When Botox is injected into the masseter muscle, the treatment is often called masseter Botox. It is also sometimes referred to as “teeth-grinding injections” or “jaw Botox.” The masseter muscle is a large, rectangular facial muscle that connects your lower jaw to your cheek bone and is the main muscle for chewing. Injecting botulinum toxin type A into the masseter blocks nerve cells to help relax the muscle. It is a highly effective treatment for patients who clench or grind their teeth or have been diagnosed with TMJ. Masseter muscle Botox is also popular non-surgical treatment to help reduce the width and shape of a square jawline — known as jawline slimming or facial slimming.