Effects of niobium filtration and constant potential on the sensitometric responses of dental radiographic films.

Two half-wave self-rectified dental X-ray units and two constant potential units were compared with respect to the sensitometric properties of D- and E-speed emulsions. The effects of additional niobium filtration on the half-wave beams were explored. Important differences between the responses of the two emulsions identified inadequacies in the International Standards method for determining film speed. The constant potential units gave values of speed within the range of the half-wave rectified units. Additional niobium caused an increase in the film speed produced by the half-wave units, especially in the case of the lower kilovoltage, less filtered beam. For all beam qualities investigated, the film speed was related to the half value layer. No specific effects of the constant potential supply, nor of the niobium filtration were identified. Film contrast was unrelated to beam quality, and differed in several respects between the two emulsions.