X-Ray-Induced Light Emission from Enamel, Bone, and Other Calcium Phosphate Materials

Early studies of fluorescence and phosphorescence of teeth (light emission during, but <10-8 seconds after cessation of, excitation and emission beyond 10-8 seconds after excitation is extinguished, respectively) involve macroscopic and microscopic technics, using ultraviolet light (UV) as a source of excitation.' Early studies and subsequent investigations of dental hard tissues using UV excitation indicate that the light emission was from the organic matrix.2-7 Also, X rays have been used to produce light emission from powdered amino acids and trypsin.8 Research begun as early as 1897 by Nichols and others9-1" laid much of the groundwork for fluorochemistry (i.e., the theory of luminescence, which deals with both phosphorescence and fluorescence). In many of these studies, the materials were crystalline solids, often of mineral origin, and UV, X-ray or electron excitation was used. Although phosphorescence and fluorescence of apatitic compounds are not widely mentioned in the literature, fluorochlorapatite is used for fluorescent lamp phosphors.'2'3 Bachman and Ellis'4 describe the visible fluorescence of bone under UV excitation of 3,650A UV light.14 Their preliminary experiments, however, indicate that bone does not fluoresce when excited by X rays in the energy range of 100kv. down to 20kv. The literature cited indicates that organic constituents of bones and teeth may be excited by UV or X rays and that impurityactivated synthetic apatites will fluoresce under UV excitation. Little attention, however, has been given to the inorganic crystal