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Jaw Reduction (Slim Face Surgery)

The mandible is also called the “jawbone.” Its posterior parts are mandibular condyles, which are hidden next to the earlobes and are components of the temporomandibular joint. From the mandibular condyles, the mandible (ramus of the mandible) extends downward to the angle of the mandible and then turn forward by 90° to form the body of the mandible, ending at both sides of the chinbone (mandibular symphysis). There are many soft tissues surrounding and covering the mandible; the thickest ones are the masseter muscles that affect the width of the lower face. Several people will try to slim their faces by injecting botulinum toxin before taking the decision to undergo mandible reduction. However, botulinum toxin injection is not a permanent solution because it can only reduce the muscle thickness and result in a slightly slimming face without effectively and persistently improving the true conditions of the outward extending or protruding mandible. In particular, over-slim and depressed cheeks due to botulinum toxin overdose can highlight the undesirable contour or angle of the mandible. Patients whose square-shaped faces are caused by an outward extending mandible should consider undergoing mandible reduction to permanently fix the problem.

As a normal ratio, the width of the mandible should be smaller than that of the zygomatic bone so that the facial contour from the top to the bottom in the front view is an oval shape. If the width of the forehead, which is the distance between both lateral edges of the brow ridges, is chosen to be the reference width, the perfect ratio between the width of the mandible and that of the forehead should be 0.8:1. If the real ratio is higher than that, the lower face will look fleshy or outward expanded. There are two main conditions that will cause the mandible to look protruding or wide: one is that the mandible angle are outward extending or protruding and the other is that the mandible body together with the angle is hyperplastic and hyperosteogenic. In the first condition, patients’ lower faces show the protrusive angles in the side view and look wide and angled in the front view so that the shape of the entire face looks rectangular like a “home plate.” In the second condition, patients’ mandibles will gradually become wider from the angles to the sides of the chin; the jawline in these patients can be too long, and the distance between the mouth corners to the jawline will be too wide. Some patients in a worse situation can even have a protrusive chin. According to the clinical experiences and observations, Dr. Chuang noticed that the mandible protrusion in most patients is caused by these both conditions; Dr. Chuang needs to perform extensive bone cutting to achieve obvious and effective results.

In the modern technique, the incision site of mandible bone cutting is always located in the intraoral lower gum; the length of the incision is only approximately 3–5 cm, which will slightly differ depending on the area and range of bone cutting. The main goal of this procedure is reducing the front width of the lower face and diminishing the side contour of the protrusive angles. Because this surgery will make the jawline soft and smooth and also makes the face slim and pointed (“V” shape), it is also called slim face surgery or “V-line” mandible reduction. The masseter muscle covering the mandible can simultaneously become atrophic due to a deficiency of bony support, so patients will never need a botulinum toxin injection in the future. If the masseter muscle is obviously hypertrophic, which will probably affect the reduction result or even induce bone regrowth, Dr. Chuang can also remove a part of the masseter muscle to obtain a stable long-term result. Dr. Chuang currently provides three different mandible reductions for patients:

Mandible Angle Resection

Mandible Angle-Splitting Osteotomy

Mandible Bone Shaving

Comparison of various mandible reductions

Mandible angle resection Mandible angle-splitting osteotomy Mandible bone shaving
Ideal candidates Mild or moderate square-shaped face or wide face/severe side protrusion Moderate or severe square-shaped face, heavy round face Mild wide face with masseter muscle hypertrophy
Procedure range Mandible angle Mandible angle and outer cortex of mandible body removed from the angle to the side of the chin Mandible body and part of the angle
Procedure duration (h) 2 2.5 1~1.5
Recovery from the procedure (days) 5~7 7~10 3~5
Masseter muscle removal No No Yes
Face slimming result Moderate Perfect Little/unobvious
Extent of face slimming/side 0.5~0.8 cm 0.8~1.0 cm 0.3~0.5 cm
“V-shaped” result Unobvious Obvious None
One side correction No Yes Yes
Bone regrowth Rare No Maybe
Chin numbness Rare Often Almost none