Effect of Solution Composition on Morphological and Structural Features of Carbonated Calcium Apatites

Abstract

The composition of enamel mineral corresponds to that of a calcium carbonato-apatite. For insight to be gained into the precipitation of carbonato-apatites having specific properties (crystal size, morphology, and carbonate incorporation into the crystal lattice), apatites were prepared at 80°C in aqueous systems having various CO₃ concentrations and pH values of around 7.5 or 10.5 (± 0.5). The various preparations had a wide range (0.005 to 0.19) of CO₃/Ca molar ratios that bracket the ratios found in porcine enamel mineral at various developmental stages. Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction analyses showed that the calcium apatites precipitating at neutral pH incorporated the carbonate into both the hydroxyl and phosphate ion sites in their lattices (A,B-types), whereas the preparations made at the alkaline pH (high OH-CO₃ ^2- competition) or in the presence of fluoride (F^--CO₃ ^2- competition) yielded only the B-type carbonato-apatite. It was also ascertained that the size and morphology of the carbonato-apatites, assessed by specific surface area determination and high-resolution electron microscopy, were highly dependent on the driving force for precipitation and the presence of regulators (CO₃ ^2- and F^-) in solution. In neutral media, early precipitates were thin-ribbon in appearance, but grew into crystals having flattened-hexagonal cross-sections. In the presence of fluoride or in alkaline media, acicular apatite crystals, precipitated initially, grew into large rod-like carbonato-apatites having a symmetric-hexagonal cross-section. In both neutral and alkaline solutions, carbonate inhibited the growth of apatite crystals along their c axis, leading to the formation of bulkier crystals. The formation of carbonato-apatites at the neutral pH and their properties are consistent with observations made on enamel minerals formed in the early developmental stages.

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References

Aoba, T. and Moreno, E.C. (1984): Preparation of Hydroxyapatite Crystals and Their Behavior as Seeds for Crystal Growth, J Dent Res 63:874-880.

Aoba, T. and Moreno, E.C. (1987): The Enamel Fluid in the Early Secretory Stage of Porcine Amelogenesis. Chemical Composition and Saturation with Respect to Enamel Mineral, Calcif Tissue Int 41:86-94.

Aoba, T. and Moreno, E.C. (1989): Mechanism of Amelogenic Mineralization in Minipig Secretory Enamel. In: Proceedings of Tooth Enamel V, R.W. Fearnhead , Ed., Yokohama: Florence Pub., pp. 163-168.

Aoba, T. and Moreno, E.C. (1990): Changes in the Nature and Composition of Enamel Mineral during Porcine Amelogenesis, Calcif Tissue Int (in press).

Bonel, G. and Montel, G. (1964): Sur une Nouvelle Apatite Carbonatee Synthetique , C R Acad Sc Paris 258:923-926.

Borneman-Starinkevitch, I.D. and Belov, N.V. (1953): On Carbonate Apatites, Dolk Akad Nauk USSR 90:89-92.

Brown, W.E. ; Mathew, M. ; and Tung, M.S. (1981): Crystal Chemistry of Octacalcium Phosphate, Prog Crystal Growth Charact 4:59-87.

Chickerur, N.S. ; Tung, M.S. ; and Brown, W.E. (1980): A Mechanism for Incorporation of Carbonate into Apatite, Calcif Tissue Int 32:55-62.

Conway, E.J. (1950): Microdiffusion Analysis and Volumetric Error, 3rd ed., New York: van Nostrand, pp. 201-214.

10.

Coolidge, T.B. and Jacobs, M.H. (1957): Enamel Carbonate in Caries, J Dent Res 36:765-768.

11.

De Mul, F.F.M. ; Hottenhuis, M.H.J. ; Bouter, P. ; Greve, J. ; Arends, J. ; and Ten Bosch, J.J. (1986): Micro-Raman Line Broadening in Synthetic Carbonated Hydroxyapatite, J Dent Res 65:437-440.

12.

Doi, Y. ; Moriwaki, Y. ; Aoba, T. ; Okazaki, M. ; Taka-Hashi, J. ; and Joshin, K. (1982): Carbonate Apatites from Aqueous and Non-aqueous Media Studied by ESR, IR, and X-ray Diffraction: Effect of NH4+ Ions on Crystallographic Parameters, J Dent Res 61:429-434.

13.

Dykes, E. and Elliott, J.C. (1971): The Occurrence of Chloride Ions in the Apatite Lattice of Holly Springs Hydroxyapatite and Dental Enamel, Calcif Tissue Res 7:241-248.

14.

Elliott, J.C. (1963): Some Observations on the Crystal Chemistry of Carbonate-containing Apatites, Adv Flu Res Dent Caries Prev 1:277-282.

15.

Elliott, J.C. (1964): The Crystallographic Structure of Dental Enamel and Related Apatites, Ph.D. Thesis, University of London .

16.

Elliott, J.C. (1965): The Interpretation of the Infrared Absorption Spectra of Some Carbonate-containing Apatites. In: Tooth Enamel , M.V. Stack and R.W. Fearnhead , Eds., Bristol : John Wright, pp. 20-22.

17.

Elliott, J.C. ; Holcomb, D.W. ; and Young, R.A. (1985): Infrared Determination of the Degree of Substitution of Hydroxyl by Carbonate Ions in Human Dental Enamel, Calcif Tissue Int 37:372-375.

18.

Fowler, B.O. ; Moreno, E.C. ; and Brown, W.E. (1966): Infrared Spectra of Hydroxyapatite, Octacalcium Phosphate and Pyrolysed Octacalcium Phosphate, Arch Oral Biol 11:477-492.

19.

