screen (skren)

1. A sheet of any substance used to shield an object from any influence, such as heat, light, x-rays, etc. 2. A sheet upon which an image is projected. 3. Formerly, to make a fluoroscopic examination. 4. In psychoanalysis, concealment, as one image or memory concealing another. See also screen memory. 5. To examine, evaluate; to process a group to select or separate certain individuals from it. 6. A thin layer of crystals that converts x-rays to light photons to expose film; used in a cassette to produce radiographic images on film. [Fr. écran]
Bjerrum s.tangent s
s.-film contactthe closeness and uniformity with which the x-ray film in a cassette lies against the s. (6). Image resolution is dependent on this closeness and uniformity of s.
fluorescent s.a s. coated with fluorescent crystals such as the calcium tungstate used in the fluoroscope.
Hess s.a s. used in the measurement of ocular deviation.
intensifying s.a s. (6) used in radiography.
rare-earth intensifying s. (6) made of a rare-earth oxide phosphor, more efficient than calcium tungstate, especially at the higher kilovoltages used in modern radiography.
tangent s.a flat, usually black surface used to measure the central 30 degrees of the field of vision.Bjerrum s;
vestibular s.a s. made of acrylic resin that covers the labial or buccal surfaces of one or both dental arches; used to treat oral habits and to stimulate tooth movement by using perioral muscle force.


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