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The previous researches on racial differences in the crown trait and the dental arch morphology have often treated these two factors independently. The purpose of this study was to investigate, recognizing their racial differences, whether there are any association between them.The sample consisted of plaster casts of dentition obtained from 142 Japanese, 109 Cancasian and 121 inhabitants of the Andes in Peru. The casts were preserved at the Department of Orthodontics of Tokyo Medical and Dental University.The variations of 30 crown traits, categorized and quantitatively graded, were compared among three races using two methods. Chi-square test analyzed the frequency distribution of each crown trait. The other method analyzed the total variation of 30 crown traits in each sample by the computation of the parameter of similarity.On the other hand, an interracial comparison of the dental arch morphology was made by superimposing the occlusal outlines of all teeth, each of which had been numerically expressed by polar coordinates of 36 points plotted equi-angulary on the occlusal contour.The results were as follows:1. Trait frequencies of shovel-shape, interstitial tubercle, groove pattern of the Y type and Carabelli's cusp were significantly different among the races examined, and the shovel-shape appeared to be a hereditary characteristic.2. The dental arch morphology, especially in the anterior part, was different among the races.3. The crown trait, particulary the shovel-shape, was related to factors composing the anterior part of upper dental arch; namely, the arch length, arch width and winging of the central incisors.

Dental anthropological study on crown trait.