[Morphological study on open bite patients].

The purpose of the present study is to investigate the morphological features of open bite patients who have also disharmony of anteroposterior relations between maxilla and mandible. Lateral head films of 40 adult females with open bite were used. The samples were classified into three groups by ANB angle. Three groups were as follows. 1. Type I open bite (12 subjects, 1 degree less than or equal to ANB less than or equal to 4.5 degrees). 2. Type II open bite (13 subjects, ANB less than 4.5 degrees). 3. Type III open bite (15 subjects, ANB less than 1 degree) The normal samples was the longitudinal data of females in our department. Skeletal and dental variables were calculated and compared norm versus type I open bite, type I open bite versus type II open bite and type I open bite versus type III open bite, respectively. The following results were obtained. 1. Disharmony of the vertical dimensions in type I open bite was mainly due to long anterior lower facial height which was accompanied by large gonial angle as compared with norm. 2. There were no difference in anteroposterior position of the maxilla and nasal floor in all three open bite groups. 3. There were no difference in anterior and posterior facial height between type I and type II open bite. However, type II open bite showed the backward rotation of the mandible accompanied by over eruption of upper first molars. 4. Type III open bite showed longer anterior lower facial height which was caused by excessive mandibular growth than type I open bite. 5. Upper incisors showed labial inclination as compared with norm in all three open bite groups. However, lower incisors showed labial inclination in type II open bite and lingual inclination in type III open bite as compared with type I open bite. As a result, the inter-incisal angle was small in type II open bite and large in type III open bite as compared with type I open bite. These results suggested that the dentoalveolar factors were large in type II open bite and the skeletal factors were large in type III open bite as compared with type I open bite.