Abstract
The mandibular second milk molar tooth and the permanent fist molar are very similar in the morphology, and to the untrained eye they are liable to be mistaken one for another. The author measured various lengths of both teeth, and from this measurement the mean values of respective lengths and the indices thereof in both teeth were obtained. The morphological differences between both teeth were then statistically computed, and the results were summarized as follows. 1) In all the figures obtained from various parts of the crown the permanent first molar exceeded the second milk molar suggesting that the former was larger in size than the latter. 2) of all the values obtained that of bucco-lingual length was the largest, followed by that of longitudinal length of the crown in both teeth. 3) The ratio of the bucco-lingual to the mesio-distal length is smaller in the permanent first molar than in temporary second molar suggesting that the buccolingual length of crown is relatively well developed in the permanent first molar more than in the other. 4) Comparison of the ratio of the bucco-lingual to mesio-distal length in the cervical part of crowns of both teeth also show that the bucco-lingual length is relatively well developed in the permanent first molar more than in the other. 5) Comparison between the both teeth of the ratio of the bucco-lingual to mesio-distal length at the crown part to the same ratio at the cervical part showed that the ratio was larger in the permanent first molar than in the other suggesting that constriction at the neck of tooth was more severe in the second milk molar than in the permanent first molar. 6) The constriction, however, was more conspicuous in the bucco-lingual than in the mesio-distal length in the temporary second molar, and this relation was converse in the permanent first molar tooth.
