Discriminative thresholds of cephalometric indexes in the subjective evaluation of facial asymmetry

Introduction The purpose of this study was to determine the means and the ranges of the thresholds of cephalometric indexes by which orthodontists subjectively differentiate patients needing treatment for facial asymmetry from those who do not. The study was performed at the Departments of Orthodontics and Oral and Maxillofacial Radiology, Aichi-Gakuin University School of Dentistry in Nagoya, Japan, in 2004. Methods Ten orthodontists subjectively evaluated the frontal photographs of 100 subjects and classified them into 2 groups. The subjects in group A showed good or clinically acceptable levels of asymmetry and did not require treatment. Those in group B showed marked asymmetry, and treatment was recommended. The frontal cephalographs were also analyzed with 5 indexes related to the mandible. For each orthodontist, the threshold was determined by means of the discriminant analysis. Results As the number of subjects who were judged to require treatment increased, the threshold of cephalometric indexes became smaller, and the discriminant accuracy was reduced. Among the 5 indexes evaluated, the distance of menton (mean, 4.28 mm), maxillomandibular midline angle (mean, 4.31°), and the distance of L1 (mean, 2.78 mm) showed relatively high accuracy in all observers. Conclusions The distance of menton, the maxillomandibular midline angle, and the distance of L1 appeared to be relevant indexes for the subjective evaluation of facial asymmetry. The thresholds determined in this study could contribute to the planning and evaluation of orthodontic treatments.