Early in the "cephalometric era" there was much interest in the anatomical cause or anatomical basis for the forward position of the chin in the facial profile. With the advent of the science of cephalometrics, introduced by the invention of the cephalometric head holding mechanism by Dr. B. Holly Broadbent, Sr., came exciting possibilities for the study of anatomy of the human head.

This invention "jump started" a whole new era of anatomical study which is still going on. We owe Dr. B. Holly Broadbent a debt of gratitude for this wonderful invention. Dr. Holly Broadbent, Jr., custodian of the vast research records at Western Reserve University, is carefully preserving these valuable records.

From 1930 to 1950 only universities and research institutions had access to this cephalometric equipment; but in 1950 Dr. Herbert Margolis introduced head holding equipment which adapted the cephalometric radiogram to the private office. What a tremendous impetus this gave the field of Orthodontics!! What a tremendous contribution!!

Among the many research studies spawned by this new movement was a study of the face in profile by Dr. Arne Bjork in 1947. In this study Bjork attempted to find the anatomical cause of the position of the mandible in the craniofacial complex-what causes the anteroposterior location of the symphysis.

This investigation led Bjork to believe that the saddle angle, the joint angle, the jaw angle, the chin angle and corpus length would explain why the chin is so located in the craniofacial complex. Please see Fig. 1 (Bjork's diagram) and Fig. 2 (edentulous case). In this study Bjork selected the top and bottom ten percentiles for further study. He found that the ten percent with the chin farthest posteriorly had 9.32 mm more anterior vertical facial height.

Fig. 1: The facial diagram by Bjork to explain prognathism. Fig. 2: This is an illustration of an edentulous patient showing the relationship between the vertical and horizontal dimensions.

This was the most important measurement in the entire study, yet there was no attempt to evaluate it. This difference of 9.32 mm in anterior facial height was the cause of the marked difference in anteroposterior positions of the chins in the two percentiles. Thus, it becomes quite clear that the vertical dimension of the human face, caused by the vertical growth of the molar teeth, affects the anteroposterior position of the symphysis. This study was early in the "cephalometric era" and any incorrect interpretations can easily be forgiven.

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