Different types of ccclusion in normal as well as in malocclusion during the primary dentition stage were investigated. A total of 155 plaster models was made from children,84 males and 71 females all of whom in the Hellman's dental age IIA stage(aged 3 to 5 years). The results were as follows.
1. The incidence of various types of occlusion was normal occlusion 56.8%, deep over bit 29.0%, open bite 7.7%, edge-to-edge bite 4.6%, progenia 1.9%, normal being the most frequent.
2. In considering the terminal plane of various types of occlusion, M-M step type was the most frequent, followed by V-V and D-D step types. In terms of age, V-Vtype had a tendency to decrease with age increase.
3. The most common terminal plane incidences of the various occlusal types were as follows: in normal occlusion, a V-V type, in open bite, an M-M step type or D-D step type, in edge-to-edge bite, an M-M step type, in deep over bite, a D-D step type and in progenia, an M-M step type.
4. In normal occlusion, V-V types tended to decrease with age. An increase of M-M step types among the 5-year olds in comparison to the 3-year olds was seen. For deep over bite cases, there was a tendency for D-D step types to increase with age.
5. In the maxilla, the total interdental spaces in all types of occlusion decreased among the 5 year olds more than among the 3 year olds. In the mandible total interdental spaces (in different types of occlusion) increased more among the 5 year olds rather than among the 3 year olds.
6. In the normal occlusion as well as in the deep over bite groups the M-M step type had the highest amount of total interdental spaces in the maxilla, the spaces being greater among the deep over bite groups (the latter). Total interdental spaces in the mandible among the two groups demonstrated no significant difference.