Key Engineering Materials Vols. 309-311

Abstract: Hydroxyapatite is the main component of enamel that gives the tooth a bright white appearance and eliminates the diffused reflection of light by filling up the fine pores of the tooth surface. Accordingly, remineralization of the teeth can be expected to some extent if hydroxyapatite is used to treat an incipient caries lesion (early white spot lesion). In addition, the remineralization effect will be increased if the particle size of hydroxyapatite can be reduced to less than that of the micron-size in existing toothpaste preparations. The aim of this in vitro study was to evaluate the effect of nano-hydroxyapatite toothpaste, which was produced by nano-technology, on the remineralization of human enamel. A tooth specimen, on which artificial incipient caries had been induced, was immersed into two toothpaste slurries for remineralization. One contains nano-sized hydroxyapatite and fluoride, and the other contains nano-sized hydroxyapatite excluding fluoride. In order to evaluate the remineralization effect, the Vickers Hardness Number & SEM image of the enamel surface was evaluated at each step. There were significant differences in VHN values between those obtained before and after the remineralization steps. The results showed that the remineralization effect increased with increasing immersing time (P<0.05). However, there were no significant differences in VHN values between the two groups (P>0.05). SEM also demonstrated differences the in micro surface at each step. In conclusion, a toothpaste containing nano-sized hydroxyapatite has the potential to remineralize an incipient caries lesion. In addition, the addition of fluoride had no synergistic effect on remineralization.

Abstract: The aim of this in vitro study was to evaluate the tooth whitening effect of toothpaste containing nano-sized hydroxyapatite (HA). There were 3 types of dentifrices, which had a different level of abrasive components. For group 1, a newly developed toothpaste containing Nano-sized hydroxyapatite (Nano-HA) was used. Commercially available toothpastes were used in groups 2 and 3. Group 2 used toothpastes containing silica and multi phosphate. Group 3 used toothpastes containing abrasives with silica and micro-sized HA. In order to simulate 6-months of tooth brushing, the tooth specimens in all 3 groups were placed on a V8 Cross Brushing Machine (Sabri Co. U.S.A.) and brushed 10,000 times with the toothpaste slurries. The tooth specimens were then soaked in artificial saliva for 24 hours to create conditions similar to those encountered in vivo. The whitening efficacy was assessed before and after tooth brushing using the VITA shade scores of Shadeeye-EX NCC Dental Chroma meter (Shofu Co. Japan). All toothpastes produced significant differences in the mean shade change in the teeth before and after tooth brushing (p<0.05). However, there were no significant differences in the change in the shade between each group (p>0.05). Although the new Nano-HA toothpaste did not have superior whitening effects to the commercially available whitening toothpastes, they had a similar whitening efficacy to commercially available whitening toothpastes. These effects might come from the physical properties of Nano HA, which increase the surface dimension more than the Micro-sized HA and have the potential of remineralization.

Abstract: Synthetic model of a large transparent crack-free monolithic ceramic-polymer hybrid, which was synthesized using triethoxysilane end-capped poly(tetramethylene oxide) (Si-PTMO) and tetraethoxysilane (TEOS), was examined in the CaO-SiO2-PTMO sol-gel system. Bulk precursor with nominal mass ratio of PTMO: TEOS = 80: 20 and surface precursor with nominal molar ratio of TEOS: Ca(NO3)2 = 1: 0.3 were subjected to hybridization through hydrolysis and condensation process, producing a bi-structured hybrid in which polymeric bulk was molecular hybridized with bioactive silicate surface. Spectroscopic and microscopic characterizations revealed that the surface of hybrid was typical bioactive silicate. In vitro study using a simulated body fluid (SBF) revealed that the hybrid formed an apatite on its surface within 6 hours in SBF, suggesting bioactive materials with high capability of tissue integration as well as polymeric physical properties.

Abstract: Nano-sized hydroxyapatite (HA) chloroform suspensions were firstly prepared by reactions in an emulsion system of Ca(OH)2-H3PO4-chloroform-lecithin, then, HA/PMMA composites with well dispersed HA could be obtained by adding PMMA into the suspension. The residual water in the HA suspension could lead to a porous surface which demonstrated better bioactivity in in vitro test. The residual water could cause HA particles to exist on pore walls during the composite formation, resulting in the increase of the HA amount per unit surfac

Abstract: Ceramic-polymer bi-structured nano-hybrid, in which the bioactive silicate surface is nano-hybridized with flexible polymeric bulk, was synthesized in the tetraethoxysilane (TEOS)-polydimethylsiloxane (PDMS) sol-gel system. Different solutions for surface and bulk, whose compositions of TEOS: PDMS were respectively fixed 100: 0 and varied from 50: 50 to 20: 80 with various molecular weight (Mw) of PDMS, were subjected to lamination and controlled polymerization and condensation process, producing a large transparent crack-free monolithic bulk. Characterizations at near-surface cross-section of the bi-structured hybrids revealed that typical bioactive silicate was combined with all types of bulk hybrids regardless of their PDMS contents and Mw without distinct interface, indicating possibility of a novel bioactive nano-composite with enhanced physical and biological functions.

Abstract: Hydroxyapatite/hyaluronic acid (HAp/HyA) and hydroxyapatite/chondroitin sulfate (HAp/ChS) microparticles, which show the high adsorption ability of proteins, high biocompatibility and osteoconductivity, are potential scaffolds for a time-controlled BMP release. The present study evaluated the biocompatibility and osteoconductivity of the composites after injection into bone defect. Drilled bone holes were made at tibia and femur of Japanese white rabbits, and HAp/HyA or HAp/ChS was implanted into each bone hole using an injection syringe. After 2 and 4 weeks of implantation, rabbits were sacrificed and histological observations were conducted with HE, TRAP, and ALP staining. Histological observations revealed that HAp/ChS has superior biocompatibility compared with HAp/HyA, and 20% HAp/ChS promotes bone formation as well as osteoblast activities compared with lower ratios of HAp/ChS.

Abstract: Nano-sized zinc containing β-tricalcium phosphate (ZnTCP) powders were synthesized by a co-precipitation method. The co-precipitation took place in an ice-water bathed beaker, after further washing, freezing, lyophilizing and calcining at 800°C, the precipitates transformed to ZnTCP powders. The XRD pattern of the ZnTCP powders demonstrated a pure β-TCP phase. TEM observation revealed the particle size is about 100-120nm, which is favorable for TCP particles to form composites, such as polymer based composite, and as well to attain a desired microstructure. It was found zinc incorporation could eventually result in the decrease of particle size, thus be beneficial for its further application.

Abstract: Previous study showed that the novel poly(ε-caprolactone)–organosiloxane nano-hybrid material (SiOPCL) had bioactivity, biodegradability, and mechanical properties comparable to those of human cancellous bone. In this study, hydroxyl carbonate apatite layer (HCA) was preformed on the surface of SiOPCL, which mimicked the events likely to occur in vivo, and cellular behaviors of human bone marrow stromal cells (hBMSCs) were investigated during the osteogenic differentiation on its surface (SiOPCL/HCA). Initial attachment, proliferation, and ALP activities of hBMSCs were comparable to those on tissue culture plates (TCPs), while the calcium content in the cell layer showed significantly higher value. It means that this novel bioactive nano-hybrid material is likely to be a promising candidate for bone grafting materials because of good hBMSCs responses as well as apatite forming ability in the simulated body fluid.