The chemical changes which occur during the process of carious destruction of enamel are complex due to a number of factors. First, substituted hydroxyapatite, the main component of dental enamel, can behave in a very complex manner during dissolution. This is due not only to its ability to accept substituent ions but also to the wide range of calcium phosphate species which can form following dissolution. In addition, the composition, i.e., the extent of substitution, changes throughout enamel in the direction of carious attack, i.e., from surface to interior. Both surface and positively birefringent zones of the lesion clearly illustrate that carious destruction is not simple dissolution. Selective dissolution of soluble minerals occurs, and there is the probability of reprecipitation. The role of fluoride here is crucial in that not only does it protect enamel per se but also its presence in solution means that rather insoluble fluoridated species can form very easily, encouraging redeposition. The role of organic material clearly needs further investigation, but there is the real possibility of both inhibition of repair and facilitation of redeposition. For the future, delivering fluoride deep into the lesion would appear to offer the prospect of improved repair. This would entail a delivery vehicle which solved the problem of fluoride uptake by apatite at the tooth surface. Elucidation of the role of organic material may also reveal putative mechanisms for encouraging repair and/or protecting the enamel mineral
References
1.
Anderson P., Elliott JC (1987). Coupled diffusion as basis for subsurface demineralisation in dental caries. Caries Res21: 522-525.
2.
Angmar B., Carlstrom D., Glas JE ( 1963). Studies on the ultrastructure of dental enamel. IV. The mineralisation of normal human enamel. J Ultrastruct Res8:12-23.
3.
Arends J., Davidson CL( 1975). HPO42- content in enamel and artificial carious lesions. Calcif Tissue Res18:931-941.
4.
Arends J., ten Cate JM (1981). Tooth enamel remineralisation. J Cryst Growth53:135-147.
5.
Borggreven JMPM, van Dijk JWE, Driessens FCM (1981). Effect of mono- and di-valent ions in diffusion and binding in tooth enamel. Arch Oral Biol26:663-669.
6.
Boyde A. (1989). Enamel. In: Handbook of microscopic anatomy. Oksche A, Vollrath L, editors. Berlin: Springer Verlag, pp. 309-473.
7.
Brown WE, Patel PR, Chow LC ( 1975). Formation of CaHP04.H20 from enamel mineral and its relationship to caries mechanism. J Dent Res54:475-481.
8.
Burke EJ, Moreno EC (1975). Diffusion fluxes of tritiated water across human enamel membranes. Arch Oral Biol20:327-332.
9.
Chow LC, Takagi S. (1989). A quasi-constant composition method for studying the formation of artificial caries-like lesions. Caries Res23:129-134.
10.
Christoffersen J., Christoffersen MR, Kibalczyc W., Perdok WG (1988). Kinetics of dissolution and growth of calcium fluoride and effects of phosphate in solution and incorporated in the crystals on these processes. Acta Odontol Scand36:325-326.
11.
Daculsi G., Kerebel B. (1977). Some ultrastructural aspects of biological apatite and possible role of dislocations. J Biol Buccale5:203-218.
12.
Darling AI (1956). Studies of the early lesion of enamel caries with transmitted light, polarised light and radiography. Br Dent J101:289-297.
13.
Darling AI (1961). The selective attack of caries on the dental enamel. Ann R Coll Surg Engl29:354-369.
14.
Driessens FCM, Verbeek RMH (1982). The probable phase composition of the mineral in sound enamel and dentine. Bull Soc Chim Belg91:573-596.
15.
Driessens FCM, Verbeek RMH (1985). Dolomite as a possible magnesium containing phase in human tooth enamel. Calcif Tissue Int37:376-380.
16.
Elliott JC (1997). Structure, crystal chemistry and density of enamel apatites. In: Dental enamel. Winter GB, Chadwick DJ, Cardew G, editors. CIBA Foundation Symposium 205. Chichester: John Wiley and Sons, pp. 54-56.
17.
Elliott JC, Holcomb DW, Young RA (1985). Infrared determination of the degree of substitution of hydroxyl by carbonate ions in human dental enamel. Calcif Tissue Int37:372-375.
18.
