. Elementary and dental radiography / by Howard Riley Raper . the BenoistPenetrometer. Fig. 381. Kassett. The exact penetration of the X-rays can be de-termined accurately and easily by the use of theBenoist penetrometer. (Fig. 382.)Lay the penetrometer on the plate where it will be exposed whilethe exposure for the radiograph is being made. When the plate is de-veloped the radiograph of the penetrometer will appear as a circle ofvarying shades surrounding a circle or spot. The shade, counting fromthe darkest as number one, which matches the center or spot is the pene-tration of the tube on th
. Elementary and dental radiography / by Howard Riley Raper . the BenoistPenetrometer. Fig. 381. Kassett. The exact penetration of the X-rays can be de-termined accurately and easily by the use of theBenoist penetrometer. (Fig. 382.)Lay the penetrometer on the plate where it will be exposed whilethe exposure for the radiograph is being made. When the plate is de-veloped the radiograph of the penetrometer will appear as a circle ofvarying shades surrounding a circle or spot. The shade, counting fromthe darkest as number one, which matches the center or spot is the pene-tration of the tube on the Benoist scale. Very low vacuum tubes showing a penetration of only about two 346 APPENDIX will not give good radiographs of any part thicker than the hand, regard-less of the length of exposure. Before such a tube is used its vacuumshould be coaxed up by running a current of two or three milliamperesthrough it for a few minutes each Fig. 3S4A. Ketchan film-holder in posi-Fig. oS3. Small lead protection box for films. tion for lower third molar. Repeated and prolonged efforts to make radiographs with a tube,the vacuum of which is too low may result in producing an X-ray a tube gives 8 or 10 Benoist penetration it will probably notmake good radiographs. They will be lacking in contrast because theX-rays are so penetrating that they penetrate bone and soft parts made with a tube of such high penetration sometimes, besideslacking contrast and detail, will show a brown color from the glass sideof the negative. This brown color is indicative of what is called burn-ing up the emulsion with a too-high penetration. Figure 383 ilustrates a small lead box; insideSmall Eead BOX. dimensions about 5x6 inches, which is a most prac-tical one for small dental films. MAKING DEXTAL RADIOGRAPHS 347 Figure 384 illustrates the Ketcham film holders,the most elaborate set devised. Figure 384A i; aradiograph sho
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