Leveling the Maxillary Occlusal Plane without Orthodontic Appliances in Patients with Hemifacial Microsomia Using Unilateral Vertical Mandibular Distraction Osteogenesis

PURPOSE:

Internal distraction for mandibular lengthening using a vertical vector (vMDO) has been shown to be a stable procedure in the mixed dentition stage for patients with hemifacial microsomia (HFM). Orthodontic appliances have historically been employed to improve the occlusal plane and stability of the maxillary dentoalveolar unit after distraction, but these devices require considerations of cost and patient compliance. The purpose of this study was to evaluate the ability to align the maxillary occlusal plane using vMDO without orthodontic appliances in patients with HFM.

 

METHODS:

This was a retrospective evaluation of consecutive patients over an 18-month period who underwent unilateral vMDO for the correction of vertical mandibular asymmetry secondary to HFM with Kaban-Pruzansky type II mandibular deformities. Patients were included if they had complete records and at least one year of clinical follow-up post-consolidation. Preoperative PA cephalograms were analyzed using known landmarks for vertical and horizontal reference lines to record ramus height, maxillary height, dentoalveolar height, chin point deviation, occlusal height, and occlusal plane cant. These values were compared to post-distraction measurements from PA cephalograms taken at a minimum of 3 months after consolidation.

 

RESULTS:

Over an 18-month period, 5 patients met inclusion criteria; 3 subjects were female, median age was 12.6 years. Median distraction length was 21.3 mm. Median radiological follow-up was 6 months (range 4 to 38 months) post consolidation. There were no major complications during the study period. Ramus height on the distracted side was increased a median length of 12.0 mm (range 6.2 to 18.6 mm), corresponding to a median ramus height differential (non-distracted minus distracted side) improvement of 98%: median ramus height differential 15.0 mm (range 7.4 to 22.4 mm) preoperatively and 0.25 mm (range 0.2 to 13.1 mm) at follow-up. The chin point distance from vertical midline was improved by 29.1%: median chin point deviation of 7.35 mm (range 4 to 11.6 mm) pre-operatively and 5.55 mm (range 2.7 to 7.8 mm) post-operatively. The maxillary height differential (non-distracted minus distracted side) leveled by a median of 55%: median maxillary height differential 3 mm (range 1.8 to 4.2 mm) pre-operatively versus 1.35 mm (range 0.2 to 2.5 mm) at radiological follow-up. The maxillary occlusal height differential (non-distracted minus distracted side) was decreased by a median of 44.7%: median occlusal height differential of 3.8 mm (range 1 to 5.9 mm) preoperatively and 2.1 mm (0.3 to 2.8 mm) at radiological follow-up. The occlusal plane cant angle was decreased by a median of 84.6% toward neutral: median occlusal cant of 8.5 degrees (range 7.4 to 10.1 degrees) preoperatively and 1.3 degrees (0.8 to 2.8 degrees) at radiological follow-up.

CONCLUSIONS:

Unilateral vertical mandibular distraction osteogenesis improves mandibular ramus height and chin point deviation, while also effectively leveling the maxillary occlusal height and cant angle for patients with HFM without the need for an intraoral orthodontic appliance. Future study will be aimed at assessing the long-term stability of these promising results.