Abstract
In orthodontic treatment for maxillary protrusion, markedly larger lingual displacement of the anterior teeth is necessary than for other cases, and for skeletal mandibular protrusion, surgical retraction of the mandibular bone is frequently carried out. These treatments will reduce the tongue space and cause the tongue to change its form and position, which may result in a potential constriction of the pharyngeal airway. The constriction of the airway is a serious problem in orthodontics since it has been considered to affect the dentofacial morphology or dental arch morphology inducing malocclusion. In this study, therefore, the correlation between pharyngeal airway and dentofacial morphologies was determined and the effects of the experimental reduction in tongue space on the morphological changes in pharyngeal airway were examined by lateral reontogenocephalograms. The results obtained were as follows : 1. In simple regression analyses, all the correlation coefficients found between the items in pharyngeal airway and dentofacial morphologies were not larger than 0.681 and none of the former items might be characterized by any particular single item of the latter. 2. The multiple regression analyses showed that the morphology at the upper portion of the pharyngeal airway was dependent on the variables representing downward growth of the mandibular bone. 3. When the tongue space was reduced by 5 mm as in the lingual displacement of the anterior teeth, significant changes were found in the pharyngeal airway such as the anteroposterior constriction at the middle to lower portion, the reduction in area at the middle portion, and the superioinferior extension at the lower portion. 4. The 10 mm reduction in tongue space as in the surgical retraction of mandibular bone caused significant morphological changes in the pharyngeal airway one to two times as large as those in the case of 5 mm reduction. Significant decrease was also found in the superioinferior dimension of the airway at the middle portion. The foregoing findings indicate that it may be useful for a good orthodontic performance to pay attention to the morphology of the pharyngeal airway in diagnosing and to estimate its changes by the reduction in tongue space in planning the treatment.
