Mandibular Size and Position in 8-13 Year Old Iranian Children with Class II Division 1 Malocclusion

Statement of Problem: Assessment of mandibular size and position is essential when planning a treatment strategy for patients with Class II malocclusion. Purpose: This study was carried out to evaluate the mandibular size and position of 8- 13 year-old children with Class II Division 1 malocclusion whom were referred to the Faculty of Dentistry, Shiraz University of Medical Sciences, Iran. Materials and Methods: 935 lateral cephalograms of children with normal occlusion (425 films) and Class II Division 1 patients (510 films) referred to the Department of Orthodontics, School of Dentistry, Shiraz University of Medical Sciences, during 2002 to 2004 were evaluated. The control and Class II Division 1 subjects were each divided into three groups according to age (8-9, 10-11 and 12-13 years), and were further divided into two subgroups according to gender. The radiographs were converted to computer-readable X and Y coordinate and data obtained from 29 linear and angular measurements in the cranial base, mandible and dentition, were compared. Results: The cranial base angle was significantly larger in Class II Division 1 patients as compared to the control subjects. A smaller mandible along with a protrusive dentition was observed in the test group. The form and position of the mandible was also different in comparison to normal cases. All class II patients showed a vertical growth pattern and an increased facial height. Conclusion: The main factors responsible for class II Division 1 malocclusion in 8-13 year-old children in present study were retropositioning of the lower jaw and a short mandibular length.