Featherstone JDB, Rodgers BE (1981). Effect of acetic, lactic and other organic acids on the formation of artificial carious lesions. Caries Res15:377-385.
19.
Featherstone JDB, Mayer I., Driessens FCM, Verbeek RMH, Heijligers HJM (1983). Synthetic apatites containing Na, Mg and CO3 and their comparison with tooth enamel mineral. Calcif Tissue Int35:169-171.
20.
Francis MD, Briner WW, Gray JA ( 1973). Chemical agents in the control of calcification processes in biological systems. In: Hard tissue growth, repair and remineralisation. CIBA Foundation Symposium 11K. Elliott JC, Fitzsimmons DW, editors. Amsterdam: Elsevier, pp. 57-90.
21.
Garnett J., Dieppe P. (1990). The effects of serum albumin on calcium hydroxyapatite crystal growth. Biochem J266:863-868.
22.
Gray JA ( 1962). Kinetics of the dissolution of human dental enamel in acid. J Dent Res41:633-645.
23.
Gray JA ( 1977). Chemical events during cariogenesis. In: Proceedings of the symposium on incipient caries of enamel. Rowe NH, editor. Ann Arbor, Ml: University of Michigan, pp. 19-28.
24.
Gregory TM, Chow LC, Carey CM (1991). A mathematical model for dentine caries-a coupled dissolution-diffusion process. J Res Natl Inst Stds Technol96:593-604.
25.
Hallsworth AS, Robinson C., Weatherell JA (1972). Mineral and magnesium distribution within the approximal carious lesion of dental enamel. Caries Res6:156-168.
26.
Hallsworth AS, Robinson C., Weatherell JA (1973). Loss of carbonate during the first stages of enamel caries. Caries Res7:345-348.
27.
Hendricks SB, Hill WL ( 1942). The inorganic constitution of bone. Science96:255-257.
28.
Ichijo T., Yamashita Y., Terashima T. (1992). Observations on the structural features and characteristics of biological apatite crystals. 2: Observations on the ultrastructure of human enamel crystals. Bull Tokyo Med Dent Univ39:71-80.
29.
Johansen E. (1965). Comparison of the ultrastructure and chemical composition of sound and carious enamel from human permanent teeth. In: Tooth enamel. Stack MV, Fearnhead RW, editors. Bristol: J Wright and Sons, pp. 177-181.
30.
Johnson NW (1967). Some aspects of ultrastructure of early human enamel caries seen with the electron microscope. Arch Oral Biol12:1505-1521.
31.
Kay MI, Young RA, Posner AS (1964). Crystal structure of hydroxyapatite. Nature204:1050-1052.
32.
Koulourides T., Cueto H., Pigman W. (1961). Rehardening of softened enamel surfaces on human teeth by solutions of calcium phosphates. Nature189:226-227.
33.
Kreinbrink AT, Sazavsky CD, Pyrz JW, Nelson DGA, Honkonen RS (1990). Fast magic angle spinning 19F NMR of inorganic fluorides and fluoridated apatitic surfaces. Magnet Res88:267-276.
34.
Kuhl G., Nebergall WH (1963). Hydrogenphosphat und carbonatapatite. Z Anorg Allg Chem324:189-201.
35.
Langdon DJ, Elliott JC, Fearnhead RW (1980). Microradiographic observation of acidic subsurface decalcification in synthetic apatite aggregates. Caries Res14:359-366.
36.
LeGeros RZ (1983). Ultrastructural properties of human enamel apatite. In: Handbook of experimental aspects of oral biochemistry. Lazzar EP, editor. Boca Raton, FL: CRC Press, pp. 59-179.
37.
LeGeros RZ (1984). Incorporation of magnesium in synthetic and in biological apatites. In: Tooth enamel IV Fearnhead RW, Suga S, editors. Amsterdam: Elsevier, pp. 32-36.
38.
LeGeros RZ (1991). Calcium phosphates in dental calculus and dental caries. In: Calcium phosphates in oral biology and medicine. LeGeros RZ, editor. Basel: Karger, pp. 130-153.
39.
Margolis HC, Moreno EC (1985). Kinetic and thermodynamic aspects of enamel demineralisation. Caries Res19:22-35.
