[Morphological study of open bite. Skeletal Class I and Class II open bite]

The purpose of this study was to quantify the morphological features of class I and II openbite. The subjects were 151 female patients, over 7 years old, and as a control group, 180 female cases of normal overbite. The subjects were classified into 6 subgroups by ANB angles and ages as follows: 1. Class I A group (7 y less than or equal to age les than 10 y): openbite (30 cases), control (34 cases) 2. Class I B group (10 y less than or equal to age less than 15 y): openbite (23 cases), control (31 cases) 3. Class I C group (15 y less than or equal to age): openbite (20 cases), control (23 cases) 4. Class II A group (7 y less than or equal to age less than 10 y): openbite (38 cases), control (45 cases) 5. Class II B group (10 y less than or equal to age less than 15 y): openbite (20 cases), control (26 cases) 6. Class II C group (15 y less than or equal to age): openbite (20 cases), control (21 cases) The following results were obtained: 1. The combined features of class I and II openbite groups in all the 6 groups were an especially large anterior facial height and remarkable downward of lower occl. pl. angle. Mand. pl. angle was large, and the lower part of the face was tapered. 2. The primary factors of openbite were not only over-eruption of the upper molars but also vertical excess of the mandible with a large alveolar bone. 3. The clearest differences between classes I and II openbite were the mand. pl. and lower occl. pl. angles. The class I openbite groups had a large gonial angle, depending on the subgroup. On the other hand, the class II openbite groups exhibited backward and downward shifting of the mandible depending on the subgroup. 4. In the lower age groups (7 y less than or equal to age less than 10 y) both class I and class II openbite already had denture and alveolar factors, as well as skeletal problems. In the class II openbite, especially in adult cases there were unusual morphological problems both in antero-posterior and vertical relations. 5. Contrary to most reports, the nasal floor did not show an upward cant. In the adult class II openbite even a downward cant, resulting from the backward and downward shifting of the mandible was observed.