Profile line accuracy in cephalometric radiographs.

Abstract

Introduction: This study investigates the accuracy of facial soft-tissue profile lines in lateral cephalometric radiographs by comparing them to true profile lines derived from 3-dimensional photographs.

Methods: This prospective methodological study was performed on preexisting records of 100 orthodontic patients. The true profiles were obtained by defining the true midsagittal plane through best-fit approximation of mirrored 3-dimensional surface models. Two curves were drawn on each profile image, and landmarks and sliding semilandmarks were placed on them. This resulted in 2 profile landmark configurations per patient, which were superimposed using Procrustes superimposition. The Procrustes distances between corresponding landmarks were used as a metric to assess the accuracy of the cephalometric profile line, as compared with the true reference.

Results: On average, there were small statistically significant differences between the cephalometric and the actual profile lines (100,000 permutations; P = 0.031; median interlandmark distance, 0.84 mm). However, when assessing individual patients, the cephalometric profile line deviated significantly from the true profile, with 40% of the distances between corresponding landmarks being >1 mm and 10% being >2 mm. There were no differences between the sexes or between younger and older patients (aged 8.0-12.5 vs 12.5-55.0 years). However, there were small differences between 2 x-ray devices (median, 0.18 mm; P <0.001), which often exceeded 1 mm at the soft-tissue nasion area, probably because of the cephalostat.

Conclusions: On average, the lateral cephalometric radiographs might provide an adequate representation of the facial profile, but when individual patients are considered, there is often a clinically significant error. Thus, lateral cephalograms should be used with caution to evaluate the facial soft-tissue profile.