Key Engineering Materials Vols. 529-530

Abstract: Calcium phosphate (CaP) material has been used successfully for protein delivery. In the present work, our aim is the preparation of CaP combined with peptide and protein, and is the evaluation of pH-sensitive drug release ability. Protein used as the model drug was fluorescein isothiocyanate-bovine serum albumin (FITC-BSA). All compounds synthesized were low crystalline hydroxyapatite (HAp). The result of zeta potential indicated that incorporation of peptide in HAp could be changed the surface charge of particle. The CaP-BSA and CaP-BSA-pLys [Poly-L-lysine (pLys) was added to CaP composite.] were-23.1 mV and-12.0 mV, respectively. The ratio of protein release and dissolved Ca ion were measured by soaking CaP-peptide composites under various pH (pH 7.4, pH 6 and pH 5) conditions. BSA was released from CaP-BSA-pLys at only pH 5, not at pH 7.4 and pH 6.

Abstract: Calcium phosphate (CaP) coating is an effective technique for surface functionalization of biomaterials. The objective of our research is to prepare calcium phosphate (CaP) coatings on a hydroxyapatite/collagen (HAp/Col) nanocomposite and subsequently provide it with gene delivery function through the immobilization of DNA in the coating. We have specifically selected the HAp/Col nanocomposite since it has the high potential as bone substitutes due to its similar composition, nanostructure, and biological properties to those of human bone. CaP coatings consisting of different sized particles were prepared on the HAp/Col nanocomposite membrane by immersing it in supersaturaterd CaP solutions (so-called RKM solutions) with the varied Ca and P concentration levels. We immobilized DNA in the CaP coatings together with lipid and fibronectin by supplementing DNA, lipid, and fibronectin to the RKM solutions (DLF-RKM solutions). Gene transfer capability of the resulting HAp/Col nanocomposite membrane was improved with decreasing concentration level of the DLF-RKM solution. It was confirmed that the present CaP coating technique was effective in providing the HAp/Col nanocomposite membrane with gene transfer capability and that the Ca and P concentration level of the DLF-RKM solution was a controlling factor affecting the gene transfer efficiency.

Abstract: The effect of structure and composition of calcium phosphate (CaP) nanoparticles namely hydroxyapatite (HA), calcium deficient hydroxyapatite (CDHA) with Ca/P ratio ranging from 1.33 to 1.61 and tricalcium phosphate (β-TCP), on the efficiency of nanoparticles as an ideal drug carrier have been investigated. Ibuprofen, an anti-inflammatory drug was chosen for this study. The CaP nanoparticles were prepared by microwave accelerated wet chemical synthesis method and were characterized by X-ray powder diffraction, infrared spectroscopy, and electron microscopic techniques. The loading and release profiles of ibuprofen from the nanocarriers was studied using UV-Vis spectroscopy. Maximum loading of the drug was observed in β-TCP (75%) followed by CDHA of Ca/P ratio 1.5. Both samples have same Ca/P ratio but have different crystal structure. Low amount of drug loading was observed in HA and other CDHAs which have Ca/P ratio different from 1.5. Although, all the samples exhibits sustained release of ibuprofen for about 7 days, the maximum release was also shown by β-TCP (26%). Among HA and CDHAs, the amount of ibuprofen release increases with increasing Ca/P ratio. The loading and release profile of ibuprofen drug seems to be strongly related to the Ca/P ratio and structure of CaP nanocarriers.

Abstract: Three kinds of dental zirconia (Cercon, NANOZR, and P-NANOZR) were ground and polished with seven kinds of clinical device and materials. After these grinding and polishing, the surface roughness and the glossiness were analyzed. The crystal phases of the surface were analyzed with a micro X-ray diffractometer. The results demonstrated that all three zirconia showed the smallest roughness and the highest glossiness when they were polished with diamond-containing polishing pastes. Tetragonal to rhombohedral transformation was observed on the ground and polished surfaces of Cercon and ZENOSTAR, whereas monoclinic phase was also detected on the ground and polished surface of P-NANOZR. The polishing with diamond-containing pastes showed the smallest transformation amount of rhombohedral and monoclinic phases. It is concluded that dental zirconia can be well polished with diamond-containing pastes, and the phase transformation are also reduced.

Abstract: The bond strengths between two kinds of zirconia and three kinds of feldspathic veneering porcelains were measured. The specimens were prepared at four firing temperatures for three holding periods, respective opaque porcelain was painted and vacuum-fired. Then, each dentin porcelain was condensed in an acrylic resin mold and vacuum-fired under the conditions mentioned above. Cross sections of the interface between zirconia and porcelain were observed with a scanning electron microscope. The specimens were fixed to specimen holder on a universal testing machine. Data of the bonding test were statistically analyzed. The results showed that all the four factors statistically affected the bonding strength (p<0.01). The contribution of the firing temperature was highest and that of the porcelain type was lowest (p<0.01).

