Material and Method
Patient: A 27-year-old woman
First visit: March 13, 2012
Primary complaint: Hoping to get treated for micrognathia and malocclusion
Family history and medical history: No special notes
Current medical history: On March 13, 2012, she visited our hospital with a primary complaint of micrognathia and malocclusion. We referred to an orthodontist for the diagnosis of her jaw deformity and preoperative orthodontic treatment. When she returned to our department on March 10, 2013, after the completion of the preoperative orthodontic treatment, she complained of drowsiness during daytime. Therefore, we referred her to the sleep outpatient department, where the Epworth Sleepiness Scale (ESS) score was recorded at 14 points and the apnea–hypopnea index (AHI) was 22.5/h, based on which moderate OSA was diagnosed.
Present illness: Systemic findings: Nutritional status was good, height was 163.6 cm, body weight was 61.8 kg, and body mass index was 23.0 kg/m2, indicating the absence of obesity according to the criteria 4) of the Japan Society for the Study of Obesity.
Extraoral findings: Her face was symmetrical and long, the lateral side of the face was convex with marked mandibular retraction, and the chin was markedly retreated. The upper lip measured 14.3 mm, and the lower lip measured 21.4 mm, protruding from the E-line (Fig 1A). No clicking sound or pain was found in the temporomandibular joint.
Intraoral findings: The occlusal state revealed angle II grade on both sides, the horizontal overlap was +3.0 mm, the vertical overlap was −2.0 mm, and the maximum opening was 32 mm (Fig 1B). The exposed gingiva of the maxillary anterior teeth measured 5 mm.
No abnormal findings were detected in the size or morphology of dentition and tongue, and no hypertrophy was observed in the uvula or palatine tonsils.
Imaging findings (Mar 14, 2013): Three-dimensional computed tomography (3D-CT) images revealed absorption images on both mandibular condyles. The distance from the highest point to the mandibular notch at the mandibular condyle was 12.5 mm on the right side and 8.3 mm on the left side (Figs 2A, B).
In the cephalometric analysis, SNA (81°) was within the reference value, and SNB (69°) was smaller than the reference value. The ANB (12°) was larger than the reference value, the facial angle (68°) was smaller than the reference value, the maxilla was within the reference value, and the mandible was in the posterior orientation (Table 1, Fig 3A).
The moderate OSA diagnosed in the sleep outpatient department and the absence of obesity or palatine tonsil hypertrophy suggested that the morphological abnormality of the mandible, termed as small mandible, is the major cause of OSA.
Clinical diagnosis: micrognathia, malocclusion, open bite, OSA, progressive condylar resorption (PCR).
Treatment plan: In this patient, the gingival exposure of the maxillary anterior teeth was as large as 5 mm, and the mandibular angle was large, and a long face was observed due to occlusal insufficiency due to small mandibular disease and open bite. Hence, the purpose was to improve the occlusal insufficiency and aesthetics. The patient received LF+HS on the maxilla, the palate and dentition were divided into horseshoe shapes, and the maxillary gingival fragments were planned to be elevated by 5 mm in the maxillary molars, 7 mm in the anterior teeth, and counterclockwise.
There are two possible conditions for mandibular surgery in this patient: SSOR, which moves the mandible forward, and MDO, which extends the mandible forward. In this case, absorption was observed in both mandibular condyles before surgery, and hence when the mandible was rapidly moved anteriorly by SSRO, the mechanical burden on the mandibular condyle was large as indicated by Shimizu et al [5]. It is considered that there exists a high possibility that PCR will progress after surgery due to a decrease in blood flow from soft tissues due to mechanical stimulation. In contrast, MDO was selected because it is recommended as a method that can reduce the mechanical burden on the mandibular condyle and maintain blood flow to the mandibular condyle with minimal periosteal detachment. In addition, one of the complications of MDO surgery has been reported to be postoperative relapse [6,7]. Therefore, in consideration of relapse, we planned to perform overcorrection to extend the mandible to the incisal occlusion position. We decided to obtain a stable jaw position by tightening the occlusion through postoperative orthodontic treatment. Furthermore, extending the mandible anteriorly expands the tongue anteriorly and extends the tongue anteriorly, so that the anterior–posterior diameter of the pharynx behind the tongue also increases, and improvement of OSA can be anticipated. We explained to the patient and her parents before surgery that the surgical procedure involves cutting and lifting the upper jaw and extending the lower jaw forward and that there is a risk of surgical complications including PCR and relapse. The patient and her parents were also informed regarding the prolonged hospitalization, and their consent was obtained. Moreover, if she still felt the mandibular retraction after surgery, GP can be used to move the chin forward to eliminate the mandibular retraction. Regarding the administration of GP, we decided to consult again after the operation based on the result of the operation.
Treatment and course: On May 10, 2013, both LF+HS and MDO were performed.
Intraoperative findings of LF+HS and MDO: For LF+HS, we first performed a conventional Le Fort I type osteotomy, and after down fracture, we avoided the descending palatine artery and performed anterior osteotomy of the maxillary sinus floor from the outside, and then performed an osteotomy crossing the anterior nasal cavity floor. We then divided the dentition and palatine bone pieces into horseshoe shapes. The dentition fragments were raised 7 mm upward for the maxillary anterior teeth and 5 mm upward for the molars, and we fixed the maxillary dentition fragments to the lateral edges of the left and right piriform apertures and the lower alveolar ridge of the left and right zygomatic bones using Stryker U-CMF plates and locking plates.
After dividing the mandible into sagittal planes, we attached a Zurich distractor Lamas type Y-shaped plate manufactured by KLS Martin to the mandible and extended the extenders on both sides by 3 mm to complete the operation.