[Morphological studies on the roots of lower first molars in Japanese]

Morphological observation of the roots of 2,164 lower first Japanese molars of known sex and side attributes, obtained from the collection of the Okamto Research Laboratory of Dentistry, produced the following results. 1. Roots varied from single to quadruple, but double roots were most common (70.6% in males and 83.4% in females). Next most frequent were triple roots 28.6% in males, 15.75% in females). Single-root was 0.7% in males, 1.1% in females. 2. Quadruple root occurred in only 1, male case (0.04% of the total). 3. Apical ramification occurred in 19.0% of all roots in the double-root category; 16.2% were ramifications on the mesial side only. In triple-root teeth, the ratio was higher: 21.9% for mesial roots. 4. Double-root teeth demonstrated 3 types of form of root apex pointed, rounded, and flat. These types were subdivided into 8 categories. The pointed type was most common (18.9% of the total) for both mesial and distal roots. 5. Orientation and curvature in doubler-root teeth (mesial and distal) were of 2 types. The separated type (Type I), in which the mesial and distal roots separate on the apical side, was most common (96.6% in males, 95.3% in females). 6. In triple-root teeth, size, orientation, and curvature of distal-lingual roots diversified into 8 types. Type V, in which lengths were about 2/3 that of the buccal root, size about half, and general curvature in the buccal-distal cheek plane with general straightness in the mesial-distal plane, was most common, accounting for 40.9% of the males and 47.0% of the females. 7. In double-root teeth, ramification degree between mesial and distal roots was 20.97 degrees in males and 18.97 degrees in females. In triple-root teeth the corresponding angles were 21.33 degrees in males and 18.98 degrees in females. In both cases, the angle was larger in male specimens. 8. In double-root teeth, root length was 12.75 mm in males and 12.41mm in females; root-trunk length was 3.22mm for males and 3.42mm in females. Differences between the sexes were significant in both cases. The root-trunk-length index was 25.24 for males and 27.56 for females, and the ratio of the length of root trunk to the root was 1/4. In triple-root teeth, root length was 12.66mm for males and 12.28mm for females; root-trunk length was 2.99mm for males and 3.21mm for females. The distal-lingual root length in triple-root teeth was 11.48mm in males and 11.10mm in females.(ABSTRACT TRUNCATED AT 400 WORDS)