A new approach of assessing sagittal discrepancies: the Beta angle

Abstract

An accurate anteroposterior measurement of jaw relationships is critically important in orthodontic diagnosis and treatment planning. The angular and linear measurements that have been proposed can be inaccurate because they depend on various factors. The purpose of this study was to establish a new cephalometric measurement, named the Beta angle, to assess the sagittal jaw relationship with accuracy and reproducibility. This angle uses 3 skeletal landmarks-point A, point B, and the apparent axis of the condyle-to measure an angle that indicates the severity and the type of skeletal dysplasia in the sagittal dimension. Seventy-six pretreatment cephalometric radiographs of white patients were selected on the basis of 4 criteria that indicate a normal Class I skeletal pattern; the mean and the SD for the Beta angle were calculated. This group was compared with Class II and Class III skeletal pattern groups. After using the 1-way analysis of variance and the Newman-Keuls test and running receiver-operating-characteristics curves, we obtained results that showed that a patient with a Beta angle between 27 degrees and 35 degrees can be considered to have a Class I skeletal pattern. A more acute Beta angle indicates a Class II skeletal pattern, and a more obtuse Beta angle indicates a Class III skeletal pattern.