Changes in alveolar morphology during open bite treatment and prediction of treatment result.

It has been postulated that dentoalveolar height is enlarged by a compensation mechanism in long face subjects. In this study, dentoalveolar composition was studied in 83 open bite patients. It was found that increases in overbite during treatment coincided with vertical lengthening of the symphysis, which exceeded increments in lower face height. This vertical growth coincided mainly with an increase in the area of the symphysis. Furthermore, a retrusion of the maxillary incisors enhanced bite deepening. Stability of the overbite during the retention period was studied in a subset of 22 patients. It was found that retrusion of the maxillary incisors during treatment led to a more stable overbite during the retention period. Vertical lengthening of the symphysis relative to the increase in lower face height seemed to enhance bite opening during retention. Prediction of the overbite may be reliable, if a re-evaluation of the patients takes place during active treatment. The angle NTGoGn had a substantial predictive value (multiple R = 0.46) for post-treatment overbite. It is concluded that in open bite patients, a dentoalveolar compensation mechanism results in a stable overbite at the end of treatment by enlarging symphysial height through a moderate increase in symphysial volume. In addition, retrusion of the maxillary incisors contributes to overbite reduction. However, an excessive increase in vertical height of the symphysis relative to lower face height may relapse after active treatment. For prediction of the post-treatment overbite, the angle NTGoGn may be used, although a re-evaluation during treatment is recommended.