Key Engineering Materials Vols. 330-332

Abstract: Natural biological hard tissues are nanocomposites of proteins and calcium hydroxyapatite (HAp) with superior strength and bioresorbabilities. Nanometer scale hyroxyapatite is the key material to manufacture bioresorbable bone substitute. An attempt was conducted to synthesis nano-crystalline hydroxyapatite with a hydrothermal chemical method. The prepared nano-crystalline HAp was characterized for its phase purity and nanoscale morphological structure by XRD, TEM and FTIR. The obtained results indicated that hydrothermal synthesized nano-crystalline HAp was pure single phased HAp with a diameter of 20 to 50nm and length range between 50 to 200nm and each HAp particle was observed to be a monocrystal of HAp. It’s suggested that hydrothermal treatment may be an effective method to get pure and nice crystallized nano-sized stoichiometric hydroxyapatite.

Abstract: The purpose of this study is to examine the inhibitory effects of nano-HA on the caries-inducing properties of a four-organism bacterial consortium in vitro. A series of in vitro anticarious experiments have been carried out by using a continuous culture system. Streptococcus mutans, Streptococcus sanguis, Actinomyces viscosus, Lactobacillus rhamnosus have been chosen as the experimental bacteria. After 48 hours, the dental plaque surface structure is observed with the scan electron microscope and the bacterial colonization was evaluated on dental plaque. The results show that Spherical nano-HA and mixed nano-HA are proved to be effective in anticarious experiments, and especially spherical nano-HA is more striking. It is able to damage the formation of biofilms (dental plaque), postpone or end the process of acid generation of bacteria metabolism. After 7 days, the demineralization of the enamel has been detected by using TEM. The spherical nano-HA might have a remineralization to early caries to prevent and decrease caries.

Abstract: Hydroxyapatite, HA, with crystal size smaller than 10 nm was synthesized by dropwise addition of calcium nitrate and ammonium phosphate under controlled conditions. Powder was composed by agglomerates of nano-particles with specific surface area higher than 200 m2/g. HA samples had a main pore size distribution centered at 13-15 nm with a secondary mode centered at 3-5 nm. High resolution TEM revealed that individual particles had nearly spherical shapes and were mainly composed of a crystalline core and an amorphous external component. EXAFS measurements confirmed that the short range order of those HA nanocrystals was similar to that of HA sintered at high temperature. HA powder with small particle size incorporates in its structure more water and carbonate ions than HA prepared in normal conditions.

Abstract: The influences of temperature and time on sintering behaviour of nanosized HAP powder were investigate in this paper. The calcium hydroxyapatite powder, with the average crystallite size of 34 ± 1 nm, was uniaxially pressed at a pressure of 500 MPa. Obtained green compacts were sintered at temperature ranging from 1000°C to 1200°C in air atmosphere at various times. According to the results of scanning electron microscopy, X-ray and FTIR analyses, it is shown that HAP compacts with dense microstructure and average grain size below 250 nm is obtained.

Abstract: In this work, nano-sized strontium containing tricalcium phosphate (SrTCP) particles with different strontium content were prepared using co-precipitation method in an ice-water bath and then 800°C calcination. The AAS results show that the relative Sr/(Sr+Ca) ratios are consistent with the amount of strontium added in the initial solution but larger than the designed molar percentage. The TEM micrographs demonstrate the size of the SrTCP particles is in the region of 150-400 nm while the pure TCP particle is about 500nm. The SEM photographs show the morphology of the particles before and after incorporation of strontium and it is obvious that the particle size of SrTCP decrease with the increasing of strontium content.

Abstract: The aim of this study is to describe the remineralization effect of the nano-HA toothpaste on artificial caries. The artificial dental caries is made using sour solution. The demineralized teeth specimen is put into five kinds of toothpaste solution respectively for 5 days and 10 days, which are: solution of containing needle like nano-HA, solution of containing spherical nano-HA, solution of general HA, fluorine sodium solution and physiological saline. The hardness of specimen is measured and the surface morphology is characterized by SEM. The remineralized test indicates that the nano-HA toothpaste can enhance the hardness of artificial caries and improve the remineralization of artificial caries. The SEM analysis shows that the cavities and defects of enamel surface are decreased and many mineral salts are sedimentated, which indicate that the nano-HA could promote remineralization for the demineralized enamel.

