[Dental arch form achieved by orthodontic treatment]

The objective of this study was to compare the dental arch forms of a control group with normal occlusion to the finished dental arch forms achieved by orthodontic treatment. The data consisted of 185 Japanese males and 275 Japanese females. These sex groups were divided into three groups, i.e., a group treated by extraction of the four first premolars, a group treated by non-extraction method and a control group consisting of individuals with normal occlusion. Findings were as follows: 1. The position of each tooth showed a normal distribution, with a small range of variation in all groups. 2. There were no significant differences in the range of tooth distribution among the three groups in each sex. However, the measurement of the male values were larger than those for the females. 3. In comparison with the other two groups, the transversed width between the same number of teeth of the extraction group had a larger width in the anterior teeth segment and a smaller width in the posterior teeth segment. The non-extraction group had a larger width in all of the teeth segment except for the second molars, than for control group. There were significant differences in all of the teeth between the males and the females. 4. As a result of a qualitative and a quantitative examinations, it was determined that the dental arch forms were almost the same among the three groups for each sex. The dental arch became progressively longer in the following successive order for the extraction group, the control group and the non-extraction group. 5. Except for the intercanine width, the dental arch forms of the Japanese group were wider and longer than that of the Caucasian North American group. In spite of the variation of the genetic background in respect to the differences of the ethnic background and sex, it was confirmed that there were no noticeable differences in the dental arch forms between the orthodontically treated groups and the non-treated group with normal occlusion.