Experimental Explanation of Maxillary Sinus Radiopacity as Seen by Waters' and Panoramic Projections

Clinical cases have been observed where a radiopacity has been found in the maxillary sinus on the Waters' view but does not correspond with that seen on a panoramic radiograph. In this paper the source of this disparity is demonstrated experimentally. Radiopaque material applied to the anterior wall of the maxillary sinus caused complete opacification of the sinus in the Waters' view, but only partial in the panoramic radiograph. When applied to the medial wall, only that surface was opaque in the Waters' projection compared to the entire sinus on the panoramic view. Only the lower half of the sinus was opacified on the Waters' view when the material was applied to the posterior wall but on the panoramic radiograph it was the lateral third. The apparent cause of this disparity in the radiographic findings between the Waters' and panoramic views is due primarily to the different projection angle of the central x-ray beam in relation to the maxillary sinus. Secondary images of other structures inherent in panoramic radiography further compound the disparity.