The Frequencies of Accessory Tubercles and Other Traits in the Upper Deciduous Second Molar.

Small irregular cuspules or tubercles are often seen on the occlusal table of the human deciduous molar as well as the permanent molar. These frequencies were investigated semi-quantitatively with the use of moire contourography. The moire photographs of the occlusal surface were taken with the tips of the paracone, protocone and metacone aligned in a horizontal plane parallel to the grating of the moire contourography. Contour interval was set at 0.2 mm. The frequency of occurrence of a tubercle was counted in three grades according to its contour patterns. Materials were Japanese deciduous upper second molars of 23 males and 33 females with negligible attrition. The frequencies of appearance of tubercles were as follows (sexes pooled): (1) mesial paracone tubercle, 62.5%; (2) mesial accessory tubercle, 76.8%; (3) protoconule, 19.6%; (4) lingual paracone tubercle, 87.5%; (5) metaconule, 26.8%; (6) distal accessory tubercle, 14.3%; (7) CARABELLI's cusp, 82.1%; (8) buccostyle, 17.8%. The incidence of the traits was compared with those in the permanent first molars previously studied. The traits nos. 4, 5, 7 and 8 were significantly more frequent in the deciduous molars than in the permanent first molar, when tested by x2 test. On the other hand, the traits nos. 1, 2, 3 and 6 which located on the mesial and distal marginal ridge did not show significant difference between both molars. This suggested that there might have been differences of phylogenetical origins between traits on the marginal ridge and those in the occlusal table and/or on buccal and lingual surfaces.