Abstract: A composite resin (CR) with photo-polymerization is widely used for dental filling material. Because of their good esthetics, the visual inspection of restored teeth becomes difficult. In this study, the fluorescent glass/ceramics fillers containing rare earth oxides — which are well-known fluorescent materials — was prepared and applied in CR to enhance visual inspection capability with small influence in color. Eu₂O₃-containing Y₂O₃ filler (Y₂O₃:Eu) prepared with homogeneous coprecipitaion method showed clear fluorescence at 614nm with near ultraviolet light (385nm) excitation. The fluorescence intensity of the prepared Y₂O₃:Eu filler increased with increase of Eu content in the Y₂O₃ filler upto 15mol% of Eu content. The composite resin was prepared with the mixed filler of Y₂O₃:Eu filler and the conventional glass filler. The content of Y₂O₃:Eu was varied between 0 to 40wt% of mixed filler. The prepared composite resin also showed clear fluorescence with quite small affect to the color change and the Vickers hardness of composite resin. Therefore, the prepared rare earth oxide containing Y₂O₃ filler was applicable as the filler of dental composite resin.

Abstract: A biodegradable material that bonds to hard tissues such as bones and teeth is urgently needed for medical and dental applications. However, such materials are not available in today’s clinical practice of orthopedics and dentistry. Therefore, we synthesized biodegradable phosphorylated pullulan to develop a biomaterial that combines primary properties such as high biocompatibility, good bonding potential to hard tissue, high strength, biodegradability, and osteoconductivity. The pharmacopoeial polysaccharide pullulan was chemically functionalized with dihydrogen phosphate groups. Phosphorylated pullulan was formed network by adding calcium ion, making the composite less soluble in water. Adhesive force measurement revealed that adhesiveness of the pastes before setting can be controlled through optimization of additives. In addition, histological evaluation revealed that phosphorylated pullulan-based composite possesses high biocompatibility. These results indicate that phosphorylated pullulan can be used as a key material for regeneration and reconstruction of bone and tooth.

Abstract: Tooth enamel cannot be reconstructed once it is destroyed immoderately. Hydroxyapatite (HAp) thin sheet can potentially be used for a novel dental biomaterial to repair the enamel. Using a pulsed laser deposition (PLD) method, we have successfully created a flexible HAp sheet of less than a few micrometers in thickness. Due to its flexibility, the HAp sheet is tightly adhered on curved surfaces at the target site. In the present study, we newly developed double-layered sheets composed of HAp film coated with tricalcium phosphate (TCP) thin layer. The HAp/TCP sheet was adhered to the extracted human teeth using a calcium phosphate solution for 3 days. The adhesive strength between the HAp/TCP sheet and tooth enamel was evaluated by quasi-static tensile tests. Moreover, the interface structure between them was observed by a scanning electron microscopy. As a result of the mechanical evaluation, the adhesive strength was greater than approximately 2.5 MPa. The electron microscopic observation revealed that the sheet was partially fused with the enamel. These findings suggest the possibility that enamel defects are repaired using the HAp/TCP sheet for a short duration.

Abstract: Ammonium hexafluorosilicate [SiF: (NH₄)₂SiF₆] solution was prepared in order to overcome the tooth discoloration caused by diamine silver fluoride [AgF: (NH₃)₂AgF] application. However, it is still unclear how the concentration of SiF solution affects the crystallinity of enamel. The aim of this study was to evaluate the effects of changing concentrations of SiF solution on the crystallinity of hydroxyapatite powder and structure of human enamel. Hydroxyapatite powder was treated with several concentrations of SiF solution (from 10 to 19,400 ppm) for five min. The crystallinity of hydroxyapatite powder before and after SiF treatment was then measured by powder X-ray diffraction (XRD) analysis. The angular width (β) of the 002 diffraction peak was measured at 1/2 the height of the maximum intensity. Also, enamel specimens were prepared from a human extracted tooth. Several concentrations of SiF solution were applied to polished or phosphoric acid etched enamel specimens. The enamel surface was then observed using scanning electron microscopy (SEM). XRD peaks became sharper after SiF treatment indicating that the crystallinity of apatite powder was increased. The 1/β value was increased from 2.8±0.1 to 4.3±0.1 after treatment with 1,000 ppm SiF solution. The amount of CaF₂ formed in hydroxyapatite powder was gradually increased with increasing concentrations of SiF solution. The XRD pattern was consistent with CaF₂ in case of over 9,000 ppm SiF solution. SEM photographs demonstrated that exposed enamel rods with acid etching were filled with CaF₂-like precipitate after SiF treatment regardless of the concentration of SiF solution. It was concluded that SiF treatment increased the crystallinity of apatite powder and repaired the demineralized enamel surface with the formation of CaF₂ or CaF₂-like precipitate, and thus, SiF treatment would be useful for the prevention of dental caries.

Abstract: Calcium phosphate/ titanium oxide/ titanium/ plastic composite implants with 1.6-mm diameter and 7-mm length were successfully formed using a DC/ RF magnetron sputtering machine. The sample had no cracks and the surface of the sample was uniformly smooth. The chemical composition of the >10-nm-thick calcium phosphate layer was Ca: P: O=1.0: 0.79: 2.8. The sample was implanted into the tibia of an male 8-week-old SD rat for 28 days. When 0.70-μm sections of the tibia were prepared, the titanium layer with titanium oxide layer of the implant was not broken and the surfaces of the layer of the implant had not decomposed. The interaction between living bone and the implant could be clearly observed by light microscope and TEM.