a jaw advancer connects to the skull , maxilla jaw , and the jawbone , mandibular jaw , without contacting the teeth of a patient . each advancer , of a pair , has a hollow upper member with a head to admit a screw into the maxilla and an opposite threaded end , a socket having a threaded end that admits the upper member and an opposite smooth bore , and a lower member with a head to admit a screw into the mandible and an opposite smooth end that fits into the smooth bore . the lower member has a coaxial spring that provides an expansive force to the lower jaw and that cushions the socket . the lower member slides within the hollow portion of the upper member when the patient moves the advancer . the head of the upper member attaches proximate the molars of the maxilla to advance the mandible and attaches proximate to the incisors of the maxilla to retract the mandible . alternatively , the lower member has a slight curve to separate it from the teeth .