2018 Volume 58 Issue 1 Pages 1-5
Objectives: In this study, we examined the relationship between the angle of elevation and artifacts on cone-beam computed tomography （CBCT） of the temporomandibular joint （TMJ） using the subtraction method. The scans were obtained using a hybrid unit for dental CBCT and panoramic radiography （hybrid CBCT）.
Methods: We used a model to simulate the head of the mandibular condyle and the glenoid fossa. The model was fixed to the hybrid CBCT scanner. First, it was set in the home position, in which the height of the deepest point of the glenoid fossa matched the height of the X-ray tube’s focal spot. Thus, the X-ray beam passed through the model in a horizontal direction （angle of elevation: 0°）. Then, CBCT images were taken with different incident angles of elevation to determine how this influenced the obtained images. The approximate angles of elevation at model heights of 0-60mm （relative to the home position） were: 0mm: 0°, 20mm: 3.5°, 40mm: 7.0°, and 60mm: 10.5°. We also calculated standard deviation （SD） values for subtraction images produced by comparing the 0° images with those obtained at other angles.
Results: As the angle of elevation increased, more image distortion arose （the greater the SD values of the subtraction images were）.
Conclusions: When TMJ images are obtained using a hybrid CBCT scanner, the target area of the TMJ should have a low angle of elevation. If the angle is ＞3.5°, image artifacts can appear.
