Poster 41: Stability of Anterior Open Bite Correction in Class III Patients Using Bimaxillary Surgery Involving Intraoral Vertical Ramus Osteotomy

Abstract

There is currently limited data on the use of intraoral vertical ramus osteotomy (IVRO) in the surgical treatment of anterior open bite and class three malocclusion. The purpose of this study is to investigate the stability of Le Fort I osteotomy with IVRO in the correction of anterior open bite with concomitant class III malocclusion. Chart reviews of patients who underwent surgical correction of anterior open bite with class three malocclusion were obtained from the years 2004-2009. Preoperative, postoperative, and 1 year postoperative lateral cephalograms were obtained. Anterior open bite was measured clinically from the edge of the maxillary central incisor to the edge of the mandibular central incisor along its axis. Angular measurements were used to evaluate jaw movement in the horizontal and vertical directions. Anterior-posterior movement of the jaws was determined by changes in the SNA and SNB angles. Vertical movements of the maxilla were calculated from changes in the Maxillary Occlusal Plane (MOP) and Palatal Plane (PP) angles to SN. Mandibular vertical movement was based on changes in the mandibular plane (MP) angle to SN. Dental compensation was determined by changes in MOP and MP angles. All cephalograms were traced and measured digitally with Dolphin© software. Statistical analysis was performed with the SAS procedure PROC MIXED (SAS/STAT software, SAS institute Inc., Cary, NC, USA). The accuracy of landmark identification, superimposition, and measurements were confirmed by retracing all cephalograms 7 days later by the same investigator. Sixty patient records were identified with 27 meeting the inclusion criteria. Six patients failed to have positive incisal overlap at 1 year postoperative (23%). Comparing preoperative data between the 2 groups, patients in the relapse group had a more significant open bite (OB −6.07 mm vs. −3.48 mm, p<0.05), overjet (−2.14 mm vs. −0.79 mm, p<0.05), maxillary posterior vertical excess (SN-PP: 0.75° vs. 3.74°, p<0.05), and a steeper mandibular plane angle (SN-MP: 41.98° vs. 36.35°, p<0.05). Surgically, the relapse group also had more maxillary clockwise movement compared to the non-relapse group (SN-PP +5.72° vs. +3.39°, p<0.05), but less mandibular counterclockwise movement (SN-MP −0.93° vs. −2.46°, p<0.05). When separating patients based on the severity of their preoperative open bite: no patients failed in the mild group (1–3 mm open bite; 0/9, 0%), 3 patients failed in the moderate group (3–6 mm open bite; 3/13, 23%), and 3 patients failed in the severe group (>6 mm open bite; 3/5, 60%). IVRO, when performed with maxillary Le Fort I osteotomy, has a success rate (78% positive incisal overlap at 1 year post operative) that is comparable to other surgical techniques when treating patients with anterior open bite and concomitant class III malocclusion. Patients likely to relapse have a severe preoperative open bite, a high preoperative mandibular plane angle, or inadequate mandibular counterclockwise movement during surgery. This study provides an evidence-based alternative to current techniques.