The Treatment of Class III Malocclusion
with Anterior Cross-biteThis is a commentary on an article published in the December, 1999 issue of the AJODO. The article was by Deguchi and associates. In describing the type of Class III malocclusion the authors did not state that they were dealing with only anterior cross-bites, but all of the illustrations indicated that they were.
It is commonly known that the correction of anterior cross-bite Class III malocclusion and open bite Class III malocclusion is as different as night and day. In open bite Class III problems we avoid moving posterior teeth occlusally, while in Class III problems with anterior cross-bite we move the molars occlusally and swing the mandible down and back to correct the anterior cross-bite and the Class III molar relationship.
In the article under discussion it was stated that, "If the subject required control of the vertical growth of the mandible, a high pull chin cap was provided." In other words the authors considered it unwise to move molars occlusally.
In Article 23 of the Schudy Chronicles on the Internet is shown the records of a patient 36 years post treatment. This was a Class III anterior cross-bite malocclusion where the molars were moved occlusally to swing the mandible down and back to correct the cross-bite, the Class III molar relation, and create a beautiful face. The occlusion is shown 36 years post treatment and is almost perfect.
There are some very important principles involved in the treatment discussed in the article. Ten mm of articulare/menton distance increase resulted in only 4 mm of additional mandibular length. Since the gonion angle increased instead of decreasing (as it usually does), this produced an increase in mandibular length, and we would have hoped for a decrease.
In dealing with the correction of the Class III malocclusion with an anterior crossbite, there are two approaches - (1) correction by adjustment of the skeletal bones, and (2) correction by adjusting the dentoalveolar bone. The two approaches are radically different and diametrically opposite in basic principle. One stimulates alveolar bone and the other inhibits alveolar bone.
Apparently, when we try to prevent forward growth of the mandible by applying posterior and superior force with a chin cap, it has an adverse effect on the gonion angle - causing the angle to increase instead of decrease. Apparently, this posterior and upward force from the chin cap reverses the natural tendency of the gonion angle to reduce as it grows. This involves basic biologic phenomena, about which we have no knowledge at the present time.
The treated case shown in Article 23 of the Schudy Chronicles showed no effect on the gonion angle, and was corrected by stimulation of alveolar bone.
The point we would like to make clear is that Class III malocclusions with an anterior cross-bite require that the molars be moved occlusally instead of trying to prevent their vertical movement. This corrects the anterior cross-bite, the Class III molar relationship, and improves aesthetics.
Reference 1. T. Deguchi, DDS, MSD, PhD, T. Kuroda, DDS, PhD, N. P. Hunt, BDS, PhD, MOrthRCS, DOrthRCS, and T. M. Graber, DMD, MSD, PhD.
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