Jawline Botox injections to reduce the masseter muscle to shape the face. Botox injection to the masseter is also a cure for teeth grinding. Strong masseter muscles give a wide jaw which in turn produces a square, masculine face. This can be unflattering for some women, and men too. Botox shrinks the masseter muscles and slims the face. The treatment involves three or four injections to each cheek. Botox is the only method of reducing the jaw without surgery.