithm for generating 3-D Monson's sphere using occlusal curves quantified from virtual dental models. The radius of Monson's sphere in Korean subjects was greater than the original four-inch value suggested by Monson. The Monsons sphere and curve of Wilson can be used as a reference for prosthetic reconstruction and orthodontic treatment. The data found in this study may be applied to improve dental treatment results.