The zygomatic air cell defect (ZACD) on panoramic radiographs.

@article{Tyndall1987TheZA,
  title={The zygomatic air cell defect (ZACD) on panoramic radiographs.},
  author={Donald Tyndall and Stephen R Matteson},
  journal={Oral surgery, oral medicine, and oral pathology},
  year={1987},
  volume={64 3},
  pages={373-6}
}