. Elementary and dental radiography . the plate or him. This ink must, I think, contain some salt of lead orbismuth, for the X-Rays penetrate it very poorly, and consequently thereis a shadow cast on the negative. I\Iy objections to marking small dental films in this manner is thatoccasionally the shadow of the markings will occur in such a place in theradiograph as to spoil the picture. The older methods of placing wiresbent to form the figures or letters for marking, or a stencil of sheet metal,between the source of rays and the plate, is highly unsatisfactory, so faras their application to
. Elementary and dental radiography . the plate or him. This ink must, I think, contain some salt of lead orbismuth, for the X-Rays penetrate it very poorly, and consequently thereis a shadow cast on the negative. I\Iy objections to marking small dental films in this manner is thatoccasionally the shadow of the markings will occur in such a place in theradiograph as to spoil the picture. The older methods of placing wiresbent to form the figures or letters for marking, or a stencil of sheet metal,between the source of rays and the plate, is highly unsatisfactory, so faras their application to the marking of small dental radiographs is con- M^ DENTAL RADIOGRAPHY cerned. After the negative is made, markings may be scratched in thefihn. But, as I said before, no system of marking the negative itself isas satisfactory as marking the envelope in which it is kept. One of the most unfortunate limitations of the Perspective. radiograph is that it lacks perspective. For example, though we are able to observe the exact mesio-distal. Fig. 125. (Reduced one-half.) position of an impacted tooth, we are unable to determine its bucco- orlabio-lingual position, with any degree of accuracy. The closer the object, which is being radiographed, is to the filmduring exposure, the clearer the resulting shadow will be. Thus, forexample, if an impacted cuspid lay lingually to the other teeth, and thefilm were held inside the mouth as usual, the detail in the picture of thecuspid would be a little greater than the detail in the other teeth. If thecuspid lay to the labial,—farther away from the film,—detail in it wouldbe less than in the other teeth. But, on the whole, this method of deter-mining bucco- or labio-hngual location is unreliable. READING RADIOGRAPHS 143 While I agree with Dr. C. H. Abbot, of Berlin, who has done somewriting and experimental work to prove that radiographs are not totallylacking in perspective, yet I do declare, from the standpoint of their prac-tical applicat
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