Severe skeletal Class III malocclusion with an anterior open bite poses a treatment challenge, and involves anterior, posterior, transverse, and vertical control of the teeth and skeleton. In the evaluation of the anterior-posterior aspect, two-jaw surgery with maxilla advancement can resolve midfacial deficiency. Two-jaw surgery is also recommended over one-jaw surgery for greater ANB angular correction, particularly in cases with severe skeletal Class III discrepancy.6
Clockwise rotation of the MMC and occlusal plane can correct the proclination of the upper incisors and can improve the flat smile arc.7,8
In addition, clockwise rotation of the MMC can lead to a greater amount of mandibular setback and improved facial esthetics.7,9
Due to the invasive nature of two-jaw surgery, several studies have suggested the use of maxillary molar intrusion with temporary anchorage devices as an alternative to LeFort I osteotomy for maxilla impaction.10,11,12
However, maxillary molar intrusion cannot resolve midfacial deficiency and poses the risk of apical root resorption.13
In this case, we performed two-jaw surgery with maxilla advancement and clockwise rotation of the MMC to achieve better esthetic results.
From the transverse view, in patients with mandibular prognathism, some studies have noted the development of buccal tipping of the upper posterior teeth and lingual tipping of the lower posterior teeth, to maintain masticatory function.14,15
In skeletal Class III patients, transverse dental compensation is closely related to sagittal and transverse skeletal discrepancy.16
In surgery-first orthognathic cases, dental compensation of the upper and lower posterior teeth in the transverse section may cause occlusal interference during surgery.17
After surgery, the inter-arch cross-elastics were applied to correct the transverse dental compensation of posterior teeth. The posterior open bite was setup for surgical occlusion was to avoid unpredictable occlusal interference and unexpected post-surgical anterior open bite.
In a vertical view, open bite can be categorized into skeletal open bite and dental open bite. However, it is difficult to make a differential diagnosis between these categories, because the clinical features often entail a combination of both factors.18
Hence, evaluating soft tissue, skeletal features, as well as dental features can clarify the identification of an open bite tendency.19
The etiologies of an anterior open bite are mainly classified into three groups: anatomical, environmental, and genetic factors.18
In the present case, the anatomic features of the skeletal open bite were an abnormal lower gonial angle value and overbite depth indicator (ODI) as shown in Figure 6 and Table 2
A greater lower gonial angle indicates more vertical growth of the mandible and an increased lower anterior facial height.25
In terms of environmental factors, tongue thrusting was observed, along with step-up in the upper anterior incisor region; ,the open bite was mainly limited at the anterior teeth. To resolve the habit of tongue thrusting, we bonded a lingual button over the palatal side of the upper incisor as a reminder of tongue position. During orthodontic treatment, we guided and checked the patient’s tongue position at every appointment. The use of positioners for finishing or retention offers advantages in preventing open bite.26
No genetic factors were involved, based on the family history of this case. Hence, we corrected the anterior open bite with clockwise rotation of the maxilla by LeFort I osteotomy. Another factor influencing post-surgical instability was posterior facial height (PFH) enhancement.27
In our case, we retained PFH to achieve a stable result.
When deciding between surgery and orthodontic camouflage treatment for skeletal Class III patients, the patient’s chief complaints, facial profile, limitation of teeth movement, and severity of bony discrepancy should be taken into consideration. A recent study reported six cephalometric measurements (overjet ≤ -4.73 mm; Wits appraisal ≤ -11.18 mm; L1-MP angle ≤ 80.8°; Mx/Mn ratio ≤ 65.9%; overbite ≤ -0.18 mm; and gonial angle ≥ 120.8°) that can be used to determine whether surgical intervention is appropriate in borderline cases.28
Surgical treatment is recommended if the patient meets at least four of the six criteria. In this case, the patient met four of the criteria (overbite: -1 mm, Mx/Mn ratio: 61.6%, Wits appraisal: -15 mm, gonial angle: 122°) and she agreed with surgical orthodontic treatment.