These bacteria that come from the food on the teeth and between the teeth are called "plaque" or "bacterial plaque" and also can cause the gums to become less healthy. "Gingivitis" which means gum disease is one type of disease that flossing helps to prevent. Very serious diseases can start on the teeth and move to the bone of the jaw, damaging the jaw badly. Flossing your teeth reduces the danger of these serious diseases of the jaw bone. These hard-to-cure jaw bone diseases are called "periodontal disease". 