抄録
Measurements of the maxillary incisors were taken in four tribes (Han tribe, Man tribe, Hui tribe and Chaoxian tribe) living in Northeastern China. Regressive phenomena of the lateral incisors and comparison among four tribes were investigated. The results were as follows : 1. Both the central and lateral incisors were the largest in the Man tribe and the Hui tribe, but the smallest in the Chaoxian tribe. 2. The incidence rate of microdont in the lateral incisors was the highest in the Han tribe and the Chaoxian tribe, and microdont scarcely appeared in the Man tribe and the Hui tribe. 3. As compared with the central incisors, the reduction index of the lateral incisors showed low diminution rates in the labiolingual diameter among the four tribes. In the mesiodistal diameter, however, the diminution rates were extremely high and the Han tribe and the Chaoxian tribe showed higher reduction rates than the Man tribe and the Hui tribe. In the crown area, the Han tribe showed the highest diminution rate after the Chaoxian tribe. 4. On the basis of the incidence rates for the group with an extensive degree of definite regression of the lateral incisors and for the group with a slight degree of regression, determined by the reduction index, regression in the labiolingual diameter was slight in most cases. Of the four tribes, regression in the mesiodistal diameter was highest in female of the Chaoxian tribe, and was lowest in male of the Man tribe.
