Abstract
When mandibular incisors have erupted fully, there are two conditions of their alinement. The one is the group whose teeth aline regularly (Normal group), the other one is the group whose teeth crowd (Crowding group). The purpose of this study is to find what causes the difference between the two.
Materials consisted of study series of casts taken from 29 children, whose oral conditions in the deciduous stage were acceptable, and moreover, in whose growing process, situations such as premature loss, improper habit, and so on, which directly dominate tooth alinement or development of occlusion, were not found. On the average, children were observed ranged from 5 years of age to 8 years and 9 months of age, and the interval of this observation was 3 years and 6 months.
After the subjects was separated into 2 groups, diffe r ences between the two were investigated with respect to the tooth form, the arch form in the deciduous stage, and the changing process of dental arch. Moreover, how these differences take part in the alinement of mandibular permanent incisors was investigated by the factor analysis method.
