Quantitative investigation on irregular cusps in lower permanent molars.

Abstract

The frequency of occurrence of anomalous cusps or tubercles on human lower first molars was investigated in three racial populations: Japanese, Australian Aboriginals and Dutch white. The technique used was moiŕe contourography, which permits the three-dimensional measurement of minute cusps. Four tubercles investigated were 6th cusp, 7th cusp, deflecting wrinkle and transverse ridge. The frequencies of four traits were all highest in Australian Aboriginals among three, especially those of 6th cusp and deflecting wrinkle were significantly higher than other two populations. Japanese and Dutch showed comparatively low frequencies of four traits, but the 6th cusp in the former occurred significantly higher than that in the latter. There was no significant differences of the frequency in all the traits between sexes. It was suggested that high frequency of these traits in Australian Aboriginals demonstrates the primitive morphology of the lower molar of this population.