573 INTRODUCTION When the qualities of dental roentgenograms are evaluated, some parameters are generally considered: a) the radiographic density or the optical density measure of the degree -of film darkening; b) the radiographic contrast or the capacity to sharply distinguish different tones of gray on the same roentgenogram; c) speed or the reciprocal of the exposure required to produce a density of 1.0 above base-plus-fog; d) resolution of the exposure settings available on the X-ray unit, which limits the density value obtained on the line-pair plate images (Fuchs, 1971). The comparison between radiographic densities seems to be an easy task to perform measuring the optical density at the darkest site of the roentgenogram with photodensitometer, but the density is measured by the ability of the developed silver in the piece of film to stop light from passing through. The darkest sites are always the areas where the X-rays reach the film directly (zero scale), with no obstacle interposed between the source of radiation and the surface of the film. On the other hand, the contrast is more complex. The contrast is critical for distinguishing objects in a radiographic film. Contrast in a dental x-ray image is influenced by three factors: subject contrast, film contrast and processing. In fact, when the radiographic contrast is studied, an aluminum penetrometer, it is commonly used to record the range of different tones of gray produced by the progressive thickness or height of the stepwedge aluminum penetrometer on the same exposed film, subject contrast (Manson-Hing and Bloxon, 1985). The scale of resultant gray tones, which may range from white to black on the radiograph is used to evaluate sharpness to distinguish several hues of gray, principally between adjacent steps of the penetrometer. When the contrast between roentgenograms are compared, many difficulties may arise, if one considers that the measures of the optical density at the radiographic bands (relative to the various steps of the penetrometer) are not mutually independent, when it is used a aluminum stepwedge, the decreasing thickness of the steps produces a multiplicative effect on the progressively darker hue of the images of the aluminum steps on the roentgenogram. This fact may cause considerable difficulty in the statistical analysis of the experimental results, and based in this concept, the present method was developed, to compare the diagnostic quality by means of the radiographic density and contrast using a single mathematics transformation of the original data of densities. Int. J. Morphol., 25(3):573-578, 2007. A Singular Method to Compare Dental Radiographic Films Used to Study Maxillofacial Structures Un Singular Método Comparativo de Radiografías Dentales Usadas en Estudios de Estructuras Maxilofaciales * Plauto Christopher Aranha Watanabe; ** João Paulo Mardegan Issa; * Luiz Carlos Pardini; * Solange Aparecida Caldeira Monteiro & * Alma Blásida Concepción Elizaur Benitez Catirse WATANABE, P. C. A.; ISSA, J. P. M.; PARDINI, L. C.; MONTEIRO, S. A. C. & CATIRSE, A. B. C. E. B. A singular method to compare dental radiographic films used to study maxillofacial strutures. Int. J. Morphol., 25(3):573-578, 2007. SUMMARY: The aim of this article is to present a singular and practical method to compare roentgenograms, concerning optical density and contrast. This method is specifically indicated for research related to stepwedge penetrometer and photodensitometer. KEYWORDS: Dental radiographic films; Radiographic density; Radiographic contrast. * Professor, Faculty of Dentistry of Ribeirão Preto, University of São Paulo, São Paulo, Brazil. ** Graduate student, Faculty of Dentistry of Ribeirão Preto, University of São Paulo, São Paulo, Brazil.