Profile line accuracy in cephalometric radiographs

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.