Basing a Study On the Occlusal Plane
When a study is based on occlusal plane, it is hopelessly flawed right in the beginning. In the year 2000 four authors published an article based on the occlusal plane. Three of these authors had Ph.D. degrees after their names. When we base a study on invalid principles we have no chance of producing valid results.
The occlusal plane is not stable enough to be used as a basis for a study of the growth of the jaws, or as a basis for the analysis of treatment results. The occlusal plane is a result of growth, not a cause.
In Article 41, Figure 4 of the Schudy Chronicles is shown a comparison of superimposing on the occlusal plane and superimposing on sella horizontal and the great divide. The two methods are demonstrated on the same patient – the comparison is shocking. The nose is shown to grow forward 5 mm more when superimposing on the occlusal plane and the difference in the two methods increases in the lower face. Bjork advocated the use of the occlusal plane as a plane of reference and the profession, for 30 years, has blindly followed his recommendations. What has happened to independent thinking?
The occlusal plane changes its inclination any time there is a differential in the vertical growth of the anterior and posterior teeth. The occlusal plane changes its position with relation to the mandibular plane as the mandibular teeth grow vertically.
The occlusal plane changes its inclination with relation to the cranial base when there is a differential in the vertical growth of the maxillary posterior and anterior teeth. The occlusal plane changes its position when the maxillary teeth grow downward. Of course, the occlusal plane can both rotate and change its position at the same time. Thus, we see that the occlusal plane is dependent on the vertical growth of the teeth, and therefore is not adequate as a stable landmark for orientation. It is not an entity, but is a line where two entities meet.
It is hoped that most orthodontists will read this discourse in the near future and will desist from using the occlusal plane as a basis for studying the growth of the craniofacial complex.
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