Cephalometrics and facial shape: new thresholds by an overall approach to classic standards

Pretreatment lateral skull radiographs were studied to analyze the characteristics of facial morphology. Standard cephalometric measurements were compared with those provided by a Fourier description of the overall morphology. Skull patterns were divided into hyperdivergent, neutral, and hypodivergent groups (1) according to the standard thresholds of facial height ratio and (2) according to the mathematical distance between their Fourier coefficients and the Fourier coefficients of three reference plots. Linear regression analysis showed that all the Fourier variables were significantly correlated. The standard thresholds of normality used to classify patients as normal, hyperdivergent, or hypodivergent did not correlate with each other. Fourier analysis resulted in new thresholds of normality that are more accurate than previous norms developed by standard cephalometric measurements. These new thresholds take into account the overall morphologic characteristics of the patient and each separate measurement is strictly correlated with the others.