Treating Masseter Hypertrophy: Professional Tips

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Last Updated On: 2024-01-26

Masseter muscle hypertrophy and lower face contouring can be safely, effectively, and non-invasively corrected using BTX injections.

Doctor Medica team

What is the use of botulinum toxin?

Botulinum toxin (BTX) is a powerful neurotoxic protein that is produced by Clostridium botulinum bacteria, a type of microorganism that is found abundantly in soil and untreated water throughout the world. Though the BTX is highly toxic to humans, the toxin is now used widely in the medical industries to successfully treat various medical conditions caused by excessive muscle tone and uncontrollable muscle contractions, including blepharospasm, strabismus, cervical dystonia, hemifacial spasms, juvenile cerebral palsy, and adult spasticity. In the past two decades, the neurotoxin has undergone extensive research and has garnered interest for its applications in the field of aesthetic medicine. Many cosmetic and therapeutic indications associated with pain, uncontrollable muscle contractions, and hypersecretion of certain glands can now be treated successfully with BTX.

What is mechanism of action of botulinum toxin?

Botulinum toxin is renowned for its extremely potent muscle relaxing activity. The toxin functions by inhibiting the release of the neurotransmitter acetylcholine from nerve terminals at the neuromuscular junction. This results in temporary inhibition of muscle contractions and movements. Besides that, the neurotoxin also induces local chemical denervation of parasympathetic postganglionic cholinergic fibers, which is ideal for managing conditions associated with gland hypersecretion, such as hypersalivation and hyperhidrosis. Also, clinical studies found that BTX may be efficient at treating medical conditions like bruxism, myokymia, and anal fissure. In addition to relaxing muscles by preventing the release of a neurotransmitter, clinical studies also suggested that BTX may alleviate pain by altering the normal pain mechanism. The analgesic effects of BTX were first observed in patients who reported substantial pain-relief in regard to their cervical dystonia. Though the pain reduction mechanism was initially associated with reduced muscle hyperactivity, other animal studies demonstrated that BTX does exert a direct analgesic effect. This discovery paved the way for other health indications that may also be managed with BTX, such as headaches, migraines, neuropathic pain, myofascial pain, and chronic lower-back pain. While the outcomes are positive, in-depth research is necessary to ascertain its safety and efficacy in these respects. Current evidence shows that the neurotoxin can interrupt the spasm-pain cycle and selectively weaken painful muscles. Botulinum toxin type A is widely used in Asia, especially among Asian women who dislike a square face shape and prefer an ovoid face shape, to manage masseter hypertrophy and correct lower facial contouring.

What is masseter muscle hypertrophy?

The masseter muscle is located laterally to the mandibular ramus and is one of the four major muscles involved in mastication (chewing). Besides playing an important role in mastication, the masseter muscles are also vital for determining facial aesthetics. Enlarged and hypertrophied masseter muscles will only alter the facial lines, resulting in less than desirable facial asymmetry and a square face shape, which is usually considered a masculine attribute. Though a well-sculpted jawline is often regarded as the epitome of youth and beauty, a square jawline may appear too conspicuous and out of proportion with other facial features. In fact, some communities greatly favor an oval, delicate, and feminine facial shape, as reported by Baek et al. This is true for Korean women, who are genetically predisposed to have a wide jawline. Unfortunately, a broad jawline is not well-favored, as there is a belief that it could bring bad luck. This cultural belief, together with the social preference for slim and smaller faces, causes many people to resort to remodeling treatments for the lower facial region. Masseter hypertrophy is actually a rare condition that is characterized by benign unilateral or bilateral enlargement of the masseter muscles, as first described by Legg in 1880. Masseter muscle hypertrophy may be caused by chewing gum habits, dietary habits, and bruxism (teeth grinding). This condition develops without any symptoms, and most patients usually seek aesthetic treatment to sufficiently correct any obvious asymmetry caused by unilateral presentation.

How is masseter muscle hypertrophy diagnosed?

