Effect of mandibular position on three-dimensional shape of the oropharynx in seated posture

Dysphagia rehabilitation in the elderly includes direct therapy to alter the three-dimensional shape of the oropharynx so that food boluses can pass safely through the poorly functioning pharynx. Alteration of the mandibular position is thought to affect oropharyngeal shape, but this relationship remains poorly understood. We therefore studied the relationship between mandibular position and three-dimensional shape of the oropharynx in the seated posture normal for feeding. Ten healthy, dentate subjects participated (average age, 28·1 years). Experimental mandibular positions were the intercuspal position, bite-raised position and mandible-advanced position. The oropharynx was scanned in a 90° seated posture using dental cone-beam computed tomography, and the effects of changes in mandibular position were analysed after obtaining oropharyngeal volume, height, sectional area, average sectional area of oropharynx and the position of the epiglottis. Oropharyngeal volume and average sectional area increased significantly in the mandible-advanced position compared with other mandibular positions. Notably, the volume and average sectional area of the inferior part of the oropharynx increased significantly. Oropharyngeal height and sectional area at the base of the epiglottis showed no significant difference in bite-raised position and mandible-advanced position compared with intercuspal position. The position of the epiglottis moved significantly forward in the mandible-advanced position. The results of this study show that in a seated posture, volume of the oropharynx increases as a result of changes in the mandible-advanced position. The increase in oropharyngeal volume demands greater muscular constriction to generate swallowing pressure and could lead to a decrease in reserve capacity of swallowing.