A Study on the Classification of the Stage of Root Development and Crown Eruption for Permanent Teeth

영구치의 치근발육과 맹출시기의 분류에 관한 연구

This study was performed to investigate the age distribution with tooth calcification and degree of eruption of permanent teeth. For the study, healthy 184 patients from 5 to 19 years old without any previous serious dental treatment were randomly selected, and intraoral standard films and dental casts were taken for evaluation of stage of calcification and degree of eruption, respectively. Tooth calcification of 13 stages, designed by the author based on the Nolla's classification and eruption level of 4 or 5 degree was used. Data were processed by SAS/Stat program and the obtained results were as follows; 1. The age of root completed with open apex in lower posterior teeth were 13.8 years for first premolar, 14.0 years for second premolar, 10.5 years for first molar, and 14.2 years for second molar. There were no significant difference between right and left side. 2. As for the sequence of eruption, first molar was the first teeth erupted in upper arch, while central incisor was the first teeth in lower arch. In general, eruption of lower teeth were slightly earlier than the corresponding teeth of upper arch. 3. There were no difference of age of the same stage of development between Nolla's and the author's classification. From the results, the author's classification can be used for estimation of age with more finely in age of 8 to 15 years old. 4. Multiple regression equations for age with Nolla's(Ns) and the author's(Ks) classification of tooth calcification, and degree of eruption(DE) were as follow; Age(by #34) = 7.55 + 0.76Ks34 + 0.80DE34 - 0.72Ns34 Age(by #35) = 7.10 + 0.81Ks35 + 0.6IDE35 Age(by #37) = 6.61 + 0.82Ks37 + 0.5IDE37. Age(by #44) = 7.02 + 0.62Ks44 + 0.82DE44 Age(by #45) = 8.04 + 0.93Ks45 + 0.64DE45 - 0.89Ns45 Age(by #47) = 6.40 + 0.86Ks47 + 0.56DE47.