In the history of Orthodontics, so far as I know, we have never had a stable landmark from which to measure anteroposterior growth.

In 1997 in the "Schudy Chronicles" on the Internet, Fred Schudy proposed a vertical line drawn downward from sella turcica perpendicular to Frankfort, as a stable landmark for measuring anteroposterior growth. Schudy suggested the term "The great divide" for this stable line. Basion, articular and the glenoid fossa grow posteriorly from this line, and downward from sella and Frankfort.

In the past investigators have drawn a line downward from sella for various purposes, but not to divide the anatomical parts which grow anteriorly from those which grow posteriorly. To record the forward and downward movement of points on the profile, various authors have drawn a line from sella to these points on both the hard and soft tissue profiles. But such a line is a diagonal of a rectangle; when what we are really interested in is the length of the sides of this rectangle.

Since we now have a stable line from which to measure, we automatically have the two sides of the rectangle. We can now measure the craniofacial complex scientifically. The one millimeter grid used by Coben is an excellent method of measuring vertical and horizontal growth.

The "mechanism of growth concept" measures vertical and horizontal growth of the posterior aspect of the jaws. These measurements control the vertical and horizontal position of the chin and also control the rotation of the mandible. Controlling the moving parts of the face means controlling the function of the jaws.

In Article No. 11 of the "Schudy Chronicles" on the Internet, it was shown that basion grows downward with relation to Frankfort and sella, and grows posteriorly with relation to the great divide. This fact renders basion undesirable for registration in superimposition. Also, it was determined that foramen magnum can shrink in diameter as much as four or five millimeters from age 3 months to 16 years. This was a great surprise.

The forward growth of the maxilla seems to proceed independently, but in most instances quite harmoniously with that of the mandible; however, the maxillary teeth in many instances are driven forward by the growth of the mandible.

In summary, it has been shown that the horizontal growth of the craniofacial complex should be scientifically measured from the "great divide"-the vertical line which divides posteriorly growing anatomical parts from anteriorly growing parts.

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