A radiographic study of tongue posture at rest and during the phonation of /s/ in class III malocclusion.

In this investigation a group of individuals with Angle Class III malocclusions were studied radiographically to determine their tongue posture at rest and during phonation of /s/. Their speech and hearing was also evaluated. All of the subjects had normal hearing, while eleven of the twelve in the group showed some degree of sibilant distortion. At rest, these Class III subjects demonstrated a tongue posture that was lower than normal and more retruded. During the phonation of /s/ these individuals also demonstrated retrusion of the tongue in an apparent attempt to achieve a normal relationship of the tongue tip to the maxillary anterior teeth, an increased amount of mandibular depression, and a greater than normal distance between the tongue tip and the mandibular anterior teeth. Despite the compensatory movements exhibited by these individuals with Class III malocclusions, normal /s/ production was found in only one of the twelve subjects studied. This is in contrast to the successful compensations that result in normal /s/ production seen in a great number of individuals with a Class III, Division 1 malocclusion, as demonstrated by Subtelny, Mestre and Subtelny.