A Discussion of an Article by
Doctors Naumann, Behrents and BuschangThe title of the article was, "Vertical Components of Overbite Change: A Mathematical Model," and was published in the AJODO in the April 2000 issue.
Since one cannot discuss "vertical components of overbite change" without discussing the vertical growth of the molar teeth, which is the cause of overbite change, then the authors’ discussion has a very serious shortcoming.
Let me say that to base an analysis on the occlusal plane will lead to invalid concepts. The occlusal plane is an effect, not a cause. (So far the orthodontic profession has failed to accept the principle of "cause and effect.") A manuscript on the subject of "cause and effect" has been rejected by six different reviewers.
Björk and Skieller referred to the RL line (the occlusal plane) as defined by time one head film, and stated, "It could be compared to an implant line. Its changes during the different examination periods show what Björk and Skieller called "total mandibular rotation," which is the true jaw bone rotation not masked by remodeling processes at the lower border of the mandibular corpus."
In other words, Björk stated that the occlusal plane represented the true jaw bone of the mandible. Thus, Pancherz and his co-workers felt justified in using the occlusal plane as a basis for orientation.
In the Internet Article No. 42, entitled "The Translation of the Mandible," Figure No. 4, it has been shown that basing an analysis on the occlusal plane is alarmingly misleading. The fact that the occlusal plane is itself an effect, not a cause, makes it unreliable as a basis for orientation. Its position and inclination depend on the causative growth increments – on the relationship between vertical and horizontal growth. Please see Article No. 2 of the Schudy Chronicles.
In October 1967 I was asked to comment on a thesis by a graduate student, on the subject, "The Occlusal Plane as a Plane of Reference." The following is an excerpt from my reply:
"When I first began to study the occlusal plane I too used it was a reference plane for superimposition. In fact, I studied it rather extensively before discarding it. When one publishes articles on the occlusal plane as I have done, one must first study it comprehensively. You know when the ol’ neck is out it is subject to the axe."
"I would say that your study has a fundamental weakness. It is predicated on a very narrow premise. You selected only cases in which the occlusal plane did not change with relation to SN. The majority of growing individuals do not conform to this pattern."
"By using the occlusal plane as a reference, we are in effect using the terminal positions of the teeth to relate the bases from which the teeth grew. To me this is completely backward. If we want to know how much these teeth have grown from their bases why not just plain measure them in millimeters as I have done. Measuring individual increments, which are meaningful, and relating them to each other in the same individual has much importance from the standpoint of Orthodontic treatment and useful biological concepts."
"You state (p.33) that, "The direction and rate of growth is always expressed from a reference source". I have related increments to each other and not to reference planes. This is what nature does in an obscure cause-and-effect relationship. When we measure increments in this way they are unencumbered by reference planes and can be assigned their rightful contribution to the unfolding of the face."
When an investigator begins a study using the wrong premise, then it is impossible to compensate with sophisticated analyses and technology. For instance, the "mandibular skeletal changes" are caused by the rotation of the mandible. The investigator must first understand the effects of the rotation of the mandible. To analyze the vertical development of the jaws and ignore the vertical growth of the posterior teeth, is an impossibility.
Since the authors of the article under discussion based their analysis on the occlusal plane, their findings cannot possibly be valid.
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