by Dr Leow Aik Ming
The essential role of masseter muscle is for adequate mastication (chewing). This bulky muscle is located laterally to the mandibular ramus, and thus plays an important role in facial aesthetics. Masseter hypertrophy is recognized as an asymptomatic enlargement of one or both masseter muscles. A hypertrophied masseter will alter facial lines, generating discomfort, and create negative cosmetic impacts in many patients. This leads to the prominent mandibular angle which is considered to be aesthetically unacceptable. The muscle function may also be impaired, thus resulting in conditions such as trismus, protrusion, and bruxism.
In most cases of masseter hypertrophy, it is bilateral and symmetric, but asymmetry is not unusual. In majority of the cases, the etiological factor is unknown therefore it is considered to be idiopathic. Unilateral occurrence can also be seen when patients chew or clench primarily on one side.
There are various treatment modalities for the management of masseteric hypertrophy. The aim of the treatment is to improve facial balance, change the shape of an overly square face and relief pain or discomfort as a result of an overly large masseter muscle.
The treatment modalities can be categorized into:
(A) Non-Surgical Treatment for Masseteric Hypertrophy:
Conservative management of the idiopathic masseter hypertrophy includes psychological counselling, use of mouthguards, muscle relaxants, anxiolytic drugs, analgesics, physical therapy, dental restorations, and occlusal adjustments to correct premature contacts. A good result can be achieved in the patients with mild hypertrophy but there is no reliable success rate of isolated clinical therapy. Injection of botulinum toxin type A (Botox) into the masseter muscle was considered as less invasive modality for the treatment of muscle hypertrophy. Local injection of very small doses of Botox into a muscle produces local paralysis and therefore, individual muscles can be selectively weakened and atrophy of the muscle occurs. Perhaps the biggest disadvantage of botulinum toxin therapy is that the treatment effect wears away and reverts to the original condition in 4 – 6 months. Unlike surgical excision of muscle tissue that reduces the actual number of muscle cells, botulinum toxin type A only reduces muscle volume temporarily.
(B) Surgical Treatment for Masseteric Hypertrophy:
This surgical treatment consists of removal of 3/4 to 2/3 of all muscle mass via intraoral approach. Occasionally, mandibular cortical bone or angle osteotomy can also be performed at the same time to achieve a streamlined jawline contour. The surgery to access the masseter muscles and the mandible (jawbone) is performed through incisions on the inside of the mouth, between the gum and cheek (lower buccal sulcus area), leaving no visible scarring. Once the correct amount of bone and muscle has been removed, the incision is closed with self-dissolving sutures. The result of surgical approach to masseteric hypertrophy is predictable and longer lasting compared to non-surgical method.