A wide jawline is often caused by hypertrophic masseter muscles. Overgrowth of masseter muscles are caused by chronic teeth grinding, gum chewing or hard food chewing. With time, it will lead to excessive teeth wearing and chronic pain. By injecting botulinum toxin to relax the masseter muscles, the large muscle will decrease and shrink down in size over time. This will help to relieve chronic pain and slim down the jaw area and make the face appear slimmer.