Dento-facial Changes following Orthognathic Surgery of Mandibular Prognathism with Open Bite

Abstract

This study was undertaken to extract characteristics of dento-facial vertical changes following orthognathic surgery in mandibular prognathic patients with open bite and to clarify morphological factors that affect the stability of postoperative occlusion.
Lateral cephalometric radiographs were taken in a sample of adult mandibular prognathic patients with (Open bite group) and without (Control group) open bite. Each group consisted of 12 subjects who underwent mandibular setback osteotomy with the sagittal split technique requiring intermaxillary fixation with circumferential wiring. There were no significant differences in the A-B difference and overjet in the pretreatment stage between the two groups.
Dento-facial vertical changes were divided into three subgroups changes in denture and skeletal patterns, as well as in an anterior occlusion (a combination of denture and skeletal patterns). These changes were analyzed and compared between the two groups in five stages: Pretreatment, immediately before and after surgery, posttreatment, and under retention (more than one year after posttreatment). The results were as follows:
1. During the preoperative orthodontic treatment period, the Open bite group showed an elongation of upper incisors (P<0.01), an upward displacement of the Menton (P<0.01) and an increase in overbite (P<0.001) as compared with those of the Control group.
During the intermaxillary fixation period, both groups showed an elongation of upper and lower incisors, an upward displacement of the Menton and an increase in overbite. The Open bite group revealed a smaller overbite than the Control group immediately after surgery (P<0.05).
During the postoperative orthodontic treatment period. the Open bite group showed an elongation of lower incisors (P<0.05). The Menton was displaced mainly downward in the Open bite group. The overbite decreased in the both groups.
During the retention period, there were no changes in the denture pattern in both groups. The Open bite group showed a downward displacement of the Menton and a decrease in overbite.
2. No significant effects on dento-facial patterns in the pretreatment stage were observed, dentofacial changes followed preoperative orthodontic treatment and osteotomy on the postoperative dentofacial changes were demonstrated in both groups. However there was a correlation between the overbite in the pretreatment stage and its change during the retention period in the Control group (P<0.01). Regarding the relevancy of each subdivided dento-facial change in the postoperative stage, there were correlations between the skeletal pattern and the anterior occlusion in both the Open bite (P<0.001) and Control (P<0.05) groups during the retention period.