Difference In Radiopacity Research Articles

Selection of optimum kilovoltage for dental radiography.

The most commonly used dental x-ray machines are designed to operate at kilovoltage peaks ranging from 50 to 70. There are no investigations in the dental literature which prove that this range will produce dental films most suitable for diagnosis, and the recent recommendations by Fitzgerald (1) are for dental x-ray equipment capable of producing higher kilovoltages than are available at present. Medical radiologists are not limited by a narrow kilovoltage range in their equipment nor by lack of information concerning optimum values for specific body areas. They recognize that different kilovoltages are required for acceptable penetration and have experimentally tested high voltages in the production of diagnostic films (2–6). It appears that this type of information would be valuable also to dental radiologists. The purpose of this investigation was to test the applicability of the high-kilovoltage technic to dental radiography and to determine the optimum kilovoltage for production of dental radiographs that are capable of demonstrating both hard-and soft-tissue lesions with one exposure. The investigation involved the study of radiographic contrast, which is defined as the degree to which a film will demonstrate differences in radiopacity over a given range of structural density. Many authors have expressed a preference for a film giving “high contrast” (7–12). Such films are “brilliant” and have sharp distinctions between tissues of differing radiopacity. Slight differences in a single tissue are readily apparent. The question unanswered at present is what degree of contrast is necessary to produce a film of highest diagnostic value. The contrast should be such that variations in all important structures can be easily seen; soft tissues should be differentiated from fluids and tissue voids, while on the same film sound enamel must be distinguishable from dentine, carious enamel, and metallic restorations. This goal is not achieved at the present time. In order to obtain the extremes of the radiopacity range in the oral cavity, it is an accepted procedure to utilize double-packet films and develop one of the exposures less than full time. Any study of contrast involves radiographic density, since both qualities of dental film are affected by the three basic factors—the type of film, the developing technic, and the tube kilovoltage. In addition, density is influenced by target-film distance and milliampere seconds of exposure. A change in kilovoltage alone will make a difference in the contrast but will also cause the density to be unsatisfactory. In order to maintain constant density, the milliampere seconds of exposure must be adjusted to compensate for each new tube potential. All other factors, such as film processing, type of film, and target-film distance, must be kept constant in each experiment.