Abstract
Previous studies have shown a relationship between mandibular positional changes in maximum jaw opening and craniofacial morphology. The purpose of this study was to evaluate the mandibular positional change in maximum opening with measurement of both incisor and condyle points, and to analyze the correlation between the positional change and the craniofacial morphology. The subjects were 125 untreated orthodontic patients (42 males and 83 females, mean age: 15.4 years) who have no history and presence of temporomandibular disorders. Lateral cephalograms were obtained from each subject in the intercuspal position and in the maximum opening position. Six variables of the positional change of the mandible and 54 cephalometric variables were measured by using a computerized cephalometric system. Methodological errors were 0.14mm in linear values and 0.27 degrees in angler values. To reduce the number of variables and to make use of existing correlations, factor analysis determined 3 factors for the positional change of the mandible were determined by factor analysis. Factor 1 (explaining 51.1% of variance), factor 2 (30.9%), and factor 3 (12.4%) could be defined as the posterior direction of incisor opening, the amount of condylar movement, and the amount of incisor movement, respectively. Significant correlations (p<0.01) were observed in factor 1 with GoGn/SN (r=0.44) and SNA (r=0.40), factor 2 with SE (r=0.57) and SN/NBa (r=0.47), and factor 3 with SNB (r=0.64), SL (r=0.67) and facial angle (r=0.57). These results suggested that opening direction of incisors and the amount of condylar movement as well as the amount of incisor movement should be considered when describing the mandiblar position in maximum opening, and that hyperdivergence of the face and maxillary retrognathism correlate with the opening direction of incisors, and the anteroposterior position of the temporomandibular joint correlates with the amount of condylar movement.
