Three-dimensional dental arch curvature in human adolescents and adults

The three-dimensional arrangement of dental cusps and incisal edges in huma n dentitions has been reported to fit the surface of a sphere (the curve of Monson), with a radius of about 4 inches in adults. The objective of the c urrent study was to compare the three-dimensional curvature of the mandibul ar dental arch in healthy permanent dentitions of young adults and adolesce nts. The mandibular casts of 50 adults (aged 19 to 22 years) and 20 adolesc ents (aged 12 to 14 years) with highly selected sound dentitions that were free from temporomandibular joint problems were obtained. The three coordin ates of cusp tips excluding the third molars were digitized with a three-di mensional digitizer, and used to derive a spherical model of the curvature of the occlusal surfaces. From the best interpolating sphere, the radii of the left and right curves of Spee (quasi-sagittal plane) and of molar curve of Wilson (frontal plane) were computed. Mandibular arch size (interdental distances) was also calculated. The occlusal curvature of the mandibular a rch was not significantly influenced by sex, although a significant effect of age was found (Student t, P < .005), The radii of the overall sphere, ri ght and left curves of Spee, and curve of Wilson in the molar area were abo ut 101 mm in adults, and about 80 mm in adolescents. Arch size was not infl uenced by either sex or age. The different curvatures of the occlusal plane in adolescents and adults may be explained by a progressive rotation of th e major axis of the teeth moving the occlusal plane toward a more buccal po sition. These dental movements should be performed in a frontal plane on an anteroposterior axis located next to the dental crown.