1981 Volume 6 Issue 3 Pages 136-143
The purpose of this study is to survey concerning the frequencies and pathogenic factors of malocclusion on 2325 children (1202 boys and 1123 girls) to live in Yahaba district, Iwate prefecture.
Results of the examination were as follows:
1) Frequencies of normal occlusion were 41.2%, and malocclusion were 58.8%, especially, the crowding appeared at the highest (23.9%) among these malocclusion.
2) Frequencies of crowding increased transiently at the stage of the eruption of permanent incisors, thereafter once decreased, this recured increasing due to the eruption of buccal teeth and second molars.
3) Frequencies of maxillary protrusion increased through dental age Ⅱ C to ⅢB, from at this time these malocclusions appeared to fix the abnormalized shape and size.
4) Frequencies of reversed occlusion showed a maximum at the stage of the eruption of permanent incisors, but after these stage, the frequencies decreased.
5) The complete eruption of four second molars appeared at high rate in normal occlusion rather than malocclusion (P<0.05).
In the reversed occlusion, the eruption of lower second molars showed significantly (P<0.01) high rate compared with upper one.
