The determination of free-way space in edentulous patients: a cephalometric approach.

This study was prompted by the hypothesis that the contractile power of the masseter and medial pterygoid muscles influences not only the shape of the gonial angle of the mandible into which these muscles insert, but also that they play a major part in determining the amount of free-way space present in any individual. Tracings were made from the lateral cephalograms of 130 dentate subjects and the gonial angle measured in each case. Free-way space was also measured, using a dakometer, and the paired values subjected to statistical analysis. A strong inverse correlation was found to exist, indicating that throughout the sample a decrease (or sharpening) of the gonial angle is accompanied by a predictable increase in the free-way space. By applying the processes of linear regression to the paired results, a formula was obtained which may be used to predict the best value of one variable for any given value of the other. Thus, in an edentulous case, where the value of the free-way space measurement is unknown, a method is provided for predicting its best value by the determination of the patient's gonial angle through cephalometric analysis.