[Longitudinal changes in the dentition of the deciduous reversed bite using plaster casts].

It is known that some of the deciduous reversed bite cases are corrected spontaneously by themselves. No decisive conclusion, however, has been achieved so far as to what morphological characteristics the self corrected cases have. The purpose of this study, therefore, was to determine whether the difference between the self corrected group (n) and the non-self corrected group (r) exists at their initial examination or if it occurs as a result of changes in occlusion. The materials used in this study were the serial plaster casts of 29 Japanese girls with the deciduous reversed bite at their first visit and these were measured with the three dimensional measurement system. The following results were obtained: 1. Characteristics of the initial examination with the n group: Overjet (-) and overbite in the n group were smaller than in the r group. The arch length and the perimeter of the maxillary dentition in the n group were longer, and the area of the incisive bone (U-C) was wider than in the r group. Moreover, the upper and lower canines in almost all of the n group cases were not touching each other and did not restrict mandibular movement, resulting in easy attrition for the deciduous anterior dentition. 2. Longitudinal changes in the n group: Mean change of this group showed a decrease in overbite caused by the attrition of the deciduous central incisors and the continuous eruption of the maxillary second deciduous molars. Overjet also decreased, because of an increase in the maxillary anterior arch length and of backward movement in the mandibular dental arch. Individual changes were much alike in mean changes in almost all of the measured items. Arch width between canines in the maxilla and arch length in the mandible decreased in some cases, suggesting that a discrepancy would occur when the permanent incisors erupt. 3. Longitudinal changes of the r group: Mean changes showed that overbite decreased in the same pattern as the n group, but overjet did not change and the mandible did not show backward movement. The reason was that overbite in this group was deeper than in the n group at the initial examination. Moreover, deciduous molar to molar width became wider to compensate the decrease in the arch length and the perimeter. Individual changes showed that some of the r group cases had a tendency to improve, but some became worse.