Hard and Soft Tissue Changes following Orthognathic Surgery in Mandibular Prognathic Patients with Open Bite

Comparison between Two Jaw Surgery and One Jaw Surgery

Abstract

The purpose of this study was to evaluate hard and soft tissue changes in mandibular prognathic patients with open bite following different orthognathic surgery.
Twenty adult patients who underwent orthognathic surgery to correct mandibular protrusion and open bite were selected for this study. The subjects were divided into the following two groups based on surgical method: 12 subjects who underwent mandibular setback osteotomy with the sagittal split technique (one jaw group) and 8 subjects who underwent mandibular setback osteotomy with the sagittal split technique and combination (Le fort I and horseshoe) osteotomy in bimaxillary surgery (two jaw group). A pair of pre- and post-operative lateral cephalograms was used for hard and soft tissue analysis. Statistical analysis using a paired t test was performed for comparative study.
No significant differences were observed in the pre-operative anterior occlusion, dento-skeletal pattern and facial profile between the two groups. Anterior occlusion was improved in both groups following surgery and no significant differences were observed in the post-operative overjet and overbite between the two groups. However, significant differences were observed both in the dento-skeletal and facial profile changes between the two groups. The amount of mandibular up-backward movement, especially the chin portion in the two jaw group was significantly larger than that in the one jaw group due to the clockwise rotation of the maxillary occlusal plane following superior repositioning of the maxillary posterior portion. In accordance with this larger mandibular up-backward movement coupled with maxillary advancement in the two jaw group, more harmonized bimaxillary skeletal relationship as well as better facial profile were achieved in the two jaw group in comparison with that in the one jaw group. It is suggested that a combination of Le fort I and horseshoe osteotomy in bimaxillary surgery is a useful technique to treat mandibular prognathic patients with open bite.