1991 Volume 37 Issue 6 Pages 1129-1142
The position and size of the tongue and position of the hyoid bone in 35 mandibular prognathism patients (13 with open-bite and 22 without open-bite) were compared with those of 29 normal adults and their changes after oblique sagittal splitting osteotomy were analyzed longitudinally by cephalometric radiography with contrast media.
Preoperatively the anteroposterior and vertical dimensions of the tongue were similar to or smaller in both patient groups than normal. The anteroposterior dimension of the tongue was within the value of 2 SDs of the mean for all patients, and the vertical dimension of the tongue was within the value of 2 SDs of the mean for all patients except one. In all of the patients, the tongues were positioned anteroinferiorly and the hyoid bones were positioned anteriorly.
Accordingly, in most cases, the tongue was not important in the development of prognathism. Postoperatively the positions of the tongue and hyoid bone moved posteriorly and were not significantly different from their positions in normal controls.
After mandibular setback, an amount of the setback of the tongue tip was similar to that of the mandible, and an amount of the setback of the tongue root was half of that of the mandible. The reduction of tongue length immediately after operation was attributed to this difference in setback between the tongue tip and root. The increase of tongue height resulted from the inferior shift of the valiecula and the superior shift of the tongue dorsum. However, there was a difference between the two groups in the positional change of the mandible; rotation of the mandible in the group with opne-bite was counterclockwise and it was slightly clockwise in the other group. In the group without open-bite, there was correlation between the setback of the mandible and the changes of the tongue and hyoid bone, but correlation was slight for the group with open-bite.
In the time from immediately postoperative to one year after operation, although the mandible shifted slightly toward the preoperative position, the tongue was stable in size and maintained the position taken immediately after the operation, and the root of the tongue shifted without regard for the migration of the mandible.
According to these results the tongue was considered to have adapted to its new environment due to changing the position of its posterior part.
