Condylion/Gnatheon Growth
The subject of condylion/gnatheon growth is one of considerable importance to the development of the lower face and the treatment of Class II malocclusion.
This study revolves around the importance of posterior horizontal condylar growth. It is hereby postulated, that Nature adjusts posterior horizontal growth and the size of the gonion angle to keep the growth of the face integrated as the individual face grows.
We will use the growth records of two individuals to illustrate this important concept. Both of these subjects were studied from approximately 8 years to 16 years. They did not receive orthodontic treatment.
We could find no references in the literature to this subject; therefore there is no bibliography listed. The diversity of posterior horizontal condylar growth and variability of the gonion angle seems to have been necessary in these two male subjects to produce reasonably normal and acceptable profiles and dental conditions.
By superimposing the two mandibles on the mandibular planes and registering on the lingual cortical plate of the symphysis it is shown that horizontal condylar growth varied widely in the two subjects. Please see Fig. 1. It is also shown that the closure (reduction) of the gonion angle played a leading role in the process. One individual had a handsome profile, while the other one had an acceptable profile. I regret that we do not have facial photos.
Fig. 1:
Should it appear to the reader that there may be an error in the measurement of vertical condylar growth, it must be remembered that vertical condylar growth is measured with relation to the mandible, while effective vertical condylar growthis measured from the gonion angle to sella horizontal.
As shown in the illustration, horizontal condylar growth varied 14 mm between the two subjects. One had 9 mm of posterior condylar growth, while the other had 5 mm of anterior condylar growth. It would be reasonable to assume that these different growth processes were the result, not cause of facial changes.
As stated above, the reduction of the gonion angle played an important role in these harmonious growth processes. In one individual, the gonion angle was reduced 10°. This caused the mandibular plane to change 20° (26° to 6°), in one individual as opposed to 4° in the other. Were it not for the adjustability of the gonion angle, such adjustment of the condylion/gnatheon distance would not have been possible.
The direction of horizontal condylar growth caused 15 mm of anteroposterior effect on the position of the
chin. Vertical condylar growth of the two individuals caused a 5 mm difference vertically. The closure of the gonion angle, was associated with approximately a 5 mm reduction of the length of the condylion/gnatheon distance in one individual, while in the other the reduction was negligible.
Thus the variation of the horizontal condylar growth and the
variability of the reduction of the gonion angle, taken together,
is a marvelous phenomenon which helps control the length of the
mandible - helps to harmonize the growth of the cranio-facial
system. The horizontal condylar growth moves the chin forward and the
variability of the gonion reductions keep it from moving too far
forward. The give and take between these two forces helps to
harmonize the growth of the lower face.
While horizontal condylar growth has been thoroughly discussed,
its complexity has by no means been fully recognized. We are
still learning more about the causative origin of this growth.
In article five there was found a high correlation between the
vertical growth of the lower molars and posterior horizontal
condylar growth. This lead to the postulation that vertical
lower molar growth partially causes posterior horizontal growth
of the condyles. Now we have recognized that there is an abstruse relationship
between the horizontal condylar growth and the reduction of the
gonion angle.
Posterior horizontal condylar growth projects the chin forward
and the reduction of the gonion angle keeps the chin from moving
too far forward--the resultant of the two forces determines the
antero-posterior position of the chin. In addition to this
phenomenon, we must compare the effective vertical condylar
growth and the vertical molar growth, to determine the vertical
position of the chin.
Obviously, the difference of the direction of the growth of the rami renders it difficult to compare the two subjects; however, Dr. Beni Solow has taught us that the angle of rami is relatively constant throughout growth. Therefore we are assured that the measurements in the inset are correct. If the mandibles were positioned more nearly as they exist in the natural state, then there would be no illusion.
To study only the effects of growth is to place the "cart before the horse," and to let the "tail wag the dog." It is simply unacceptable for an advanced discipline such as Orthodontics!!
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