 Facemasks or reverse-pull headgear needs to be worn approximately 12 to 22 hrs to be truly effective in correcting the under bite, usually anywhere from 6 to 18 months depending on the severity of the bite and how much a patient is growing.The appliance normally consists of a frame or a centre bars that are strapped to the patients head during a fitting appointment.The frame has a section which is positioned in front of the patients mouth, which allows for the attachment of elastic or rubber bands directly into the mouth area.