Linear evaluation of the development of sagittal jaw relationship.

In cephalometrics both angular and linear variables have been proposed in the analysis of sagittal jaw relationship and jaw position. Angular measurements can be erroneous as a result of changes in facial height, jaw inclination, and total jaw prognathism; linear variables can be affected by the inclination of the reference line. In the present article, a method of geometric correction of linear analysis of sagittal jaw relationship and jaw prognathism (based on a standardized occlusal plane) is described. The method is applied to radiographic material (from King's College Hospital, London) of 33 children who, at the age of 19, exhibited Class I occlusal patterns. While uncorrected linear measurement suggested stability of the sagittal jaw relationship from the age of 11 to 19 years, the geometrically corrected value demonstrated a marked reduction in sagittal jaw relationship. The method is developed further to demonstrate the increase in jaw prognathism measured as lined parameters with origin at point sella, the results illustrating again the advisability of correction of geometric errors.