Surgical Orthodontic Treatment for Skeletal Class I with Facial Asymmetry and Occlusal Cant: A Case Report

2.1. Diagnosis and Etiology

The patient was a girl aged 20 years and 5 months who came for orthodontic treatment with chief complaints of anterior open bite and facial asymmetry (Fig. 1). The patient had no relevant family history and no medical or dental history of dental trauma. She had a straight profile and severe mandibular deviation toward the left according to the mandibular deformation in addition to occlusal plane canting and transverse dental compensation. The soft tissue vertical reference line was constructed as the line perpendicular to the interpupillary line [14]. The maxillary dental midline and the mandibular dental midline were deviated 1.5 mm and 7.5 mm toward the left of the facial midline, respectively. The soft-tissue menton deviated 12.0 mm toward the left. Intraoral examination showed Angle Class III molar relationship on the right and Angle Class I molar relationship on the left with minor crowding of both dentitions. Overjet was 0.2 mm, and the overbite was –2.5 mm.

Panoramic radiography showed no horizontal or vertical bone loss and normal root length (Fig. 2). The cephalometric assessment showed a skeletal class I relationship (ANB angle, 3.2°) (Table 1) with a high mandibular plane angle (FMA, 35°) and occlusal plane angle (Occ plane to FH, 15.0°). The mandibular and maxillary incisor inclinations were normal (FMIA, 56.2°; U1-FH, 113.6°). Computed tomography (CT) imaging showed marked menton deviation to the left (13.5 mm) (Fig. 3 and Table 2) and dental asymmetry associated with occlusal plane cant (bilateral differences in tooth height: U3-H, 0.9 mm; U6MB-H, 3.3 mm). In addition, the bilateral differences in coronal ramus angle (coronal ramus angle, 10.3°) and ramus position (Rma-S, 13.6 mm) were significant [15].

2.2. Treatment objectives

We made a diagnosis of skeletal class I malocclusion with mandibular deviation along with the maxillary canted occlusal plane. Treatment was performed to correct the facial appearance, improve the skeletal asymmetry, and establish appropriate incisor and molar relationships.

2.3. Treatment Alternatives

To achieve the treatment objectives, two possibilities were considered and discussed with the patient.

The first alternative involved combined fixed orthodontic treatment and orthognathic surgery by LeFort I osteotomy to correct the canted occlusal plane combined with BSSO for the asymmetric mandibular setback and maxillary first premolar extraction on both sides to correct maxillary incisor crowding. Extraction of both mandibular third molars would be necessary.

The second alternative involved combined fixed orthodontic treatment and orthognathic surgery by BSSO for the asymmetric mandibular setback. Maxillary first premolar extraction on both sides to correct maxillary incisor crowding and miniscrew implant anchorage would be used to correct the canted occlusal plane. Extraction of both mandibular third molars would be necessary.

After the two treatment plans had been explained to the patient, she selected the second option and provided informed consent to proceed.

2.4. Treatment Progress

The mandibular third molars (teeth 38 and 48) were extracted under general anesthesia before orthodontic treatment. The mandibular teeth were bonded with preadjusted edgewise brackets (0.022 × 0.028-inch slot), and the mandibular teeth were leveled and aligned using sequential nickel-titanium alloy wires. After extraction of the maxillary first premolars, a 0.022-inch slot preadjusted edgewise appliance was bonded to the maxillary teeth, and leveling and alignment were started using sequential nickel-titanium alloy wires. Next, a miniscrew implant 1.6 mm in diameter and 6 mm in length (Dual-top Auto Screw III; Jeil Medical, Seoul, Korea) was placed in the buccal region between the right maxillary second premolar and first molar (Fig. 4). The maxillary canines were retracted using a 0.016 × 0.022-inch stainless steel wire with elastic chains by application of intrusive force (250 g load). Then the maxillary incisors were retracted using sliding mechanics along a 0.018 × 0.025-inch stainless steel wire with nickel-titanium closed coil springs (250 g load). After presurgical orthodontic treatment for 26 months, orthognathic surgery with BSSO was performed. The mandible was asymmetrically set back 7.0 mm on the right side and 0 mm on the left side. Postsurgical orthodontic treatment was performed for 13 months, and then the fixed appliances were removed after a total treatment time of 3 years and 3 months (Fig. 5), and the patient received a maxillary wraparound retainer and mandibular bonded lingual retainer.

2.5. Treatment Results

The post-treatment records showed that the procedures resolved the occlusal cant and mandibular asymmetrical setback, improving the facial asymmetry (Fig. 5). The dental midlines were coincident with the facial midline, and proper class I canine relationships on both sides were achieved. The soft-tissue menton deviation was improved from 12.0 mm to 2 mm toward the left of the facial midline (Fig. 6). Panoramic radiography showed acceptable root paralleling without root resorption (Fig. 7). Cephalometric analysis (Fig. 7a and Table 1) and superimposition (Fig. 8) showed that a skeletal class I jaw relationship had been maintained (ANB angle, 5.0°), although the SNB angle was slightly decreased from 78.6° to 76.8° as a result of mandibular asymmetrical setback. The mandibular plane angle was increased slightly from 35.0° to 35.8° (FMA). The mandibular incisors were slightly proclinated from 56.2° to 53.6° (FMIA), and the maxillary incisors were slightly retroclinated from 113.6° to 111.6° (U1-FH).

The intrusion of the maxillary right dentition (N-side: U3-H 0.4 mm canine intrusion, U6MB 1 mm molar intrusion) and extrusion of the left dentition (D-side: U3-H 0.6 mm canine extrusion, U6MB 2.1 mm molar extrusion) resolved occlusal plane canting, contributing to facial asymmetry. Significant improvements were also seen in coronal ramus angle (N-side 78.0°, D-side 80.9°) and ramus position (Rma-H: N-side 55.9 mm, D-side 54.5 mm) after orthognathic surgery with BSSO.