Thermal study and structural characterization of biological hydroxyapatite (HA) samples were done as well as their comparison with commercial and synthetic samples in this study. The X-ray micro analyser shows that all three samples of human teeth (HT1–HT3) contain two types of HA structures with different crystallite sizes, unlike sample of bovine thigh-bone (BTB). The bone sample was composed only of one HA phase with varied porosity. The molar Ca/P ratio in biological samples was lower compared to theoretical ratio for pure HA; moreover, in the case of teeth, Ca/P ratio varyies between the centre and the periphery of the cross-sectional samples. Thermogravimetry of the biological samples showed mass decreases—three regions for the bone and four regions for the teeth. In comparison, commercial HA has only two-step weight loss and synthetic HA three-step weight loss. After the calcination up to 1280 °C all the samples of teeth transformed into whitlockite, β-(Ca,Mg)3(PO4)2 (98 wt%) and 2 wt% HA. Besides, HT3 contained further trace amount of hilgenstockite (HIL, Ca4P2O9). The sample BTB partly transited from natural HA into HIL (6 wt%) and lime, CaO (14 wt%). X-ray powder diffraction (XRD) proved occurrence of HIL (9 wt%) beside stability part HA (91 wt%) in the commercial HA after thermal treatment but the synthetic HA composed from Ca3(PO4)2 (74 wt%) and HA (26 wt%).
1. Palmer, LC, Newcomb, CJ, et al. Biomimetic systems for hydroxyapatite mineralization inspired by bone and enamel. Chem Rev. 2008;108:4754–4783. .
2. Dorozhkin, SV. Calcium orthophosphates in nature, biology and medicine. Materials. 2009;2:399–498. .
3. LeGeros, RZ. Formation and transformation of calcium phosphates: relevance to vascular calcification. Z Kardiol. 2001;90:116–124. .
4. Ito, A, Onuma, K. Crystal growth technology. London: Wiliam Andrew Publishing; 2003.
5. Chen, ZF, Darvell, BW, Leung, VWH. Hydroxyapatite solubility in simple inorganic solutions. Arch Oral Biol. 2004;49:359–367. .
6. Yujiro, W, Toshiyuki, I, Yasushi, S. Type-A zeolites with hydroxyapatite surface layers formed by an ion exchange reaction. J Eur Ceram Soc. 2006;26:469–474. .
7. Reddy, MP, Venugopal, A. Hydroxyapatite photocatalytic degradation of calmagite (an azo dye) in aqueous suspension. Appl Catal B. 2007;69:164–170. .
8. Baillez, S, Nzihou, A, Bernache-Assolant, D. Removal of aqueous lead ions by hydroxyapatites: equilibria and kinetic processes. J Hazard Mater. 2007;139:443–446. .
9. Reddy, MP, Venugopal, A, Subrahmanyam, M. Hydroxyapatite-supported Ag-TiO2 as Escherichia coli disinfection photocatalyst. Water Res. 2007;41:379–386. .
10. Omelon, SJ, Grynpas, MD. Relationships between polyphosphate chemistry, biochemistry and apatite biomineralization. Chem Rev. 2008;108:4694–4715. .
11. Rey, C, et al. Chemical diversity of apatites. Adv Sci Technol. 2006;49:27–36. .
12. Daculsi, G, Bouler, JM, LeGeros, RZ. Adaptive crystal formation in normal and pathological calcifications in synthetic calcium phosphate and related biomaterials. Int Rev Cytol. 1997;172:129–191. .
13. LeGeros, RZ. Calcium phosphates in oral biology and medicine. Basel: Karger; 1991.
14. Prakash, KH, et al. Apparent solubility of hydroxyapatite in aqueous medium and its influence on the morphology of nanocrystallites with precipitation temperature. Langmuir. 2006;22:11002–11008. .
15. Sanosh, KP, et al. Preparation and characterization of nano-hydroxyapatite powder using sol–gel technique. Bull Mater Sci. 2009;32:465–470. .
16. Yoon, SY, et al. Synthesis of hydroxyapatite whiskers by hydrolysis of α-tricalcium phosphate using microwave heating. Mater Chem Phys. 2005;91:48–53. .
17. Earl, JS, et al. Hydrothermal synthesis of hydroxyapatite. J Phys Conf Ser. 2006;26:268–271. .
18. Kaloustian, J, et al. The use of thermal analysis in determination of some urinary calculi of calcium oxalate. J Therm Anal Calorim. 2002;70:959–973. .
19. Madhurambal, G, Subha, R, Mojumdar, SC. Crystallization and thermal characterization of calcium hydrogen phosphate dihydrate crystals. J Therm Anal Calorim. 2009;96:73–76. .
20. Paulik, F, et al. Investigation of the composition and crystal structure of bone salt by derivatography and infrared spectrophotometry. Hoppe Seyler’s Z Physiol Chem. 1969;350:418–426. .
21. Mezahi, FZ, et al. Dissolution kinetic and structural behaviour of natural hydroxyapatite vs. thermal treatment. J Therm Anal Calorim. 2009;95:21–29. .
22. Mitsionis, AI, Vaimakis, TC. A calorimetric study of the temperature effect on calcium phosphate precipitation. J Therm Anal Calorim. 2010;99:785–789. .
23. Holager, J. Thermogravimetric examination of enamel and dentin. J Dent Res. 1970;49:546–548. .
24. JCPDS PDF-2 database, release 54. Newton Sq.: International Centre for Diffraction Data; 2004.
25. Diamanti, I, et al. Effect of fluoride and of calcium sodium phosphosilicate toothpastes on pre-softened dentin demineralization and remineralization in vitro. J Dent. 2010;38:671–677. .
26. Hattab, FN. The state of fluorides in toothpastes. J Dent. 1989;17:47–54. .
27. LeGeros, RY, Bonel, G, Legros, R. Types of H2O in human enamel and in precipitated apatites. Calcif Tiss Res. 1987;26:111–118. .
28. Wang, L, Nancollas, GH. Calcium orthophosphates: crystallization and dissolution. Chem Rew. 2008;108:4628–4669. .
29. McConnell, D. Apatite. Vienna: Springer; 1973.
30. Posner, AS. Crystal chemistry of bone mineral. Physiol Rev. 1969;49:760–792.
31. Shi, D. Biomaterials and tissue engineering. Berlin: Springer; 2004.
32. Aras, NK, Yiimaz, G, Alkan, S, Korkusuz, F. Trace elements in human bone determined by neutron activation analysis. J Radioanal Nucl Chem. 1999;239:79–86. .