The immediate effect of changing mandibular position on airway and head position.

The principal clinician will perform all maxillo-mandibular (mx/md) registrations. The centric relation bite registration will be taken in the supine position following a method using an anterior jig. The posterior registration will be recorded using vinyl polysiloxone. The participant will be guided into the anterio-superior position and absence of pain on loading is confirmed. The phonetic bite position participants will have their mx/md relationship captured when they repeat the sound "Mississippi-miss" and the anterior position will be captured by asking them to close lightly onto a cylindrical object whilst the posterior teeth relationship is captured using vinyl polysilioxone. These registrations require 10 minutes disclusion of the teeth before each registration is recorded and repeated if inaccurate. The maximum intercuspal position does not need a recording. The cervical range of motion(CROM) device is fitted and after 15 minutes of habituation head position for one of the three maxillo-mandibular positions is read and immediately an airway test at the same head position using a pharyngometer at functional residual capacity is recorded three times and averaged. The other two mx/md relationships are recorded in the same way after 15 minutes of habituation.