THE ROLE OF LATERAL CEPHALOMETRIC RADIOGRAPHY AND FLUOROSCOPY IN ASSESSING MANDIBULAR ADVANCEMENT IN SLEEP-RELATED DISORDERS

Mandibular advancement splints are successful in managing obstructive sleep apnoea (OSA) in selected subjects. For these to be effective, so me improvement in the dimensions of the oropharyngeal airway must occu r. Twenty subjects with proven obstructive sleep apnoea were examined using lateral cephalometric radiography and a fluoroscopic technique. Cephalograms were analysed, and assessed for both skeletal and soft ti ssue abnormalities known to be present in OSA subjects. On the basis o f these, a prediction was made as to whether the subject's oropharynge al airway would increase during mandibular protrusion. From the fluoro scopic sequences, the narrowest antero-posterior dimensions of the pos t-palatal and post-lingual airways were recorded as the mandible moved from the intercuspal position into maximal protrusion. The changes in airway size were noted and these were compared with the predictions m ade from the static films. In nine subjects, fluoroscopy indicated tha t the airway opened well during mandibular protrusion, seven did not i mprove and in four the changes were minimal. Post-palatally the mean a irway increase was 2.6 mm, whilst behind the tongue a mean improvement of 3.1 mm was seen. In all but two instances, the cephalometric predi ction agreed exactly with the outcome demonstrated by fluoroscopy. All subjects whose airways clearly increased were correctly identified by the cephalogram alone. Cephalometric features associated with a good airway response to protrusion were a reduced lower facial height, low maxillomandibular planes angle and a high hyoid position, accompanied by a normal anteroposterior relationship of the jaws, relatively norma l mandibular body length and soft palate area. The more abnormal the s keletal and soft tissue dimensions, the poorer the prognosis. Thus, wh ilst a single radiograph could indicate whether a positive mandibular response to protrusion could be expected, where doubt existed, a fluor oscopic analysis could provide a useful adjunct to diagnosis.