Abstract: Nanocrystalline apatites exhibit a very fragile structured hydrated surface layer which is only observed in aqueous media. This surface layer contains mobile ionic species which can be easily exchanged with ions from the surrounding fluids. Although the precise structure of this surface layer is still unknown, it presents very specific spectroscopic characteristics. The structure of the hydrated surface layer depends on the constitutive mineral ions: ion exchanges of HPO4 2- ions by CO3
2- ions or of Ca2+ by Mg2+ ions result in a de-structuration of the hydrated layer and modifies its spectroscopic characteristics. However, the original structure can be retrieved by reverse exchange reaction. These alterations do not seem to affect the apatitic lattice. Stoichiometric apatite also shows HPO4 2- on their surface due to a surface hydrolysis after contact with aqueous solutions. Ion exchange is also observed and the environments of the surface carbonate ions seem analogous to
that observed in nanocrystalline apatites. The formation of a hydrated layer in aqueous media appears to be a property common to apatites which has to be taken into account in their reactivity and biological behavior.
Abstract: Our earlier studies showed that several ions inhibit the crystal growth of apatite and
promote the formation of amorphous calcium phosphates (ACP). These ions include: magnesium (Mg), zinc (Zn), stannous (Sn), ferrous (Fe), carbonate (CO3), pyrophosphate (P2O7). The purpose of this study was to investigate the effect of combination of these ions (e.g., Mg & CO3, Mg &
P2O7, Mg & Zn, etc) on the formation and stability of ACP. ACP compounds containing the different ions were prepared at 25 and 37oC according to the method we previously described. Chemical stability was investigated by suspending the different ACP preparations in solutions with or without inhibitory ions. Thermal stability was determined by sintering the ACP at different temperatures. Dissolution properties were determined in acidic buffer. The ACP before and after chemical or thermal treatment were analyzed using X-ray diffraction, infrared spectroscopy, and
thermogravimetry. Results showed synergistic effects of inhibitory ions on the formation of ACP. ACP materials, regardless of their composition, remained amorphous even after heat treatment at 400oC. Transformation of ACP to other calcium phosphate phases depended on the pH and on the solution composition.
Abstract: Bioactive calcium phosphate (Ca-P) formation in bioceramics surfaces in simulated body fluid (SBF) and in rabbit muscle sites was investigated. The examined bioceamics included most commonly used bioglass®, A-W glass-ceramics and calcium phosphates in orthopedic and dental applications. The Ca-P cyrstal structures were examined with single crystal diffraction patterns in transmission electron microscopy, which reduced possibility of misidentifying Ca-P phases. The
experimental results show that capability of Ca-P formation considerably varied among bioceramics, particularly in vivo. Octacalcium phosphate (OCP) was revealed on the all types of bioceramics in vitro and in vivo experiments. This work leads us to rethink how to evaluate bioactivity of bioceramics and other orthopedic materials which exhibit capability of osteoconduction by forming direct bonding with bone.
Abstract: The progression of the setting reaction of a tetracalcium phosphate (TTCP) –dicalcium phosphate dihydrate (DCPD) rapid setting cement was investigated as a function of time. Compressive strength and extent of conversion to hydroxyapatite (HA) were obtained at different incubation times. The results indicated a rapid development of both strength and HA conversion in the early stages of the reaction, which slowed down after 4 h, presumably as a result of HA formation on the surface of the reactants. This hypothesis was supported by scanning electron microscopy examination of cement fracture surfaces.
Abstract: This study sought to examine the efficiency of coating cement powder reactants in order to reduce the solubility rate of reactants and thereby increase setting times of cement systems. In this investigation magnesium and sodium stearate salts were used to coat the highly soluble monocalcium phosphate monohydrate (MCPM) powder component of a hydraulic brushite forming calcium phosphate cement system with b-tricalcium phosphate (b-TCP) as other component. The results showed that stearate coating of the MCPM reactant could lead to a 100%
increase in setting and working times without affecting compressive strength of the set cement when applied with the appropriate P/L-ratio.
