Dental maturity is one of the index of physiological maturity indicators. To investigate the relationship between dental maturity and chronological age, the author took the orthopantomograms of 984 students, aged 7 through 17 years, having normal occlusion. The orthopantomograms were examined and calcification degree of each tooth on the left side was rated according to the method described by Demirjian. On the basis of findings of this study, the following results were obtained. 1. The root completion periods of mandibular permanent teeth were as follows; Central Incisor M 8.32 ± 1.03years F 7.96 ± 1.04 years Lateral Incisor M 9.40 ± 1.30years F 9.01 ± 0.90years Canine M 12.81 ± 1.24 years F 11.42 ± 0.94 years 1st Premolar M 12.76 ± 1.74years F 12.19 ± 1.33years 2nd Premolar M 13.31 ± 1.88 years F 12.88 ± 1.49 years 1st Molar M 9.60 ± 1.69 years F 9.30 ± 1.16 years 2nd Molar M 14.38 ± 1.73 years F 13.96 ± 1.63 years 2. Sexual differences in same age group at given calcification stage were not significant statistically. 3. The developmental order in mandibular permanent teeth was as follows; a) central incisor, b) lateral incisor, c) 1st molar, d) canine and 1st premolar, e) 2nd premolar, f) 2nd molar.