Orthodontic braces are designed to treat mal occlusion - crooked teeth (crowding of teeth) are the most common reason for the fitting of fixed braces. To date, orthodontic appliances have used a ligature (a small rubber band that holds the orthodontic arch in place and causes the teeth to move into the desired position) to function. Nowadays, self-ligating appliances - which do not have ligatures - are also used in treatment . Functioning is based on the action of flaps that hold the orthodontic arch in the brackets.