Accuracy of CBCT in Evaluating TMJ Spaces

OBJECTIVE: The purpose of this study is to determine the accuracy and the ability of Cone-Beam Computed Tomography (CBCT) to evaluate TMJ space in dry skulls.

METHODS: TMJ spacing was considered the distance between the condylar head of the mandibular and the articular eminence of the temporal. Twenty-six TMJs (thirteen dry skulls) were imaged using a CBCT machine (NewTom-3G, Aperio). A laser scanner (LS) mounted on an arm (Faro Arm, Faro Technologies Inc.) capable of measuring a surface at a precision of 25 microns was used as the gold standard to determine the precision of the CBCT data. The CBCT volume data was exported via the DICOM format and processed by an iso-surface segmentor using open source software (ParaView, Sandia National Laboratory). The resulting surface was reduced in size and saved in a polygonal format. Using polygon processing software (Rapidform2006, Inus Technology) the data from the laser scanner was registered with the polygonal model of the CBCT using reference targets composed of small titanium spheres to avoid x-ray scattering. Sphere models were then robustly fitted in both of the datasets using outlier detection and registered. This resulting registration was then used to quantify the difference between the polygons from both datasets.

RESULTS: An average difference of 0.012 mm with a two sigma variance of 0.4 mm was observed. There were no systematic biases observed.

CONCLUSIONS: Although a difference between CBCT and LS measurements were identified; CBCT appears to be sufficiently accurate to be used as a clinical tool to quantify TMJ space. Consideration has to be taken here with the fact that a dry skull study does not fully represent real life conditions. Due to the decreased radiation dose and speed of image acquisition CBCT imaging appears as to be a promising tool to advance current TMJ diagnostic standards.