T HE ability to correctly interpret dental and oral radiographs is an accomplishment which every dentist should possess. In fact, it should be viewed not only in the light of an accomplishment, but as a requisite of modern dentistry. It is to be acquired by practical experience which must have for its foundation, first, a thorough knowledge of the anatomy of the parts involved; second, a familiarity with the appearance in the radiograph of the dental and oral structures under normal conditions;

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... and, third, a knowledge of the pathological conditions which may develop in these structures, and the character of the anatomical changes which they bring about. We should keep in mind the fact that radiographs are shadow pictures, and that the effect produced by the x-ray upon the photographic plate is but a shadowgraphic representation of the tissues through which the rays have passed. As this ray penetrates all matter in inverse ratio to its mass or density, the shadow picture which is left upon the photographic plate is simply a record of the varying density of the tissues through which the rays have penetrated. The x-ray is particularly applicable to the dental and oral structures, owing to the fact that these structures di#er su$ciently in degree of density to permit of their appearing in a characteristic manner upon the photographic plate. For instance, it will be noted upon the examination of a dental radiograph, that metallic fillings, if they are present, appear as white masses, and root fillings as somewhat less white lines. The enamel and dentin are next in density, while root canals show plainly as dark channels in the dentin, and the alveolar process and maxillae show their fine uniform cancellous structure in various degrees of density depending .upon their thickness. Because the structures within the field of our specialty have a characteristic appearance under normal conditions, any alterations or change in these structures is at once evident upon the plate, thus affording us a means of studying intra vitam the gross pathology of the structures of the oral cavity.