The Position of Anatomical Porion in Different Skeletal Relationships

Previous research has shown that the position of glenoid fossa differs in different skeletal relationships. However, it is hard to identify and trace the glenoid fossa on a lateral cephalometric radiograph. The aim of the present study was to evaluate the anteroposterior and the vertical positions of the porion point (P) in different skeletal relationships as seen on lateral cephalometric radiographs. Methods: Two hundred eighty lateral cephalometric radiographs of orthodontic male patients (age range: 12 + 0.6) having different skeletal relationships were traced and corrected for magnification distortion. They were divided into three groups according to their sagittal relationships. All selected patients had average lower face height and mesofacial type. Five vertical and horizontal linear measurements were performed; from P to CF point [Ricketts], basion (Ba) and to condylion (Co). Intra and inter-examiner reliability tests were performed. Data were statistically analyzed using ANOVA test. Results: In relation to CF, P was significantly positioned more posteriorly in Class II than in Class I (P<0.05) or in Class III (P<0.05), and no statistically significant difference in the position of P between skeletal Class I and III relationships. In relation to Ba, P was significantly positioned more posteriorly in Class II than in Class I (P<0.05) and no statistically significant difference in the vertical or anteroposterior positions of P between skeletal Class I and III relationships. However, skeletal Class II subjects showed more superiorly positioned P than in Class III subjects when related to Ba (P<0.05). There was no statistically significant difference in the vertical and the anteroposterior position of the P to Co between different skeletal relationships. Conclusion: The position of porion (P) point on a cephalometric radiograph varies among different skeletal relationships. The posteriorly positioned P point in Class II subjects could be a cause for the mandibular retrognathism in skeletal Class II malocclusion * Lecturer of Orthodontics, Faculty of Dentistry Tanta University, Egypt Currently is Assistant Professor of Orthodontics, Faculty of Dentistry, King Abdul Aziz University, Jeddah, Saudi Arabia. ** Assistant Professor of Orthodontics and Chairman of Preventive Dental Sciences Department, King Abdul Aziz University, Jeddah, Saudi Arabia. Introduction: Assessment of anteroposterior position of the glenoid fossa was first reported by Wylie (1947) in an assessment of anteroposterior dysplasia. However, he used the posterior surface of the head of the condyle (calling it glenoid fossa). This assumption has a shortcoming of the fact that the head of the condyle can not represent the glenoid fossa in the sense that the condyle position can vary in relation to the glenoid fossa with variation of the position of the mandible. Ricketts (1957) reported that, theoretically at least, since the glenoid fossa is located in the general proximity of the middle cranial fossa, its relation to basion is presumed to remain relatively fixed. Bjork (1955) , on the other hand, disagreed with the importance of this relationship. Previous studies have indicated that the condylar position during orthodontic treatment of Class II malocclusions remained the same in about 60% of the cases. However, Ricketts studies were based on laminagraphs that are not currently available in most orthodontic practices. Schudy (1965) 4 reported that the dorsal migration of the glenoid fossa is a very real factor in many cases and tends to cancel out the growth of the condyles; thus, in a sense it is arrayed on the side of vertical growth. Previous research has shown that the position of glenoid fossa differs in different skeletal relationships. However, it is hard to identify and trace the glenoid fossa on a lateral cephalometric radiograph (Kantomaa , 1984; Pirttiniemi et al., 1991). So, other investigators (Agronin and Kokich, 1987) 7 used articulare (Ar) point as a reference for the glenoid fossa. This point, however, is known to be a non-anatomical point; rather, it is a