[Anodontia. 4: Crown shape of teeth of the anodontia with anhydrotic and hypohydrotic ectodermal dysplasia]

The purpose of this study was to investigate the morphological variation of teeth of the partial anadontia with anhydrotic and hypohydrotic ectodermal dysplasia. Qualitative and quantitative observations were made for the upper central incisor and upper first molar in the anadontia of 18 patients. Moreover, some phylogenetic consideration was taken on the variability of the shapes. The results were as follows. 1) The crown shapes of 28 upper permanent central incisors were classified into 5 types based on the presence and/or size of mamelons, from rudimental teeth such as the cone-shaped type to the almost normal but flat type. Also these morphological variation had a clear correlation to the number of unabsenced teeth of same side. 2) The relatively reduced mesio-distal size, which was said to be a strong trait which shows a tendency towards degeneration in human upper permanent molars, was not observed in the upper 1st permanent molar of the anadontia. 3) Of the 33 1st permanent molars, contraction of the hypocone and contraction of the metacone were independently found in 4 and 10 teeth respectively. 4) Protoconule, which are rudimental small cusps and mesial to the protocone, was observed in all 33 molars, and there was a correlation between the extent of their development and the number of remaining teeth on the same side. The relative length between the top of the paracone and protocone, also, correlated to the number of the remaining teeth of same side. 5) Morphological variations of the upper central permanent incisors and upper 1st molars of the anadontia reflected the phylogenetic process in human teeth to some extent. It seemed that the less was the number of remaining teeth of same side, the earlier phase it suggested in morphogenesis of human teeth.