For masseter muscle hypertrophy to be successfully corrected, it is very important that a correct diagnosis is made based on extensive assessment. Indeed, swellings at the angle of the mandible can be caused by the following reasons:

  1. Compensatory hypertrophy (due to hypotrophy or hypoplasia in the contralateral side);
  2. Neoplasms of soft tissues;
  3. Masseter muscle intrinsic myopathy;
  4. Masseter tumor;
  5. Parotid tumor;
  6. Parotid inflammation;
  7. Salivary gland disorder;
  8. Odontogenic problems.

Masseter muscle hypertrophy, in addition with bruxism and regular clenching of the jaw, can lead to toothache, tooth wear, tooth fracture, temporomandibular joint pain, masticatory muscle pain, and tension-type headaches.

What is the treatment for masseter muscle hypertrophy?

Since masseter muscle enlargement is actually a benign condition, its treatment is generally quite unnecessary and only conducted for aesthetic purposes. The angles of the jaw can be expertly sculpted and contoured via surgical and non-surgical methods. Patients opting for the surgical method to contour their prominent mandibular angle will have their masseter muscles partially excised. Osteotomy, which is the surgical reduction of the thickened bone in the mandibular region, can also be performed with excellent results. That being said, these invasive surgical procedures have their own drawbacks, such as a long recovery time and health complications that can include nerve injury, facial nerve paralysis, infections, hematomas, trismus, uneven contour line, asymmetric resection, and sequelae from general anesthesia administration.

The nonsurgical approach to correcting masseter muscle hypertrophy involves injecting BTX into the affected muscles to induce disuse atrophy. The intramuscular injection of the toxin solution will de-bulk the muscles and further reduce the width of the lower face. Since the introduction of BTX injection as the functional treatment of masseter hypertrophy by Moore and Wood in 1994, many subsequent clinical studies have highlighted the benefits of this procedure. Research done in 1998 demonstrated the efficacy of BTX type A for the aesthetic volume reduction of the enlarged muscles. Besides that, an article in 2001 regarding the usage of BTX for the correction of masseter and temporal muscles. In 2005, a total of 1,021 patients were successfully treated with BTX type A to reduce the volume of the masseter muscle. This particular research concluded that BTX type A injection is a simple technique that can actually replace surgical masseter resection and it minimal side effects and reduced downtime. The clinical study also detailed weekly progression of BTX type A in injected masseter muscles. The weekly progression occurred as follows:

  1. Week 1: Muscles start to soften;
  2. Week 2 to 4: Muscles are noticeably thinner;
  3. Week 10 to 12: Maximum effect of BTX are delivered to the muscles;
  4. Week 12+: Muscles regain their action;
  5. Week 16+: Muscles regain their volume.

What is bruxism?

Bruxism is a condition where the affected patients excessively and involuntarily grind their teeth and clench their jaws. This condition has two main types: nocturnal bruxism, which typically occurs during sleep, and awake bruxism, which occurs during wakefulness. While the exact cause of bruxism remains unknown, experts claim that this oral parafunctional activity may happen due to a combination of physical, psychological, and genetic factors. Patients with bruxism display symptoms such as fractured or chipped teeth; increased toothache; tired or tight jaw muscles; pain in the jaw, face, or neck; headaches; and even sleep disruption.

What is the treatment for bruxism?

Bruxism can be treated via BTX type A injections into the affected masseter muscles, which will reduce pain and the occurrence of grinding episodes. Though there is insufficient scientific evidence to support the efficacy of BTX in treating bruxism, current clinical studies and literature reviews have demonstrated reduced repetitions of bruxism episodes, decreased bruxism-associated pain, and high patient satisfaction following BTW administration. The possible mechanisms of action of BTX in reducing the severity of bruxism are myriad; some of them include the following:

  1. Direct anti-proprioceptive effects on nerves;
  2. Direct effects at the neuromuscular junction;
  3. Blockage of the propagation of afferent nerve impulses;
  4. Inhibition of the release of necessary neuromodulators and neuropeptides.


Masseter muscle hypertrophy and lower face contouring can be safely, effectively, and non-invasively corrected using BTX injections. Besides that, BTX injections can also be used as an adjunct therapy for treating bruxism. Prior to conducting either procedure, both the physician and the patients must consider important issues like the formation of neutralizing antibodies that may interfere with the outcomes and long-term cost effectiveness.

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