Hypertrophy (overgrowth) of the masseter muscles is a common condition that can result from a variety of habitual actions, such as excessive chewing force due to dental misalignment, teeth clenching during sleep, as well as teeth grinding during the day. The most common symptoms of masseter hypertrophy are jaw pain, TMJ, headaches, ear pain, neck pain, pain in the shoulders, feelings of tiredness in the jaw and discomfort while eating. Fortunately there are nonsurgical treatments for the elimination of masseteric hypertrophy, which not only decrease all previous symptoms, but also provide aesthetic benefit.

If we look at this video, it becomes clear how the masseter muscle, used for chewing, has become overgrown (masseteric hypertrophy)