Analysis of the phase differences between bilateral condylar movements using the cross power spectral density

Abstract

Purpose : To investigate the relationship between facial morphology differences and phase differences in bilateral condylar movements before and after orthognathic surgery. Methods : Total 14 subjects (5 male and 9 female, mean age: 21.9, range: 19-28) were selected, and CT data were collected before surgery and after surgery. All subject were undergone bilateral sagittal split ramus osteotomy in combination with Le Fort I osteotomy. Personalized splints were made for image registration and to track mandibular movement. The movements of the bilateral condyles were tracked and stored in terms of their CT coordinates using an optical tracking system. The CT images were reconstructed three-dimensionally and then normalized with the image parallel to the Frankfort horizontal plane (FH plane). The phase differences between bilateral condylar movements were calculated with the cross power spectral density. The calculated phase differences and facial morphologies were analyzed using Pearsons correlation coefficients. Results : Before surgery, the phase differences between bilateral condylar movements were randomly distributed regardless of the facial morphology. A patient who had severe asymmetry may have a short time delay and a patient who had relatively low asymmetry may have a long time delay. The correlation between the time delay and the morphology before surgery was not significant in the X, Y or Z directions (P>.05). After surgery, the relationship between the time delay and menton angle (MA) was statistically correlated in the Y and Z directions (P<.05). While CGM angle, GonMen, ConMen and ConGon parameters after surgery were not statistically significant, the correlation coefficient on the Z axis after surgery increased. Conclusion : Given that the phase differences and morphology differences were not correlated before surgery, the results of this study imply that the time delay may be related to other factors. These factors could be the inside characteristics of the temporomandibular joint or the degree of muscle asymmetry. Although the time delay after surgery was correlated with the MA morphology in the Y and Z directions, the evidence was weak due to the limited sample size. It is expected that this result will be clearer if future studies use data from more patients and other modalities such as MRI and EMG study.