Abstract: This paper reports synthesis of hydroxyapatite nanoparticles by three precipitation methods. Homogeneous aqueous solution of Ca(NO3)2 and H3PO4 was used as precursor solution, and NH3•H2O was precipitator. Calcium deficient hydroxyapatite nanorods were obtained by adding the precipitator into precursor solution, near stoichiometric hydroxyapatite nanoparticles were derived from adding precursor solution into the precipitator, and smaller hydroxyapatite nanoparticles were prepared by adding precipitator and precursor solution simultaneously into a reaction vessel. The stoichiometry of hydroxyapatite was mainly affected by pH at precipitation reaction process. The crystal size and shape of hydroxyapatite particles was related to Ostwald ripening. The stoichiometry and morphology of hydroxyapatite nanoparticles can be controllable by selecting suitable coprecipitation process.

Abstract: Several studies have reported the on dental erosive potential of sports drinks with a low pH. Therefore, there is a need for new components that can reduce the erosive potential of a sports drink. Hydroxyapatites (HA) are the major components of dental enamel and bone mineral as biological apatites. In addition, HA contains a significant amount of calcium and phosphate, which can promote remineralization. Hence, some remineralization of the enamel surface can be expected if nano-sized hydroxyapatite (nano-HA) is added to a sports drink. The aim of this study was to evaluate the remineralization effects of sports drinks containing nano-HA in vitro. The crowns of extracted human molars were embedded in acrylic resin and then ground flat and polished. A commercially available sports drink (Powerade, Coca-Cola, South Korea) was purchased from a local supermarket. Nano-HA was added at a concentration of 0.05%, 0.25%, and 0.5%. Deionized water (DW) was used as the negative control. The pH of each solution was measured by a pH-meter at room temperature. The enamel specimens were immersed in each solution for 15 and 30 minutes at 37°C. In order to evaluate remineralization effect, the VHN of the enamel surface was measured at every step by microhardness test (JTTOSHI INC, Japan). CLSM and SEM were utilized to identify the change of enamel surface. The pH of test solutions and VHN of enamel surface increased in proportion to the nano-HA concentrations (P<0.05). The nano-HA could reduce the erosive potential of a sports drink in a concentration dependent manner. These effects were confirmed by the CLSM and SEM images, which showed the remineralization effect of nano-HA. However, more study will be needed to examine the optimal concentration and remineralization mechanism of the nano-HA in sports drinks. In conclusion, the addition of nano-HA to a sports drink can promote enamel remineralization.

Abstract: The aim of this study is to reveal the response of highly malignant tumor cell to different hydroxyapatite particles. Human’s highly malignant melanoma (MM) cell line A875 is exposed to two kinds of short-rod hydroxyapatite particles. After incubated with hydroxyapatite particles at different time points, the effects of MM cell morphology, proliferation and invasion are evaluated by SEM, MTT, and MMP2 protein immunohistochemistry respectively. SEM figures show that superficial sentus of MM cells reduce; more secretion is found; and smaller HA particles have more obvious effect. At the same time, no statistic difference can be found in MTT assay and MMP2 expression measurement. This study also provides useful information about biosecurity of hydroxyapatite ceramic in transplantation after highly malignant tumor excision.

Abstract: Hydroxyapatite has high affinity rate with organic substance in an oral cavity, therefore lately nano-sized hydroxyapatite is extensively researched to increase affinity to tooth and remineralization. The objective of this research is indirectly to investigate the effect of nanohydroxyapatite on remineralization using valuation about whiteness and bacterial contamination of the bovine tooth. We have designed in vitro test for this purpose. The bovine teeth are sliced into human teeth size then the baseline whiteness of total 60 teeth is measured and assigned into 3 groups by cross-matching according to the whiteness. These samples were embedded into resin mold and underwent mechanical brushing during fixed schedule. The whiteness and bacterial contamination of teeth are measured and compared among 3 groups. Each dentifrice used in the experiment is composed of B.S.I group (30% Calcium Carbonate, precipitated-CaCo3) with abrasion rate of 100, Test Ⅰgroup (15% Sodium Metaphosphate, insoluble-NaPo3), Test Ⅱ group (15% Nano-hydroxyapate-Ca10(PO4)6(OH)2. After 20,000 strokes of mechanical brushing with each group sample teeth whiteness is measured for 2nd time and then the sample teeth were submerged into the same solution with oral bacteria for 10 days. The teeth whiteness is measured again for 3rd time and the bacteria from the surface of teeth are cultivated on agar badge for 3 days. We have compared with average of whiteness before and after test in group and each other 3 group. The whiteness of teeth was maintained in test group II, however in other group the whiteness achieved through brushing was lost. Also, Group II had the smallest area of bacterial colony on agar badge (p<0.01). It is concluded that the dentifrice including the nano-hydroxyapatite is replaced with the organic substance in enamel resulting the increase in whiteness and the resistance to bacterial colonization, which leads to the increase the enamel remineralization in teeth and result to decrease in caries susceptibility.