Jaw reduction or Mandible angle reduction is a type of surgery in which the objective of treatment is to narrow the lower one-third of the face—particularly the contribution from the mandible and its muscular attachments. There are several techniques for treatment—including surgical and non-surgical methods. A square lower jaw is generally considered a very masculine trait, especially in Asian countries. If the lower third of the face is wide, it can create a rather square-shaped appearance to the face as a whole or can distort the natural appearance of the angle between the chin and the neck. Whereas square lower jaws are often considered a positive trait in men, a wide mandible can cause significant facial discordance and/or masculinization of the female face. Even in certain men, the size of the lower jaw can cause facial disharmony—particularly when there is asymmetry.
A wide lower face can primarily be caused by a wide mandibular bone or over-sized masseter muscle. Over-sized masseter muscle can be resolved with the use of botox injections whereas having a wide mandibular bone requires surgical intervention to reduce the size of the bones.
Consultation and patient evaluation
An enlarged mandible could be caused by various developmental or congenital disorders, or some rare disorders such as acromegaly. However, in the Asian population, the facial structure (typically classified as brachycephalic), wide zygoma and mandible arch is a common feature. 
Prior to selection of a treatment, the patient is examined to determine whether the wide jaw is due to the bone size, the masseter muscle or both. Three-dimensional analysis of the clinical photos, X-rays and 3D CT scans from the front, lateral, oblique, basal and overhead views are required for a detailed evaluation.  The level of protrusion of the mandible angle, the size of the masseter muscle and the overall structure of the jaw are evaluated. Based on the analysis and face-to-face consultation, the surgery plan can be created to produce the desired aesthetic results. 
Surgical techniques are used to directly reduce the size of an enlarged mandible. Depending on the candidate's individual facial structure, either mandibular resection can be performed alone or in conjunction with a sagittal mandibular reduction. 
A guarded oscillating saw is first used to mark the proposed osteotomy line to avoid excessive resection of the mandibular bone. Following this process, the bone resection is then performed with the appropriate size of oscillating saws. Additional sagittal spilt ramus resection can be performed using a burr. 
Inferior alveolar nerve is the most important anatomic structure during mandible reduction surgery and great care should be taken to avoid injury to this nerve. Potential complications include injury to the inferior alveolar nerve which provides permanent numbness and damage to the lower lip and even death.
Another factor to consider is the mentalis muscle which elevates the lower lip and chin. During the surgery, the mentalis muscles should be carefully reattached after the mandible bone has been excised. Failure to reattach the mentalis muscles will lead to the chin and lower lip to sag, causing permanent damage.
Common symptoms include haematoma, infection, asymmetry, over- or under-correction of the mandibular bone, sensory deficit. Excluding asymmetry and over- or under-correction, the other symptoms dissipate within three to six months post-surgery.  Individuals with abundant soft tissue or thick skin may consider an additional lifting procedure done simultaneously with the jaw reduction surgery, as there is a high possibility of sagging soft tissue. Age and skin elasticity level also determines whether a lifting procedure is required.
Non-surgical techniques are essentially limited to cases in which the masseter is enlarged. While a masseter muscle can be large due to congenital reasons, it can commonly be an acquired deformity. Like any muscle it increases in size with exercise. Behaviors such as repeated gum chewing, teeth clenching, or bruxism can contribute to enlargement of the muscle.
A convenient method to treat an enlarged muscle is through the use of botox injections. Botox is injected into the enlarged muscle, weakening it so it slowly becomes smaller through atrophy over several months. There is no down-time and improvement is gradual—individuals who interact with the patient may never know that a plastic surgical procedure was performed
The use of Botox for jaw reduction has been studied scientifically. Improvement is generally not seen for at least 2 – 3 weeks. Peak improvement occurs at months 3 to 9 with good results still observable at one year in many patients.
The procedure can result in temporary paralysis of the muscles that move the lips, a rare, but danger acknowledged complication.
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