Freund, F. and Knobel, R.M. (1977): Distribution of Fluorine in OHAp Studied by Infrared Spectroscopy, J Chem Soc Dalton 1977:1136-1140.

20.

Hallsworth, A.S. ; Weatherell, J.A. ; and Robinson, C. (1973): Loss of Carbonate during the First Stages of Enamel Caries, Caries Res 7:345-348.

21.

Hiller, C.R. ; Robinson, C. ; and Weatherell, J.A. (1975): Variations in the Composition of Developing Rat Incisor Enamel, Calcif Tissue Int 18:1-12.

22.

Holcomb, D.W. and Young, R.A. (1980): Thermal Decomposition of Human Tooth Enamel, Calcif Tissue Int 31:189-201.

23.

Kay, M.I. ; Young, R.A. ; and Posner, A.S. (1964): Crystal Structure of Hydroxyapatite, Nature 204:1050-1052.

24.

Kerebel, B. ; Daculsi, G. ; and Kerebel, L.M. (1979): Ultrastructural Studies of Enamel Crystallites , J Dent Res 58B :844-850.

25.

Legeros, R.Z. (1981): Apatites in Biological Systems, Prog Crystal Growth Charact 4:1-45.

26.

Legeros, R.Z. and Suga, S. (1980): Crystallographic Nature of Fluoride in Enameloids of Fish, Calcif Tissue Int 32:169-174.

27.

Legeros, R.Z. ; Trautz, O.R. ; Klein, E. ; and Legeros, J.P. (1969): Two Types of Carbonate Substitution in the Apatite Structure, Experientia 24:5-7.

28.

Legeros, R.Z. ; Trautz, O.R. ; Legeros, J.P. ; Klein, E. ; and Shirra, W.P. (1967): Apatite Crystallites: Effects of Carbonate on Morphology, Science 155:1409-1411.

29.

Legeros, R.Z. and Tung, M.S. (1983): Chemical Stability of Carbonate- and Fluoride-containing Apatites, Caries Res 17 :419-429.

30.

Little, M.F. and Brudevold, F. (1958): A Study of the Inorganic Carbon Dioxide in Intact Human Enamel, J Dent Res 37 :991-1000.

31.

Lowenstam, H.A. and Weiner, S. (1989): On Biomineralization, New York : Oxford Univ Press, pp. 175-188.

32.

McClellan, G.H. and Lehr, J.R. (1969): Crystal-chemical Investigations of Natural Apatites , Am Min 54:1374-1391.

33.

Nelson, D.G.A. and Barry, J.C. (1989): High Resolution Electron Microscopy of Nonstoichiometric Apatite Crystals, Anat Rec 224:265-276.

34.

Nelson, D.G.A. ; Barry, J.C. ; Shields, C.P. ; Glena, R. ; and Featherstone, J.D.B. (1989): Crystal Morphology, Composition, and Dissolution Behavior of Carbonated Apatites Prepared at Controlled pH and Temperature, J Colloid Interf Sci 130:467-479.

35.

Nelson, D.G.A. and Featherstone, J.D.B. (1982): Preparation, Analysis, and Characterization of Carbonated Apatites, Calcif Tissue Int 34:S69-S81.

36.

Nylen, M.U. ; Eanes, E.D. ; and Omnell, K.A. (1963): Crystal Growth in Rat Enamel, J Cell Biol 18:109-123.

37.

Okazaki, M. (1983): F-CO3 Interaction in IR Spectra of Fluoridated CO3-Apatites, Calcif Tissue Res 35:78-81.

38.

Okazaki, M. ; Moriwaki, Y. ; Aoba, T. ; Doi, Y. ; Taka-Hashi, J. ; and Kimura, H. (1982): Crystallinity Changes of CO3-Apatites in Solutions at Physiological pH, Caries Res 16 :308-314.

39.

Simpson, D.R. (1972): Problems of the Composition and Structure of the Bone Minerals, Clin Orthop Rel Res 86:260-286.

40.

Vignoles, M. and Bonel, G. (1978): Sur la Localisation des Ions Fluorure dans les Carbonate-apatites de Type B, C R Acad Sc Paris 287:321-324.

41.

Vignoles, M. ; Bonel, G. ; Holcomb, D.W. ; and Young, R.A. (1988): Influence of Preparation Conditions on the Composition of Type B Carbonated Hydroxyapatite and on the Localization of the Carbonate Ions, Calcif Tissue Int 43:33-40.

42.

Vignoles, M. ; Bonel, G. ; and Young, R.A. (1987): Occurrence of Nitrogenous Species in Precipitated B-type Carbonated Hydroxyapatites, Calcif Tissue Int 40:64-70.

43.

Vogel, A.J. (1961): Quantitative Inorganic Analysis, 3rd ed., New York: John Wiley & Sons, p. 810.

44.

Wallaeys, R. (1954): Etude d'une Apatite Carbonatee Obtenue par Synthese dans L'Etat Solide. In: Silicon, Sulphur, Phosphates, Coll Int Union of Pure and Appl Chem, Miinster, Weinheim : Verlag Chemie, pp. 183-190.

45.

Weatherell, J.A. ; Robinson, C. ; and Hiller, C.R. (1968): Distribution of Carbonate in Thin Sections of Dental Enamel, Caries Res 2:1-9.

46.

White, W.B. (1974): The Carbonate Minerals. In: The Infrared Spectra of Minerals, V.C. Farmer , Ed., London: Mineralogical Soc, pp. 227-284.

47.

Young, R.A. (1980): Large Effects from Small Structural Differences in Apatites, Proc Int Cong Phosphorus Compounds 2 :73-88.