ABSTRACT
In Orthodontic diagnosis and treatment planning one of the most important issue is an accurate anteroposterior measurement of jaw relationship. The most commonly used angular and linear measurements that have been proposed, such as ANB angle and Wit's appraisal can be inaccurate and misleading due to their dependence on various factors. This study was aimed at establishing a new cephalometric measurement, named the micro angle, to assess the sagittal jaw relationship with accuracy and reproducibility. The micro angle uses 3 skeletal landmarks, point A, point B and a perpendicular line from point A to the mandibular plan. One hundred and fifteen pretreatment cephalometric radiographs of orthodontic patients [mean age 16 +/- 2 years] were selected on the basic of inclusion criteria according to their skeletal and profile patterns. The patients compromised of 30 class I, 45 class II and 40 class III skeletal relationships and profile pattern, the mean and standard deviation for the new angel [micro] and the previous reported angle [beta] were evaluated. One way analysis of variance [ANOVA] and the Newman-Keuls test were used for data analysis as well as, dermination of the new angle's specifity and sensitivity comparing with beta angle. The results obtained showed that a patient with a micro angle between 16.1 degree and 23.9 degree can be considered to have a class I skeletal pattern. A more acute micro angle is an indication of a class II skeletal pattern and a more obtuse micro angle indicates a class III skeletal pattern. The new angle [micro angle] has an acceptable specificity and sensitivity in determining the anteroposterior relation of jaws and thus can be used for assessing the type and severity of jaw discrepancies, besides the other diagnostic parameters