Measurement and Interpretation of a Maxillary Occlusal Cant in the Frontal Plane

Abstract

A cant of the maxillary intermolar (M1-M1) plane is a reflection of facial asymmetry and can be measured on an anterior-posterior cephalogram in degrees relative to the true horizontal or directly on the patient as the difference in millimeters between the right and left medial canthi to canine distances. The purpose of this study is to measure the correlation between the maxillary cant measured in degrees and measured in millimeters. We hypothesize that the number of degrees of maxillary cant equals the millimeter difference between the lengths of the 2 sides of the maxilla, based upon the trigonometric relationship between the degree of cant, vertical length, and M1-M1 distance. To confirm this hypothesis, we evaluated a range of M1-M1 distances and computed the predicted vertical discrepancy between the 2 sides of the maxilla. Bivariate correlations were used to evaluate the association between the degree of cant and predicted vertical discrepancy. In the range of M1-M1 distances (47.5-61.1 mm) evaluated, cants ranging from 3 to 10 degrees are highly correlated with the vertical difference in millimeters (r = 0.96, P < .01). The mean error between the degree of cant and vertical difference was 9%. The degrees of occlusal cant relative to the true horizontal measured cephalometrically in the frontal plane is equal to the linear millimeter difference between the right and left medial canthi to the right and left canine tips.