Methods for Correction of Mandibular Angle and Masseter Hypertrophy
Mandibular angle and masseter hypertrophy is also known as square mandible deformity. This kind of deformity generally manifests after the puberty development period, thus it does not lead to occlusion or masticatory function disorders. However, due to its specific facial appearance, it affects aesthetics. In recent years, there has been an increasing number of people seeking plastic surgery for this condition, especially young women. This article reports on a group of 15 cases that we surgically corrected in recent years. We analyze and discuss the clinical characteristics, surgical plan design, key points of surgical operation, and postoperative precautions for this deformity.
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1 Materials and Methods
1.1 Research Subjects
From 1987 to 1996, we collected data on 15 patients with mandibular angle and masseter hypertrophy who underwent our surgical correction. Among them, there were 4 males and 11 females, aged between 19 to 31 years old, with an average age of 25 years. All patients sought treatment to improve their facial appearance and requested to be reshaped into a "peach-shaped face." In this group of cases, 4 cases had one side of the mandibular angle and masseter hypertrophy more severe than the other, showing asymmetrical deformities; 3 cases had only unilateral hypertrophy while the other side was completely normal; and the remaining 8 cases had bilateral mandibular angle and masseter hypertrophy.
1.2 Clinical Characteristics
For those seeking medical help for mandibular angle and masseter hypertrophy, through routine clinical examinations, panoramic X-ray jawbone cephalometric radiographs, excluding tumors and trauma, all data were analyzed and studied. The characteristic manifestations of these patients include: (1) From the front view, the lower third of the face is significantly wide, forming a square face. (2) From the side view, the mandibular angle shows obvious bone hypertrophy, thickened like a bone tumor, abnormally enlarged. The thickness of soft tissue in this area also increases significantly, but palpation reveals that the soft tissue feels soft. (3) The GoGn-SN angle is too small, indicating that the inclination of the mandibular plane is too small. Some patients have over-correction of the lower third of the face, mainly manifested as vertical height developmental insufficiency of the chin, thereby exacerbating the square face deformity.
1.3 Treatment Plan Design
In designing the treatment plan for all cases, through formal psychological consultations with orthognathic surgeons and patients, we understand the patient's awareness of the deformity, motivation for seeking medical help, expectations for surgery, socio-economic status, and social adaptability. For individual patients with unrealistic treatment motives or excessively high expectations for surgery, they must be handled with caution; otherwise, unnecessary medical disputes may arise. When determining the amount of osteotomy and osteotomy line for the mandibular angle, the mandibular plane angle and the arc of the mandibular angle in the beautiful population are used as reference standards to depict the amount and route of bone cutting. Routine preoperative examinations are performed, preparing for intraoral surgery such as periodontal cleaning and handling dental caries and residual roots. Color photographs of the head and face from the front and side are taken.
1.4 Surgical Method
The intraoral approach starts parallel to the second bicuspid vestibule groove on the lateral side of the mandible, extending upward along the outer edge of the ascending ramus of the mandible, with a cut about 3-4 cm long. Subperiosteal dissection of the lateral soft tissues is performed. A specially designed retractor is placed laterally on the mandibular angle. Using the American-made Stryker series electric oscillating bone saw or high-speed bone drill according to the preoperative design, the hypertrophic mandibular angle is removed, making the post-resection bone end into the designed arc shape. When removing the hypertrophic masseter muscle, to reduce bleeding, a method of first suturing and then cutting is adopted. Postoperatively, drainage and pressure bandaging are applied.
2 Results
All cases had primary wound healing postoperatively. The postoperative effects were evaluated three months after surgery when the swelling had completely subsided. The evaluation criteria included the degree of satisfaction with postoperative facial shape improvement and the status of dentofacial functions. In this group of cases, all patients had normal postoperative mouth opening, type of opening, and chewing functions. Twelve cases were completely satisfied with the postoperative facial shape, two cases had slight left-right facial asymmetry, and one patient felt that insufficient tissue was removed.
3 Discussion
3.1 The characteristic square face deformity caused by mandibular angle and masseter hypertrophy, despite its unknown cause, is clinically considered a developmental deformity. After development is complete, the deformity no longer progresses. Some scholars believe it is related to excessive movement of the masseter muscle, such as individuals with bruxism habits or habitual teeth clenching during study or work being more prone to this deformity. For such patients, when forcefully clenching their teeth, a hypertrophied and protruding mandibular angle can be seen, palpable as a solid masseter muscle. This characteristic square face deformity, although less severe for men, is more difficult for women to accept. Therefore, among those seeking medical help, young women predominate. In this group of cases, 11 were female, accounting for the majority. Their purpose for seeking medical help was almost entirely to be reshaped into a "peach-shaped face" or an "oval-shaped face," which is publicly recognized as conforming to aesthetic facial beauty.
3.2 To reduce scarring and achieve cosmetic purposes, the correction of mandibular angle and masseter hypertrophy must be implemented intraorally. Due to the deep surgical position, narrow field of vision, and poor exposure, there is a possibility of osteotomy errors, such as the mandibular angle osteotomy line deviating towards the sigmoid notch or causing straight removal of the mandibular angle, thereby affecting the surgical outcome. Therefore, during the osteotomy process, to address this situation, we use a self-designed mandibular angle-specific retractor to expand the surgical field. During the surgery, continuous checks and adjustments are made to ensure a certain arc shape, restoring the deformed mandibular plane angle to normal. Additionally, a challenge in this surgery lies in the uniform osteotomy of both sides. During the operation, centered around exposing the mandibular angle, a point is defined at the posterior edge of the ascending ramus of the mandible, and another point is defined at the anterior edge of the mandibular body. Connecting these two points forms an arc-shaped line, which is the osteotomy line. During osteotomy, the direction of the drill bit or saw should be as consistent as possible on both sides, either entering vertically or obliquely according to the preoperative design, accurately removing the protruding mandibular angle and excising the hypertrophic masseter muscle, with mutual referencing between the two sides, ensuring that the postoperative mandibular angle resembles the normal arc-shaped line of the mandibular angle.