A Roentgenographic Study on the Development of Roots of Mandibular Permanent Posterior Teeth

하악영구구치 치근발육에 관한 방사선학적 연구

In order to evaluate the correlation of age with development stage on permanent lower posterior teeth. the author exmined the roentgeregrams in standard films taken by intraoral technic and analysed the development phases of 1358 teeth of 500 males ranging from 9 to 15 years. The development was divided into 7 phases : Crown complete (Cr. C.). Root length 1/4(R. 1/4) Root length /2 (R. 1/2) Apical closure complete (A.C) The obtained results were as follows : 1. The formation of roots in full length on posterior teeth was complete as follow : a. Roots of 1st premolar : 12.72 years b. Roots of 2nd premolar : 12.94 years c. Meral Roots of 2nd molar : 13.38 years d. Distal Roots of 2nd molar : 13.46 years 2. The formation of apical forman of premolar was closured as follows : a. Apical foramen of root of 1st premolar : 13.64 years b. Apical foramen of root of 2nd premolar : 13.93 years 3. As a general rule. the mesial roots of second molar were developed earlier than distal roots of second molar. 4. In the correlation of age with the development stage, the regression equations. the correlation coefficents. and the sample numbers were “Y = 0.8370x + 10.2160, r = 0.71(p<0.01), n = 318”on lower first premolar, “Y = 0.6984x + 10.2148, r = 0.71(p<0.01), n = 385”on lower second premolar, “Y = 0.8810x + 10.2040, r = 0.65(p<0.01), n = 344”on mesial Root of lower second molar, and “Y = 0.7310x + 10.7940, r = 0.66(p<0.01), n = 311”on Distal Root of lower second molar respectively.