Abstract
Abstract: A phenomenon of regressive tendency on the morphogenesis of the lower second molar roots in mice was investigated using the seven inbred mouse strains which had differences in the rate of incidence for the occurrence of the Gutter-Shaped Root(GSR). Also we identified a criterion in order to evaluate the GSR using seven inbred mouse strains. Consequently the following conclusions were obtained:
1) We could divide the subjects into three types, type I (two roots), type II (incomplete GSR) and type III (complete GSR) as a degree of the fusion of the root in seven inbred strains. In two strains, C 57 BR and C 57 L, which had a high frequency for the occurrence of GSR, it was showed that there was a high percent of the type III. On the other hand, two strains, A and C 57 BL, apperaed only type I.
2) In the seven inbred mice, there were observed no significant differences based on sex, on the lower second molar root length in both the lingual and the buccal aspect.
3)Statistical differences were observed between the root length of the C 57 BR, C 57 L, and AKR strains and those of the A, C 3 H, C 57 BL, and RF strains (P<0.05). The root length of the C 57 BR, C 57 L, and AKR strains were much longer than those of the A, C 3 H, C 57 BL, and RF strains. The root size of the former three strains did not show trends toward reduction.
4) Accordingly, as the coefficients of variation were considerably low in both the lingual and the buccal aspect on the root length, it is suggested that the root lengths in inbred mice are little influenced by environmental factors.
