| spherical amalgam | An alloy for dental amalgam composed of spherical particles instead of filings. (05 Mar 2000) |
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| aberration, spherical | <optics> A lens defect whereby image forming rays of one colour, passing through the outer zones of a lens come to focus at a different distance from the lens than do those of more central rays. With a simple spherical (or plano-spherical) lens the outer rays always meet the axis closer to the lens than do more central rays and the lens is uncorrected or undercorrected. When the reverse is true the lens has been overcorrected. (05 Aug 1998) |
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| amalgam | <dentistry> A soft metal which results from an alloy of a metal with mercury. Commonly used as a silver-tin or copper alloy in dentistry for fillings. (08 Jan 1998) |
| amalgam carrier | An instrument used to transport triturated amalgam to a cavity preparation and to deposit it therein. (05 Mar 2000) |
| amalgam matrix | A device used during placement of the amalgam mass within a compound cavity preparation, facilitating proper condensation and contour thereof by providing a confining wall. (05 Mar 2000) |
| amalgam strip | A linen strip without abrasive used to smooth proximal contours of newly placed amalgam restorations. (05 Mar 2000) |
| amalgam tattoo | A bluish-black or gray macular lesion of the oral mucous membrane caused by accidental implantation of silver amalgam into the tissue during tooth restoration or extraction. (05 Mar 2000) |
| pin amalgam | An amalgam restoration held in place largely by small metal rods protruding from holes drilled into tooth structure. (05 Mar 2000) |
| spherical | Pertaining to, or shaped like, a sphere. (05 Mar 2000) |
| spherical aberration | <microscopy> A lens defect in which image forming rays passing through the outer zones of the lens focus at a distance from the principal plane, different from that of the rays passing through the centre of the lens. The aberration caused by (near-paraxial) monochromatic light rays or electron beams passing through different radii of a lens not coming to the same focus. (05 Aug 1998) |
| spherical form of occlusion | An arrangement of teeth which places their occlusal surfaces on the surface of an imaginary sphere (usually 8 inches in diameter) with its centre above the level of the teeth. See: Monson curve. (05 Mar 2000) |
| spherical lens | A lens in which all refracting surfaces are spherical. (05 Mar 2000) |
| spherical nucleus | Spinal nucleus of accessory nerve, a slender column of motor neurons extending longitudinally through the central part of the ventral horn of the upper five segments of the spinal cord, giving origin to the spinal part of the accessory nerve. Synonym: nucleus spinalis nervi accessorii, globosus nucleus. (05 Mar 2000) |
| spherical recess | A rounded depression on the inner wall of the vestibule of the labyrinth, lodging the sacculus. Synonym: recessus sphericus, fovea hemispherica, fovea spherica. (05 Mar 2000) |
| dental amalgam | <chemical, dentistry> An alloy used in restorative dentistry that contains mercury, silver, tin, copper, and possibly zinc. Chemical name: Dental materials and fillings, amalgams (12 Dec 1998) |