Abstract: In this paper, a low concentration of Hydrogen Peroxide (H2O2) was added to the hydroxyapatite ceramics to develop HA/H2O2 compound. The HA/H2O2 was tested for the whitening and deodorizing ability. HA/H2O2 composite was added with glycerin and was tested on the enamel layer for lightness changes on the tooth layer. The lightness result was compared with 100[ppm] of H2O2 treatment by
Spectro Color Meter and enamel layers structure observation by optical microscope. In deodorization test, 20[g] of clove garlic and slice garlic were identified for garlic aroma peak. 20[g] of HA/H2O2 compound, HA alone and charcoal respectively were tested for the garlic aroma adsorption ability.
Identification and quantification of the garlic aroma peak area decrease was observed by gas chromatography. In the whitening result, HA/H2O2 compound and H2O2 alone treatment obtained 68 and 67 respectively. From the structure observation, HA/H2O2 composite treatment was the best since the smooth and unharmed enamel layer of the tooth was observed. Deodorization ability for HA/H2O2 compound has the similarity rate as charcoal at 82.3[%]. The HA/H2O2 composite has an ability of whitening and deodorizing at even low concentration.
Abstract: Zinc-containing calcium phosphate ceramics with a (Ca+Zn)/P molar ratio of 1.67
(ZnHAP ceramics) were synthesized to clarify the main phase for zinc release. ZnHAP ceramics with a zinc content at or more than 0.20 wt% contained zinc-containing tricalcium phosphate. The ion activity product of monophasic ZnHAP ceramic containing at or less than 0.13 wt% of zinc corresponded to that of pure HAP ceramic. The presence of tricalcium phosphate (TCP) phases was
necessary condition for ZnHAP ceramics to release zinc. The coexistence of TCP phases in the ZnHAP ceramics meant that a phase with a (Ca+Zn)/P molar ratio higher than 1.67 also coexisted. Although the phase was assumed to be zinc oxide, zinc was not concentrated anywhere in the ZnHAP ceramics including grain boundaries.
Abstract: The purpose of this study is to investigate the remineralization of enamel in the human tooth by fissure sealant containing various amount of hydroxyapatite. Prior to remineralization experiments, the necessary requirements of the dental fissure sealant, the curing depth and the curing time, were measured with the content of the hydroxyapatite according to the standard of ISO 6874.
Various amount of hydroxyapatite was mixed uniformly using sonicator up to 20 wt% to the fissure sealant. In spite both the curing time and the curing depth were decreased with increasing the content of hydroxyapatite, all samples were satisfied the ISO requirements. Remineralization experimental samples were produced by bonding fissure sealant containing various amount of hydroxyapatite to human tooth enamel using manufacturer’s information. After exposure to the simulated body fluid at 36.5oC for 4 weeks, the bonding strength and the surface morphology were examined using Instron and scanning electronic microscope, respectively. The bonding strength between the fissure sealant and the human teeth was drastically enhanced with the amount of hydroxyapatite. The remineralization zone could be observed along with the boundary of hydroxyapatite and fissure sealant using a scanning electronic microscope.
Abstract: Composite material composed of hydroxyapatite (HAp) and structural proteins, such as type I collagen or cross-linked gelatins, were synthesized at 37.4°C by hydrolysis of alpha tricalcium phosphate (α-TCP) in the presence of these protein structures. X-ray diffraction (XRD)and isothermal calorimetry were used as tools to evaluate the rate of HAp formation. Rates of HAp formation depend on protein structure. Gelatin enhances HAp formation while collagen delays it.
Changes in pH during the hydrolysis α-TCP are unlikely to have an aggressive effect on the surrounding tissue. The presence of the protein improves the ductility of the HAp/protein composite but it decreases the tensile strength.