Depiction and clarity of TMJ in corrected tomography: influence of variabilities of the pre-estimated condylar angle measurements

ABSTRACT

The primary objective of TMJ tomography is the accurate depiction of anatomic detail from which diagnostic information concerning osseous morphology, surface irregularities and condylar-fossa relationships can be determined. The current use of the term corrected lateral tomography implies that the parasagittal condyle position and image layer have been individually selected on the basis of condyle position in relation to reference plane as determined by submento-vertex radiographs. This study was designed to evaluate the effect of variation of horizontal condylar angulation on the diagnostic quality of the produced tomographic images. The horizontal condylar angle was measured on dry skull using cephalometric submento-vertex radiograph using a standardized technique. Corrected lateral tomograms were produced using the pre-determined horizontal condylar angle and by varying this angle +2, +4, +6 and +8 or -2, -4, -6, and -8 degrees. Qualitative analysis, include depiction and clarity, of condylar head and outline form and cortication of the joint temporal components and quantitative analysis, include geometric linear and angular measurements of the produced tomograms were carried out by the investigators. The results of this study showed that condylar slopes were well demarcated in all cut depths while the temporal components were presented well in the most medial cuts only. By increasing or decreasing the condylar angle, the most medial cuts showed the highest concordance with the predetermined angle followed by the central cuts, while the most lateral cut revealed the heighst variation and was markedly affected. With regards to joint space, Joint space measurements were not greatly affected by decreasing the angle except at the extreme (-8°) but it is affected prematurely on increasing the angle by [+4°].