ABSTRACT
Variations in natural head posture (NHP) and hyoid bone (HB) positioning impart changes in the size and shape of the pharyngeal airways. In SAS, which was shown to be correlated with detrimental craniofacial anatomical conditions, control of pharyngeal permeability is lost during sleep. The aim of this study was determine if functional adaptation of NHP and HB position to these detrimental conditions could be observed, using Bonferonni probabilities, in a cephalometric comparison of 38 SAS adults in the wakeful state and a control group of 38 healthy adults. Since HB relationships with craniofacial anatomical structures vary with the positioning of the head, the cephalograms were taken according to the preliminarily tested NHP, thus making the method reproducible. In SAS craniovertical angulation was unchanged, but the head was maintained in a forward position (increased cervico-vertical angulation, P < 0.001). Maintenance of an acceptable pharyngeal permeability was associated with a more distant positioning of HB from the cervical column (P < 0.01) and from craniofacial references (P < 0.001). In spite of these facts lower pharynx opening was still reduced (P < 0.05). Soft palate and facial divergence were expectedly increased in the apneic group. All the individuals but one control could be correctly reclassified with the help of soft palate length, facial divergence, and two HB related variables. Prevention of pharyngeal collapsibility in SAS seems to be commonly associated with functional adaptation of NHP and HP position. The precise control mechanisms of this adaptation remains to be elucidated. Skeletal predispositions to SAS do probably develop already during infancy.
