3-dimensional positional analysis of mandibular segments after preorthodontic orthognathic surgery using intraoral vertical ramus osteotomy in class III patients

Abstract

The purpose of this study is to establish criteria on the predictability of preorthodontic orthognathic surgery (POGS) using intraoral vertical ramus osteotomy (IVRO) by measuring positional change of each bone segment immediately and 1-year after the surgery. Thirty-eight patients of skeletal Class III malocclusion who had two-jaw orthognathic surgery by the same surgeon were included in this study. The patients had menton deviation within 3 mm from skeletal midline, non-extraction orthodontic treatment, periodically taken multi-detector computed tomography (MD CT) data and no maxillofacial congenital abnormalities. Eight-teen patients who had orthodontic treatment prior to orthognathic surgery were included in the conventional surgery group (CS). Twenty patients who had surgery without presurgical orthodontic treatment were included in the preorthodontic orthognathic surgery group (POGS). Skeletal changes measured preoperatively (T0), two days after surgery (T1), and one year after surgery (T2) in two groups were compared using 3D CT. The results were as follows:

1. Proximal segment of mandible showed lateral (coronal, horizontal plane) and clockwise (sagittal plane) rotations, and mandibular condyle shifted in medial and anterior-inferior directions immediately after surgery. The movements returned to original positions, but not completely during the first year after the surgery. There was no significant difference between the two groups. 2. Posterior part of distal segment moved upward in the CS group, while both anterior and posterior part moved upward in the POGS group. Mandible rotated clock-wise in both groups. 3. The angle between distal segment and proximal segment 1 year after operation was greater in the CS group (9.1 ˚) compared to the POGS group (6.2 ˚). The rotation within matrix meant that POGS made the direction of the angle between two segments smaller compared to CS. 4. There was no significant difference of maxillary skeletal change between two groups. The maxillary second molars showed 1.2 mm, 1.32 mm intrusion during post-operative orthodontic treatment of POGS group.

Based on the results above, the change of proximal segment in the cases of POGS with IVRO on a patient with skeletal Class III malocclusion was not different from CS. If active physiotherapy is conducted using the conventional method, the proximal segment can be adapted in the physiological location regardless of the change in the occlusion. As POGS accompanies the movement of the distal segment itself as well as the teeth movement during the postoperative orthodontic treatment, and does not have an anterior occlusal stop, a close observation is necessary in order to prevent a formation of rotation fulcrum in an undesired location.