The effects of positioning variations in transcranial radiographs of the temporomandibular joint: a laboratory study.

The relationship of the mandibular condyle to the articular fossa and eminence as seen on transcranial oblique lateral (TOL) radiographs of the temporomandibular joint is used by some clinicians as an important diagnostic sign and indicator of treatment. The literature is divided on the validity of this. The aim of this study was to consider the effects of variations in both the position of the joint and the X-ray beam orientation on the image seen on TOL radiographs. TOL radiography of a mounted block specimen of a human temporomandibular joint and associated tissues was carried out using a range of specimen rotations (+20 degrees to -20 degrees with respect to the sagittal plane) and X-ray beam angulations (20 degrees, 25 degrees, 30 degrees). Analysis of tracings of the joint images showed that most of the parameters measured varied by statistically significant amounts with changes in either specimen rotation or beam angulation. It is concluded that any convention which purports to evaluate the position of the mandibular condyle in relation to the articular fossa from TOL radiographs is invalid when the orientation of the condyle to coronal and horizontal planes is unknown.