40.
Margolis HC, Zhang YP, Lee CY, Kent RL, Moreno EC (1999). Kinetics of enamel demineralization in vitro. J Dent Res78:1326-1335.
41.
Marshall AF, Lawless KR (1981). TEM study of the central dark line in enamel crystallites. J Dent Res60:1773-1782.
42.
McDowell H., Gregory TM, Brown WE (1977). Solubility of Ca5(PO4)3OH in the system Ca(OH)2-H3PO4-H2O at 5, 15, 25 and 37°C. J Res Natl Bur Stds81(A):273-281.
43.
Meckel AH (1968). The nature and importance of organic deposits on dental enamel. Caries Res2:104-114.
44.
Moreno EC, Aoba T. ( 1990). Solubility of human enamel mineral. J Biol Buccale18:195-201.
45.
Moreno EC, Zahradnik RT (1974). Chemistry of enamel subsurface demineralization in vitro. J Dent Res53:226-235.
46.
Myrberg N. (1968). Proton magnetic resonance in human dental enamel and dentine. An experimental investigation using wide line NMR. Trans R Sch Dent Stockholm14:1-62.
47.
Nelson DGA, Jongbloed WL, Arends J. (1984). Crystallographic structure of enamel surfaces treated with topical fluoride agents. TEM and XRD considerations. J Dent Res63:6-12.
48.
Patel PR, Brown WE (1975). Thermodynamic solubility product of human tooth enamel powdered samples. J Dent Res54:728-736.
49.
Poole DFG, Silverstone LM (1973). Remineralisation of enamel. In: CIBA Symposium 11. Amsterdam: Elsevier, pp. 35-56.
50.
Poole DGF, Mortimer KV, Darling AI, Ollis WD (1961). Molecular sieve behaviour of dental enamel. Nature189:998-1000.
51.
Posner AS, Perloff A. (1957). Apatites deficient in divalent cations. J Res Natl Bur Stds58:279-286.
52.
Robinson C., Weatherell JA, Hallsworth AS (1971). Variations in the composition of dental enamel in thin ground sections. Caries Res5:44-57.
53.
Robinson C., Lowe NR, Weatherell JA (1975). Amino acid composition, distribution and origin of "tuft" protein in human and bovine dental enamel. Arch Oral Biol20:29-42.
54.
Robinson C., Weatherell JA, Hallsworth AS (1981). Distribution of magnesium in mature human enamel. Caries Res15:70-77.
55.
Robinson C., Weatherell JA, Hallsworth AS (1983). Alterations in the composition of permanent human enamel during carious attack. In: Demineralisation and remineralisation of the teeth. Leach SA, Edgar WM, editors. Oxford: IRL Press, pp. 209-223.
56.
Robinson C., Kirkham J., Stonehouse NJ, Shore RC (1989). Control of crystal growth during enamel maturation. Connect Tissue Res22:139-145.
57.
Robinson C., Hallsworth AS, Shore RC, Kirkham J. (1990). Effect of surface-zone deproteinisation on the access of mineral ions into subsurface lesions of human enamel. Caries Res24:226-230.
Robinson C., Weatherell JA, Kirkham J. (1995b). The chemistry of dental caries. In: Dental enamel: from formation to destruction. Robinson C, Kirkham J, Shore RC, editors. Boca Raton, FL: CRC Press, pp. 223-243.
60.
Robinson C., Brookes SJ, Shore RC, Kirkham J. (1998). Identification of human serum albumin in human caries lesions of enamel: the role of putative inhibitors of remineralisation. Caries Res32:193-199.
61.
Robinson C., Kirkham J., Shore RC, Brookes SJ, Wood SR ( 2000). Enamel matrix function and the tuft enigma: a role in directing enamel tissue-architecture: a partial sequence of human ameloblastin. In: Chemistry and biology of mineralised tissues. Proceedings of the sixth international conference. Goldberg M, Boskey A, Robinson C, editors. Vittel, France, American Academy of Orthopaedic Surgeons, pp. 209-213.
62.
