Cuspal Ridges of Deciduous Upper Second Molars in Japanese Subjects

The occlusal surfaces of deciduous upper second molars were photographed by moire contourography using the standard trigonal plane. The ridges of a cusp, omprising a central ridge and the mesial and distal accessory ridges, were identified by the patterns of the moire fringes. The central ridge was present on all cusps except for the hypocone in both sexes. Frequencies of the two accessory ridges on trigonal cusps exceeded 60% except for the distal accessory ridge on the etacone. The mesial accessory ridge on the metacone was significantly more common in females than in males, but the running pattern of the cuspal ridges showed little difference between sexes. The oblique ridge of the deciduous molar was well developed compared with that of the permanent first molar. This ridge was observed in all subjects, but its height and structural components varied remarkably. A small tubercle on the oblique ridge was sometimes observed, usually located on the metacone side. This tubercle was similar to the metaconule in its position and morphology. Intercuspal distances showed larger mean values in the molars with a metaconule than those without. This implied that the overall crown size was affected by the degree of development of some crown components, such as the ridges and tubercles.