Monson's sphere in Chinese young adult females with individual normal occlusion: a preliminary study using digital models.

BACKGROUND: This study investigated the characteristics of Monson's sphere in Chinese young adult females with individual normal occlusion to provide a reference for oral rehabilitation in prosthodontic and orthodontic treatments. METHODS: Points at the dental cusps and incisal edges were selected from 51 digital mandibular dental models of Chinese young adult females (aged 18-22 years) with individual normal occlusion. Monson's spheres were fitted to the selected points based on the least-squares principle and the radii were calculated. The deviation of each selected point from its relative spherical surface was also calculated. The radii and deviations of these points were examined using conventional descriptive statistics and distributions of the most deviated points inside and outside the spheres were analyzed. RESULTS: The mean radius of Monson's sphere in Chinese young adult females was 79.60 +/- 14.13 mm. The deviation of each selected point from its relative sphere surface was 0.38 +/- 0.30 mm. The maximum deviations inside and outside the sphere were 0.93 +/- 0.25 mm and 0.95 +/- 0.30 mm, respectively. The most deviated points outside the spheres were mainly distributed at the distolingual cusps of the mandibular second permanent molars (31.37%), while those inside the spheres were mainly distributed at the mesiolingual cusps of the mandibular first permanent molars (45.10%). CONCLUSIONS: The radius of Monson's sphere in Chinese young adult females was smaller than the classic four-inch value suggested by Monson. Deviation was observed from all selected points to their Monson's sphere surface, with the most deviated points distributed primarily in the molar region.