Three-dimensional analysis of occlusal curvature in healthy Japanese young adults

Knowledge of the standard value of the occlusal curvature would be helpful when providing oral rehabilitation for patients with or without occlusal derangement. Dentists often use a 4-inch radii arc as the standard based on Monson spherical theory. However, the validity of application of this theory in Japanese has not yet been verified. The objective of this study was to determine the typical shape of the occlusal curvature in Japanese adults and investigate the relative contribution of each factor to the depth of the curvature, as the initial phase, to prove the validity of determination of occlusal curvature. Seventy-nine Japanese adults (42 males and 37 females, aged 18 to 37 years) with intact dental arches were recruited, and the occlusal curvature was estimated by calculating the radius and center position of the approximate sphere. Besides, the relative contribution of gender, age, dental arch length and width, overjet, overbite for the radii was calculated. The median radius of the sphere was 110.6 mm, larger than the 4-inch value advocated by Monson. This indicates the necessity to reconsider the application of the method of occlusal plane analysis in Japanese individuals. Median position of the centre was 64.6 mm anterior to and 68.5 mm above the mid-point between condyles. Relative contribution of overbite for the radii was 10.9%, the highest amongst the factors. Therefore, a typical shape of the occlusal curvature was observed in Japanese subjects. Overbite is considered as one of the principal factors correlated to the depth of the occlusal curvature.