Often, a square shaped jaw is due to the hyperactivity of the masseter (chewing) muscles. Frequent chewing of hard foods or grinding the teeth at night can cause the hypertrophy or overgrowth of these muscles. While often seen as an asset to a male’s appearance, a strong jaw on a female can be perceived as masculine. Reducing the size of the masseter muscles is achieved, over time, with the injection of muscle relaxants, giving a more feminine appearance.