Background

Understanding the factors that determine mandibular positioning enhances one's ability to identify the retrognathic mandible and its effects on the upper airway. The mandible articulates with the petrous portions of the temporal bones via bilateral temporomandibular joints. The size, location, and orientation of the petrous portions of the temporal bones affect the position of the mandible in both anteroposterior and superoinferior planes of space.1 The base of the skull, therefore, is the first variable affecting mandibular positioning. From this articulation forward, the size and morphology of the mandibular condyles, rami, bodies, and symphysis determine the size and position of the mandible relative to the cranial base. This size and position have been shown to have important effects on the upper airway2 via various mechanisms. One such mechanism is that of tongue position. Tongue position is affected by virtue of the space available for the tongue to rest as dictated by mandibular size, and by the genioglossus muscle3 pull, which is affected by the anteroposterior location of the genial tubercles located on the lingual cortex of the anterior mandible. Other means by which mandibular position affects the upper airway are by various muscle attachments from the mandible to other structures that affect the airway. Most important are the attachments of the genioglossus muscle, the genio-hyoid muscle, and the anterior bellies of the digastric muscles.4

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