Rolla G., gaard B. (1986). How important is CaF2 in the cariostatic mechanism of fluoride in vivo? In: Factors relating to the demineralisation and remineralisation of teeth. Leach SA, editor. Oxford: IRL Press, pp. 45-50.
63.
Shellis RP, Wahab FK, Heywood BR (1993). The hydroxyapatite ion activity product in acid solutions equilibrated with human enamel at 37°C. Caries Res27:365-372.
64.
Silverstone LM (1967). Observations on the dark zone in early enamel caries and in artificial caries-like lesions. Caries Res1:261-274.
65.
Silverstone LM (1968). The surface zone in caries and in caries like lesions produced in vitro. Br Dent J125:145-157.
66.
Silverstone LM (1983). Remineralisation and enamel caries: significance of fluoride and effect on crystal diameters. In: Demineralisation and remineralisation of the teeth. Leach SA, Edgar WM, editors. Oxford: IRL Press, pp. 185-205.
67.
Silverstone LM, Poole DFG (1968). The effect of saliva and calcifying solutions upon the histological appearance of enamel caries. Caries Res2:87-96.
68.
Ten Cate JM (1983). The effect of fluoride on enamel deand remineralisation. In: Cariology. Guggenheim B, editor. Basel: Karger, pp. 231-236.
69.
Ten Cate JM, Duijsters PPE (1983). The influence of fluoride in solution on tooth demineralisation: 1. Chemical data. Caries Res17:193-199.
70.
Terpstra RA, Driessens FCM (1986). Magnesium in tooth enamel and synthetic apatites. Calcif Tissue Int39:348-354.
71.
Theuns HM, Driessens FCM, van Dijk JWE, Groeneveld A. (1986). Experimental evidence for a gradient in the solubility and in the rate of dissolution of human enamel. Caries Res20:24-31.
72.
Van Dijk JWE, Borggreven JMPM, Driessens FCM (1979). Chemical and mathematical simulation of caries. Caries Res13:169-180.
73.
Verbeek RMH (1986). Minerals in human enamel and dentine. In: Tooth development and caries. Driessens FCM, Woltgens JMH, editors. Boca Raton, FL: CRC Press, pp. 95-153.
74.
Vogel GL, Cary CM, Chow LC, Gregory TM, Brown WE (1988). Micro-analysis of mineral saturation within enamel during lactic acid demineralization. J Dent Res67:1172-1180.
75.
von der Fehr FR, Loe H., Theilade E. (1970). Experimental caries in man. Caries Res4:131-148.
76.
Weatherell JA, Robinson C. (1973). The inorganic composition of teeth. In: Biological mineralisation. Zipkin I, editor. New York: John Wiley, pp 43-74.
77.
Weatherell JA, Robinson C., Hiller CR (1968a). Distribution of carbonate in thin sections of dental enamel. Caries Res2:1-9.
78.
Weatherell JA, Weidmann SM, Eyre DR ( 1968b). Histological appearance and chemical composition of enamel protein from mature human molars. Caries Res2:281-293.
79.
Weatherell JA, Robinson C., Hallsworth AS (1972). Changes in the fluoride concentration of the labial enamel surface with age. Caries Res6:312-324.
80.
Weatherell JA, Deutsch D., Robinson C., Hallsworth AS (1977). Assimilation of fluoride by enamel through the life of the tooth. Caries Res11 (Suppl 1):85-115.
81.
Weidmann SM, Hamm SM ( 1965). Studies on the enamel matrix of mature teeth. In: Tooth enamel. Stack MV, Fearnhead RW, editors. Bristol: John Wright and Sons, pp. 83-90.
82.
Winand L., Dallemagne MJ, Duyckaerts G. (1961). Hydrogen bonding in apatitic calcium phosphates. Nature190:164-165.
83.
Young RA (1975). Biological apatite vs. hydroxyapatite at the atomic level. Clin Orthop113:249-262.
84.
Young RA, Spooner S. (1969). Neutron diffraction studies of human tooth enamel. Arch Oral Biol15:47-63.
85.
Zahradnik RT, Moreno EC, Burke EJ (1976). The effect of salivary pellicle on enamel subsurface demineralization in vitro. J Dent Res55:664-670.
