“Why Is One Side of My Jaw Bigger?” - Understanding Masseter Asymmetry

Noticing that one side of your jaw appears more prominent than the other? This is a common observation, particularly in the lower face and jawline. In many instances, the cause is not swelling or fat accumulation, but asymmetry of the masseter muscles.

The masseter is a key muscle used in chewing and clenching. When one side becomes more dominant or is overused, this may gradually lead to visible differences in lower facial width between the two sides.

Below are common reasons this can occur, and how qualified healthcare professionals may evaluate and address the concern.

1. Chewing Preference on One Side

Most individuals have a natural tendency to chew more on one side of the mouth. This long-term preference can result in unilateral hypertrophy of the masseter muscle.

Such asymmetry tends to develop gradually and may become more visible in photos or when clenching the jaw. Nilesh et al. (2021) described a case where habitual chewing on one side led to hypertrophy of the masseter muscle without any associated pain or dysfunction.

2. Bruxism (Teeth Grinding or Clenching)

Night-time teeth grinding or unconscious clenching during the day is a common functional cause of masseter overuse. If one side is more active, the resulting muscle growth can be uneven.

Research by Wu, Zeng, and Wu (2023) found that bruxism is a leading contributor to masseter muscle hypertrophy and can result in noticeable facial changes over time.

3. Bite or Dental Imbalances

Misaligned bites due to dental loss, jaw positioning, or restorative dental work may lead to one side of the masseter compensating more than the other. This can result in asymmetrical muscle development.

According to Sharma (2024), masseter hypertrophy may develop secondary to occlusal imbalance and may also co-occur with temporomandibular joint dysfunction (TMJD).

4. History of Injury or Surgery

Previous dental procedures, facial trauma, or uneven healing following surgery can affect how the jaw muscles are used, potentially leading to muscular imbalance.

How to Differentiate Muscle from Bone or Fat

If you gently clench your teeth and palpate both sides of your jaw near the angle, a firmer or more prominent side may indicate muscular activity. Fat generally remains soft and unchanged with movement, while bone remains constant regardless of clenching.

Clinical Management Options

If masseter asymmetry is contributing to discomfort or concerns about facial symmetry, a registered health practitioner may consider the following approaches:

• Behavioural and lifestyle adjustments to reduce muscle overuse

• Use of occlusal splints for bruxism management

• Bite assessment and treatment by a dental professional

• Botulinum toxin type A (BoNT-A) injections to reduce activity in the more dominant masseter muscle

The MSFIT injection technique has been discussed in the literature as a way to achieve both functional and aesthetic balance in the masseter muscle (Gewargis, 2025). Any treatment should be tailored to individual needs, and clinical suitability must be determined through professional assessment and informed consent.

When to Seek Professional Advice

If you are noticing new facial asymmetry, persistent clenching, or jaw discomfort, a consultation with a registered healthcare provider may be beneficial. At TT Aesthetics, our team will assess whether muscular factors are contributing and discuss management options suited to your individual presentation.

To learn more about your masseters book a consultation with a qualified expert, book TT Aesthetics.

TT Aesthetics Masseters Case Studies

Citations

Gewargis, J. (2025). Treating masseteric hypertrophy with botulinum toxin A: The MSFIT technique. Aesthetic Nursing, 14(2).

Nilesh, K., Dharamsi, R., Patil, P., & Mate, P. (2021). Management of unilateral idiopathic masseter muscle hypertrophy with botulinum toxin type A. BMJ Case Reports, 14(1), e239056.

Sharma, R. (2024). Masticatory muscle hypertrophy. Radiopaedia.

Wu, Y., Zeng, D., & Wu, S. (2023). Botulinum toxin type A for the treatment of masseter muscle prominence in Asian populations. Aesthetic Surgery Journal Open Forum, 5.