Dental Fluorosis : Chemistry and Biology
Tóm tắt
This review aims at discussing the pathogenesis of enamel fluorosis in relation to a putative linkage among ameloblastic activities, secreted enamel matrix proteins and multiple proteases, growing enamel crystals, and fluid composition, including calcium and fluoride ions. Fluoride is the most important caries-preventive agent in dentistry. In the last two decades, increasing fluoride exposure in various forms and vehicles is most likely the explanation for an increase in the prevalence of mild-to-moderate forms of dental fluorosis in many communities, not the least in those in which controlled water fluoridation has been established. The effects of fluoride on enamel formation causing dental fluorosis in man are cumulative, rather than requiring a specific threshold dose, depending on the total fluoride intake from all sources and the duration of fluoride exposure. Enamel mineralization is highly sensitive to free fluoride ions, which uniquely promote the hydrolysis of acidic precursors such as octacalcium phosphate and precipitation of fluoridated apatite crystals. Once fluoride is incorporated into enamel crystals, the ion likely affects the subsequent mineralization process by reducing the solubility of the mineral and thereby modulating the ionic composition in the fluid surrounding the mineral. In the light of evidence obtained in human and animal studies, it is now most likely that enamel hypomineralization in fluorotic teeth is due predominantly to the aberrant effects of excess fluoride on the rates at which matrix proteins break down and/or the rates at which the by-products from this degradation are withdrawn from the maturing enamel. Any interference with enamel matrix removal could yield retarding effects on the accompanying crystal growth through the maturation stages, resulting in different magnitudes of enamel porosity at the time of tooth eruption. Currently, there is no direct proof that fluoride at micromolar levels affects proliferation and differentiation of enamel organ cells. Fluoride does not seem to affect the production and secretion of enamel matrix proteins and proteases within the dose range causing dental fluorosis in man. Most likely, the fluoride uptake interferes, indirectly, with the protease activities by decreasing free Ca2+ concentration in the mineralizing milieu. The Ca2+-mediated regulation of protease activities is consistent with the in situ observations that (a) enzymatic cleavages of the amelogenins take place only at slow rates through the secretory phase with the limited calcium transport and that, (b) under normal amelogenesis, the amelogenin degradation appears to be accelerated during the transitional and early maturation stages with the increased calcium transport. Since the predominant cariostatic effect of fluoride is not due to its uptake by the enamel during tooth development, it is possible to obtain extensive caries reduction without a concomitant risk of dental fluorosis. Further efforts and research are needed to settle the currently uncertain issues, e.g., the incidence, prevalence, and causes of dental or skeletal fluorosis in relation to all sources of fluoride and the appropriate dose levels and timing of fluoride exposure for prevention and control of dental fluorosis and caries.
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Tài liệu tham khảo
Aoba T, Kawano K, Moreno EC (1990a). Molecular conformation of porcine amelogenins and its significance in protein-mineral interaction:1H-NMR photo-CIDNP study. J Biol Buccale 18:189–194.
Aoba T, Shimoda S, Akita H, Holmberg C, Taubman MA (1991). Anti-peptide antibodies reactive with epitopic domains of porcine amelogenins at the C-terminus. Arch Oral Biol 37:249–255.
Baelum V, Manji F, Fejerskov O (1986). Posteruptive tooth age and severity of dental fluorosis in Kenya. Scand J Dent Res 94:405–410.
Clarkson BH, Fejerskov O, Ekstrand J, Burt BA (1996). Rational use of fluorides in caries control. In: Fluoride in dentistry. Fejerskov O, Ekstrand J, Burt BA, editors. Copenhagen: Munksgaard, pp. 347-357.
Crenshaw MA, Bawden JW (1984). Proteolytic activity in embryonic secretory enamel. In: Proceedings, tooth enamel IV. May 24-27, 1984, Odawara, Japan. Fearnhead RW, Suga S, editors. Amsterdam: Elsevier, pp. 109-113.
Dean HT (1942). The investigation of physiological effects by the epidemiologic methods. In: Fluorine and dental health. Moulton FR, editor. Washington: American Association for the Advancement of Science, pp. 23-31.
Eastoe JE, Fejerskov O (1984). Composition of mature enamel proteins from fluorosed teeth. In: Proceedings, tooth enamel IV. May 24-27, 1984, Odawara, Japan. Fearnhead RW, Suga S, editors. Amsterdam: Elsevier, pp. 326-330.
Ekstrand J (1996). Fluoride metabolism. In: Fluoride in dentistry. Fejerskov O, Ekstrand J, Burt BA, editors. Copenhagen: Munksgaard, pp. 55-68.
Elliott JC (1994). Structure and chemistry of the apatites and other calcium orthophosphates. In: Studies in inorganic chemistry. Vol. 18. Amsterdam: Elsevier.
Fejerskov O, Baelum V (1998). Changes in prevalence and incidence of the major oral diseases. In: Oral biology at the turn of the century. Truth, misconcepts and challenges. Guggenheim B, Shapiro H, editors. Zürich: Karger, pp. 1-9.
Fejerskov O, Johnson NW, Silverstone LM (1974). The ultrastructure of fluorosed human dental enamel. Scand J Dent Res 82:357–372.
Fejerskov O, Thylstrup A, Larsen MJ (1977). Clinical and structural features and possible pathogenic mechanisms of dental fluorosis. Scand J Dent Res 85:510–534.
Fejerskov O, Manji F, Baelum V, Moller IJ (1988). Dental fluorosis. A handbook for health workers. Copenhagen: Munksgaard.
Fejerskov O, Yanagisawa T, Tohda H, Larsen MJ, Josephsen KAJ, Mosha H (1991). Posteruptive changes in human dental fluorosis—a histological and ultrastructural study. Proc Finn Dent Soc 87:607–619.
