| Summary: | 博士 === 高雄醫學大學 === 牙醫學研究所 === 99 === Background: Fluoridated hydroxyapatite (FHA) occurs naturally in both bone and tooth. The FHA composite has molecules of non-FHA and FHA with different degrees of fluoridation, Ca10(PO4)6(OH)2-2xF2x (0< x< 1). The simplest formulation of FHA molecule is Ca10(PO4)6(OH)F. The FHA can form apatite supramolecule, nCa10(PO4)6(OH)2-2xF2x (n> 2, 0< x< 1), through physical and/or chemical interactions of the FHA with either one apatite or more.
Objectives: In current studies, we have investigated the molecular characteristics and the sintering mechanism of sintered FHA composites based on HA-CaF2 system. To do so, we have designed two approaches. First, we need to determine the molecular characteristics of FHA composites. Then, we explore the sintering mechanism of highly densified FHA composites.
Materials & Methods: Chapter 1 is dedicated to the molecular characteristics of the FHA composites assayed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) techniques. The FHA composites were prepared by sintering at 700°C for 2 hours with different combinations of HA and CaF2. Chapter 2 is to investigate the sintering mechanism of highly densified FHA composites by density test, differential thermal analysis (DTA), thermogravimetric analysis (TGA), XRD and FT-IR techniques. In this regard, FHA composites were sintered equal to or greater than 700°C for 2 hours with HA and CaF2.
Results: Unsintered HA and CaF2 mixtures show both the OH stretching mode vibration band (3,572 cm-1) and OH liberational mode vibration band (634 cm-1), without OH…F…HO or OH…F hydrogen absorption band under FT-IR analysis. Sintered FHA composites have the FHA pattern under small angle XRD detection around apatite lattice face 300. FHA composites show the OH…F…HO and/or the OH…F hydrogen absorption band under the FT-IR analysis. The highly densified FHA composites were obtained with HA 70 wt% and CaF2 30 wt%, when the sintering temperature > 900°C. With the sintering temperature > 1100°C, the phase change of the FHA composite into tricalcium phosphate (TCP) is obvious. FT-IR analysis shows loss of OH…F…HO hydrogen absorption band when the TCP phase appears. The DTA result shows endothermal reaction at 1180°C without weight loss under the TGA investigation.
Conclusions: Unsintered HA and CaF2 mixtures have no obvious change in OH stretching or liberational mode vibration. With gradual increase of CaF2 wt%, the sequence of FT-IR bands show OH…F stretching mode vibration first, then followed by OH…F…HO liberational mode vibration and, finally, the OH…F liberational mode vibration. When heating > 1100°C, the highly densified FHA composites lose the OH…F…HO liberational mode vibration. Together, we revised the FHA supramolecular model of Freund and Knobel. After molecular characteristic and sintering mechanism research, we came up with a new apatite supramolecular model, the W-apatite supramolecular model (W= OH, F).
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