It seems important to futher explore the role of horizontal condylar growth in shaping the lower one third of the face. Vertical condylar growth has been comprehensively discussed and its role in shaping facial anatomy should be well known.While horizontal condylar growth has been thoroughly discussed, yet in more recent time we have added a new aspect to this discussion. Since horizontal condylar growth is a separate entity and participates importantly in shaping facial form, it seems appropriate to discuss it as comprehensively as possible.

Condylar growth is a key player in producing lower facial form. It has two components -- vertical and horizontal. Their effect on facial anatomy depends on the relative amounts of each. To describe effective condylar growth strictly correctly, it is growth activity between sella horizontal and the gonion angle, measured perpendicular to Frankfort.

Both vertical and horizontal growth have their functions. Vertical condylar growth per se has the function of moving gonion downward and the chin forward, conditioned by the vertical growth of the molars. Posterior (horizontal) condylar growth per se has only one function -- to move the chin forward. Forward condylar growth has the function of moving the gonion angle down, around the upper molar teeth and ultimately moving the chin forward, and is conditioned by the vertical growth of the molar teeth.

In a period when the molar teeth exhibit no growth and the condyles continue to grow (which frequently happens) we can begin to understand cause and effect -- we begin to understand why the chin changes its position in a given manner. Then when we add another dimension by noting the effects of horizontal condylar growth, we begin to widen our understanding of the intricacies of jaw growth.

Horizontal condylar growth is only a part of a very complex system but it is unique. Why? Because it can be accurately measured, not being a part of any other measurement.

In four different approaches of trying to analyze the growth of the jaws, we came up with a high degree of association between the horizontal growth of the condyles and the vertical growth of the lower first molars. This was a surprise. We never would have suspected that we would find such an association.

First: In the 62 subject matrix, ages 7 to 16 years, we found a correlation of 0.64, with a probability of 0.000, between the SNB difference between time one and time two and horizontal condylar growth. In the growth group of 50 in the same study we found the correlation to be insignificant between the horizontal condylar growth and the vertical growth of the lower first molar at the one percent level of confidence (R = .32). While in the treated group of 62 the correlation was .48 with a probability 0.001. We take this to mean that since treatment almost always causes vertical growth of the lower molars, this vertical development partially causes an increase in horizontal condylar growth.

The student T test reading for horizontal condylar growth between the control group of 62 subjects and treated group of 50 subjects was 3.70 with a p. value of .001. This indicates that treatment tends to cause horizontal condylar growth.

Second: In the 95 subject matrix, a random sample ages 6 to 17, we found an R. of .3281 with a probability of .001 between horizontal condylar growth and vertical growth of the lower first molar. Also we found an R. of -.6928 and a P. value of 0.000 between the ramus to Frankfort angle and the vertical growth of the first molar. A high angle between the ramus axis and Frankfort usually indicates a low angle type of face where lower molars have failed to grow vertically. Thus, this combination of increments produces a high negative reading.

Third: The posterior movement of gonion is consistent with the findings of Bjork's implant studies. By keeping the condyle in the fossa, as we must, the only way the gonion can move posteriorly is for the molars to grow upward.

Fourth: In a post treatment growth study of 72 patients George Schudy pointed out this same relationship in 1973. He stated that, "Many of the differences between the high and low angle groups that were pointed out above are explainable in terms of the comparatively large horizontal condylar growth and the greater increase in the lower anterior facial height in the high angle group." What usually causes the increase in lower anterior facial height (in the post treatment period)? The vertical growth of the lower molars. It is comforting to find that all four approaches come up with the same answer and tend to confirm each other.

Thus, we have pointed out four studies which have confirmed the same relationship:

1. A 62 subject growth group and 50 subject treatment study,
2. A 95 random sample growth study,
3. An implant study by Bjork, and
4. A 72 patient post treatment study.

Everyone to their own opinion, but we think it is reasonable to believe that horizontal condylar growth is partially caused by vertical growth of the lower first molar. Then in turn horizontal condylar growth causes forward movement of the chin.

We have tried to comprehensively study horizontal condylar growth and point out its function in the growth of the jaws. It is hoped that this information will be a valuable addition to the total body of orthodontic knowledge.

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