Cephalometric Investigation of Class III Malocclusion According to McNamara Method

Abstract

Lateral teleradiography represents an indispensable paraclinical investigation in dento-maxillary anomalies. McNamara’s cephalometric analysis method is one of the most suitable in this case. The purpose of this study was to identify the most informative parameters according to McNamara method, that are specific for Class III malocclusion. The study sample consists of 6 lateral cephalometric radiograms that were examined according to principles described by McNamara. After cephalometric evaluation we detected a range of modifications characteristic for Class III. The mandible is positioned more antero-inferior than the normal values suggested by McNamara, which is confirmed by an average deviation of 6.7mm of the index Pg-Nasion perpendicular. There was detected a significant antero-posterior skeletal disharmony, proven by increased values (15.6mm) of the variable maxillomandibular difference. The maxilla has a retropositioned location compared to the cranial base expressed by the parameter A-Nasion perpendicular that is deviated 4.2mm posterior from the position considered normal. The goniac angle is more obtuse than the standard values. The increased value (+3.2°) of the angle between Frankfurt and mandibular plane confirms this modification. Mandibular length was excessive for all the patients with a medium exceed of the normal values of 13.1mm. As a result of this research we determined that t he most important informative value in class III diagnosis is possessed by the following parameters: the mandibular and maxillary length, maxillomandibular difference, the relation between the mandible and cranial base and the goniac angle value.