Fejerskov O, Richards A, DenBesten PK (1996). The effect of fluoride on tooth mineralization. In: Fluoride in dentistry. 2nd ed. Fejerskov O, Ekstrand J, Burt BA, editors. Copenhagen: Munksgaard, pp. 112-152.
Glass RL (1982). Secular changes in caries prevalence in two Massachusetts towns. J Dent Res 61(Spec Iss):1352–1355.
Hodge HC, Smith FA (1965). Fluoride chemistry. Chapter 4. Simons JH, editor. Orlando, FL: Academic Press.
Ishii T, Suckling G (1986). The appearance of tooth enamel in children ingesting water with a high fluoride content for a limited period during early tooth development. J Dent Res 65:947–977.
Jackson RD, Kelly SA, Katz B, Brizendine E, Stookey GK (1999). Dental fluorosis in children residing in communities with different water fluoride levels: 33-month follow-up. Pediatric Dent 21:248–254.
Josephsen K, Fejerskov O (1977). Ameloblast modulation in the maturation zone of the rat incisor enamel organ. A light and electron microscopy study. J Anat (Lond) 124:45–70.
Kierdorf U, Kierdorf H, Sedlacek F, Fejerskov O (1996). Structural changes in fluorosed dental enamel of red deer (Cervus elaphus L) from a region with severe environmental pollution by fluorides. J Anat 188:183–195.
Kleerekoper M, Mendlovic DB (1993). Sodium fluoride therapy of postmenopausal osteoporosis. Endocrine Rev 14:312–323.
Larsen MJ (1975). Enamel solubility caries and erosions (thesis). Aarhus: Royal Dental College.
Larsen MJ, Fejerskov O, Josephsen K, Hammarström L (1977). The action of acute doses of fluoride on serum calcium level in relation to dental hard tissue formation in rats. Calcif Tissue Res 22:454–457.
Marthaler TH (1990). Caries status in Europe and predictions of fluoride trends. Caries Res 24:387–396.
Moradian-Oldak J, Leung W, Tan J, Fincham AG (1998). Effect of apatite crystals on the activity of amelogenin degrading enzymes in vitro. Calcif Tissue Int 39:131–140.
Moreno EC, Kresak M, Hay DI (1978). Adsorption of two human parotid salivary macromolecules on hydroxy- fluorhydroxy- and fluorapatites. Arch Oral Biol 23:523–533.
Mura-Galelli MJ, Narusawa H, Shimada T, Iijima M, Aoba T (1992). Effects of fluoride on precipitation and hydrolysis of octacalcium phosphate in an experimental model simulating enamel mineralization during amelogenesis. Cells Mater 2:221–230.
Nikiforuk G, Simmons NS (1965). Purification and properties of enamel protein. J Dent Res 44:229–248.
Pindborg JJ (1982). Aetiology of developmental enamel defects not related to fluorosis. Int Dent J 32:123–134.
Robinson C (1997). Discussion for enamel fluorosis. Ciba Foundation Symp 205. Chichester: Wiley, p. 244.
Robinson C, Kirkham J, Brookes SJ, Bonass WA, Shore RC (1995). The chemistry of enamel development. Int J Dev Biol 39:145–152.
Russell AL (1963). The differential diagnosis of fluoride and nonfluoride opacities. J Public Health Dent 21:143–146.
Scheie AAa (1992). Dentifrices in the control of dental caries. In: Clinical and biological aspects of dentifrices. Embery G, Rølla G, editors. Oxford: Oxford University Press, pp. 29-40.
Schour I, Smith MC (1934). The histologic changes in the enamel and dentin of the rat incisor in acute and chronic experimental fluorosis. Univ AZ Tech Bull 52:6291.
Shimizu M, Fukae M (1983). Enamel proteins. In: Mechanisms of tooth enamel formation. Suga S, editor. Tokyo (Japan): Quintessence Publ., pp. 125-141.
Ten Cate JM, Featherstone JDB (1996). Physicochemical aspects of fluoride-enamel interactions. In: Fluoride in dentistry. Fejerskov O, Ekstrand J, Burt BA, editors. Copenhagen: Munksgaard, pp. 252-272.
Thylstrup A, Fejerskov O (1979). A scanning electron microscopic and microradiographic study of pits in fluorosed human enamel. Scand J Dent Res 87:105–114.
von der Fehr F, Schwarz E (1994). Recording dental caries and health statistics in Europe. In: Textbook of clinical cariology. Thylstrup A, Fejerskov O, editors. Copenhagen: Munksgaard, pp. 193-208.
Whitford GM (1989). The metabolism and toxicity of fluoride. Basel, Switzerland: Karger.
Whitford GM (1997). Determinants and mechanisms of enamel fluorosis. Ciba Foundation Symp 205. Chichester: Wiley, pp. 226–241.
Wright JT (1997). The protein composition of normal and developmentally defective enamel. Ciba Foundation Symp 205. Chichester: Wiley, pp. 85–99.
Yamazaki M, Sato K, Aoba T (2000). Mechanistic understanding of the maturation of developing enamel: plausible interactions among crystals, matrix proteins and proteases. Jpn J Oral Biol 43:60–71, 2001.
Yanagisawa T, Takuma S, Tohda H, Fejerskov O, Fearnhead RW (1989). High resolution electron microscopy of enamel crystals in cases of human dental fluorosis. J Electr Microsc 38:441–448.
Zeichner-David M, Diekwisch TGH, Fincham AG, Lau EC, MacDougall M, Moradian-Oldak J, et al. (1995). Control of ameloblast differentiation. Int J Dev Biol 39:69–72.