Abstract
The hypothesis that the third molar (M3) agenesis influences crown sizes and molar crown characters of the other teeth was investigated among the male groups in Japanese. One hundred and sixty nine individuals were divided into four groups: all the four third molars exist; agenesis of one third molar; agenesis of two third molars of both sides; agenesis of four third molars. Statistical analysis was applied on the upper or lower jaw independently.
Except for the upper lateral incisor, mesiodistal crown diameters of the remaining teeth were, in general, larger in the groups with the M3s agenesis than in that with the four M3s existence. Significant differences were found in the first and second molars of both jaws between the groups with four M3s agenesis and with four M3s existence. These results were explained by the mesiodistal compensatory interaction within the molar tooth row. Generally speaking, there was a tendency for the teeth of the M3s agenesis groups to be greater variability in size than those of four M3s existent group, and in M3 agenesis groups upper teeth tended to be more variable than lower teeth. However, there were no distinct differences in variability in each tooth group and in tooth number of congenitally missing in M3.
As for the molar crown characters there were no significant differences between agenesis groups and existent group in cusp number and groove pattern of the first molars of both jaws. In the second molars, the groups with four M3s agenesis had significantly higher values than the groups with four M3s existence and with one and two M3s agenesis only in incidence of the groove pattern like "X".
