During the decades 1950 and 1960, Dr. Arne Bjork at the University of Copenhagen, Denmark, conducted some very important research pertaining to the growth of the jaws. He placed metal implants in the jaws of growing patients and took cephalometric radiograms over an extended period of time.

In 1972, Bjork et al published the results of these investigations in an article entitled "Facial Development and Tooth Eruption: An Implant Study at the Age of Puberty." This was published in the American Journal of Orthodontics, June 1972; 62:339-83.

This work was widely acclaimed and accepted worldwide. For twenty-four years no one has questioned its validity. However, in 1996, Fred Schudy, Houston, Texas, USA made an in-depth study of the article and reached the conclusion that the author had made an incorrect interpretation.

In February 1996 in an article entitled "Superimposition and Structural Analysis" published in the American Journal of Orthodontics, 109: 180-192, Schudy reported the results of his findings.

To date nobody seems to have an opinion one way or the other. Some orthodontists seem inclined to think that I am wrong, but there is one important question they cannot answer.

It is universally accepted that superimposition on S-N expresses the total anatomical change of the teeth and jaws both vertically and horizontally. Then any condylar growth shown by the implant studies must fit between the time two fossa and the time two gonion angle of the S-N superimposition. This is also universally agreed upon.

In analyzing the growth of the mandible in case number 14, Bjork removed it from the fossa and measured it completely out of anatomical context. He reports 20.4 mm of growth of the condyles. However, in the S-N superimposition the condyles grew only 11 mm (74 mm at time two and 63 mm at time one).

Thus the moot question is, how do you fit a 20.4 mm segment into a 10.5 mm slot? This is the question which nobody can answer. Unless the question can be answered satisfactorily, then Bjork made the wrong interpretation of his research.

If we were to use the 20.4 mm as the correct amount of condylar growth, this would extend the growth of the gonion angle downward 9.9 mm farther than it really did grow downward.

All rotation reported by the implant studies fitted nicely within the S-N superimposition from 10 to 16 years and was recorded when we made the time two tracing. Why will it not still fit within the S-N superimposition? The S-N superimposition reports 8^o of mandibular rotation and the implant superimposition reports 16^o rotation. Therefore, it would seem that the rotation was counted twice.

I hope that others will come forth with their opinion of the accuracy of the interpretation of the implant studies.

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