Additional Verification of the Validity of the Great Divide
It has now been approximately three years since the "Great Divide" was first discussed in the Schudy Chronicles on the Internet. We have been diligently trying to establish stable landmarks to which all anatomical points in the craniofacial complex can be accurately measured, both vertically and horizontally. It is most regrettable that after 65 years of cephalometrics, we are still trying to establish stable landmarks.
In Articles 1 and 24 we have shown objectively how and why the great divide divides posterior growth from anterior growth. In Art. 1, Fig. 1.5 we have shown that the skull grows concentrically around sella turcica. A 7 mm section of the circumference at age 3 months becomes a 14 mm section at age 16 years. Also we have shown why and how any diameter of the skull divides the direction of growth on each side of it. Since the great divide is a diameter of a circle representing the skull, then of course it does in fact divide anterior growth from posterior growth.
In the three years since the first discussion of this subject, there has been no response - neither for nor against, even though we have graciously invited the opinions of colleagues. (The silence is getting louder.) Thus, since the above is true, we have elected to try to point out additional objective evidence to verify and confirm this concept.
In studying the growth of a given individual, we have determined that basion moved 4 mm posteriorly with relation to sella turcica, and the upper first molar moved 6 mm anteriorly with relation to sella turcica. We have also determined that basion and upper first molar moved 10 mm apart. Then if we arbitrarily select another point to which we can relate growth, these increments may change for instance to 7 and 3, instead of 6 and 4, but the total must remain 10 mm.
We know that basion has moved 4 mm from its former position, and that the upper first molar has moved 6 mm from where it once was located - moving in opposite directions. Then when the increase in distance from the great divide (G.D.) to the upper first molar equals the actual distance that the tooth moved, and the distance from G.D. to basion equals the exact distance that basion moved, then this is proof that G.D. separates posterior from anterior growth.
If there were an anatomical structure immediately in front of the G.D., which could be accurately measured, it would be easy to establish the function of the G.D.; but as we move forward, the first structure which can be accurately measured is the first upper molar. There is a distance of approximately 20 to 30 mm which could be labeled "no man's land" since we have no way of accurately recording the growth of this area; however, we must postulate that growth in this area moves forward as does the maxillary complex.
The only anatomical structure which can be accurately measured horizontally in this area is the pterygomaxillary fissure. In a random sample of 95 subjects age 6 to 16, this fissure moved both posteriorly and anteriorly. While we are limited in the accurate measurement of the distance from the G.D. to the maxillary first molar, this in no way detracts from the accuracy of the G.D. as an accurate divider.
Let us, for the sake of illustration, say that there is not an exact line, but instead a narrow zone that divides anterior and posterior growth; but we would still need a line to represent the narrow zone. This additional verification lends further support to confirming the great divide.
Such diligent effort in the interest of establishing basic and necessary landmarks to accurately measure the craniofacial complex deserves either approval or rejection. I will expect a response to this important concept.
Return to the Index of Articles
Return to Dr. Schudy's Home Page
site design by web designs of houston
powered by triplecrown server at 
virtual servers for business on the web