Abstract: The materials investigated were 97 maxillary first permanent molars of South Chinese.
The authors have studied the relationship among the degree of tooth attrition, the tooth index and the age of 97 M1. A trinal regression formula with two variables, the degree of tooth attrition and the tooth index, was obtained. The values of the correlation coelfieient and the standard estimation error show that the trinal regression formula is better than the dual regression formula for estimating age.

Key words: Trinal regression; Estimating age; South Chinese