The masseter is the large chewing muscle on the side of your jaw. If you often grind your teeth or clench your jaw, this muscle can grow larger. Your jawline then looks wider and more square. In a masseter treatment, a doctor injects a muscle relaxant into this chewing muscle. The muscle becomes less active and can gradually become a little smaller over a few weeks. This can make the lower part of your face look slimmer. Tension in the jaw and teeth grinding can also decrease.






