Abstract
The extracted upper second deciduous molars, numbering 269, were classified into six types, type 1 to 6, according to the form of the occlusal surface. Relationships of each type with the tooth crown character and with the measurement value were examined. The results were as follows : 1. The frequency of the Type 3 (a rhombus) was the highest with 55.4%, followed by the Type 2 (a parallelogram) with 15.2%. These two types were the fundamental forms and the other types, the Types 1, 4, 5, and 6, were variations. 2. The tooth which doesn't present the differentiation of the distolingual cusp appeared most frequently in such special types as the Type 1 (a trapezoid) or the Type 6 (a triangle). 3. No relation was considered to exist between the occlusal surface form and the development degree of the oblique ridge. 4. Appearance of the Carabelli tubercle was most frequent in the Type 3. 5. In the relationship between the tooth size and the occlusal surface form, the Types 2 and 3 teeth, which are the fundamental forms, were smaller and the other types showed larger values. 6. Accordingly, it is considered that a deviation of the occlusal surface form in the deciduous molar bears no relation to degeneration phenomenon in the permanent tooth.
