Abstract
We evaluated quantitatively the lower permanent anterior crowding of 10cases after the chin cap treatment of anterior cross bite in the deciduous dentition (the chin cap group) and of 7 cases after the chin cap treatment in combination with an upper lateral expansion appliance in the deciduous and early mixed dention (the combination group), using their study models and lateral cephalograms. We also investigated the relationship between the degree of crowding and the dentitional and craniofacial morphology at the time of first visit and the amount of change.
The results were as follows;
1. We observed lower anterior crowding from 1 to 5 degrees in the 10 cases of the chin cap group.
2. In the same group, the amounts of expansion in the lower bicanine width and the lower anterior length following the exchange of incisors were remarkably inferior to the amount of expansion in the upper arch.
3. Based on multiple regression analysis in which the degree of crowding was a criterion variable, in addition to the difference between lower deciduous and permanent incisors and the craniofacial open bite tendency after the exchange of the lower incisors, the dentitional morphology in the lower anterior arch and their changing amount were selected as significant explanatory variables of partial regression coefficient.
4. In the 7 cases of the combination group, the appearance of crowding in the lower anterior arch was eased compared to the chin cap group.
5.1 year after the retaining of the expansion, the changing amount of the lower bicanine width concurrent with maxillary expansion was around the amount of corresponding to estimated growth, except unusual cases.
6. It is suggested that one of the reasons for the appearance of anterior permanent lower crowding after the treatment of anterior cross bite is a lack of the amount of the lateral expansion especially in the lower arch, and that active maxillary expansion is also effective for easing of the lower anterior crowding.
