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Establishing the Normal Variation of Disk position of the TMJ in the Medio-Lateral Dimension using a New Coronal Imaging Plane at MRI

PI: Lars Hollender, D.D.S., Professor, Oral Medicine, School of Dentistry, University of Washington

In order to establish normal ranges for TMJ disk position, we will use MRI to study the position of the TMJ disk in young individuals without any clinical signs or symptoms or history of internal derangement or degenerative disease. The features of the bilaminar zone in sagittal MR images and the behavior of the bilaminar zone at jaw opening will be assessed. We will also examine intra- and inter-observer variation in classification of disk position in young healthy volunteers.

We have at this point been able to recruit all 40 subjects for this study. Although we have no definitive results at this point it is clear that the bilaminar zone is in contact with the articular fossa throughout the opening phase. These findings are in contrast to the currently held opinion, which has been based on findings at arthrography and dissection of the TMJ.

Although we have encountered individuals with disc displacements in our study it appears that the frequency is clearly less than has been reported in other studies of individuals without any symptoms or signs of internal derangement. As in other studies, we have also found individuals with disc displacement without reduction presenting with a perfectly normal range of motion upon opening and with no symptoms, signs or history indicating any likelihood of such a condition.

A few joints in our study exhibit a slightly forward position of the disc in the lateral parts of the joint, whereas there is a clearly normal position in other parts of the joint. Whether these cases ought to be considered normal or not has yet to be decided. We will utilize the information obtained from the oblique frontal views that were developed for the previous study and which offer unprecedented views of the articular disc. It seems that there is a striking congruence between the shape of the posterior border of the articular eminence and the shape of the disc in the normal cases. Whether or not this feature can be used for the diagnosis of the position of the articular disc is a question that will hopefully be answered by the continuing analysis of the data from the present study.

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