Exposure times at which dental xeroradiographs and radiographs have comparable optical density

Xeroradiographs and conventional radiographs were made of a dentulous human cadaver maxilla that was still covered with soft tissue. The times of exposure for the xeroradiographs started at 6 impulses (1 impulse = 1/60 second) and were increased by increments of 3 impulses through 48 for subsequent images, while the radiographs were made with D-speed film and exposure times of from 21 through 63 impulses, again at every third reading. The same x-ray machine, operated at 70 kVp and 15 mA, was used as the source of radiation for all images. Film/cassette-to-jaw relationship and focal-spot-to-film/cassette distance were standardized. Transmission optical density of the resulting images was determined. The results showed that radiographs with transmission optical densities comparable to those of xeroradiographs could be produced with exposure times approximately 3 times those used for xeroradiographs in the lower part of the range observed. This factor decreased to approximately 1.3 as optical density increased.