Papers by Author: Chen Wang

Abstract: Established two-dimensional axisymmetric staggered tooth shape labyrinth seal grid model by GAMBIT software, simulated oil-air two-phase mixture flow field within labyrinth seal by fluent software, confirmed the best grid size of numerical calculation, studied the seal mechanism and influence of gap width variation on the leakage. The results show that when fluid flows through the narrow clearance, its velocity increases and pressure decreases. The optimized clearance width within 0.5mm to 1.0mm is preferable.

Abstract: Irradiation crosslinking is one of the most important methods to modify UHMWPE, it can effectively improve the hardness, creep resistance and abrasion resistance of this material. In order to eliminate free radical, increase material strength, abrasion resistance and fatigue resistance of creep, this study uses Co60-γ to modify UHMWPE under vacuum atmosphere, with the irradiation dose of 30, 60, 90, 120 Kgy respectively. Its mechanical properties, microstructure, degree of crosslinking and crystallinity are analyzed, the results show that the modified UHMWPEs impact strength decreased, elongation basically remain unchanged, tensile fracture strength and tensile yield strength increased.

Abstract: A novel microsphere scaffolds composed of chitosan and β-TCP containing vancomycin was designed and prepared. The β-TCP/chitosan composite microspheres were prepared by solid-in-water-in-oil (s/w/o) emulsion cross-linking method with or without pre-cross-linking process. The mode of vancomycin maintaining in the β-TCP/chitosan composite microspheres was detected by Fourier transform infrared spectroscopy (FTIR). The in vitro release curve of vancomycin in simulated body fluid (SBF) was estimated. The results revealed that the pre-cross-linking prepared microspheres possessed higher loading efficiency (LE) and encapsulation efficiency (EE) especially decreasing the previous burst mass of vancomycin in incipient release. These composite microspheres got excellent sphere and well surface roughness in morphology. Vancomycin was encapsulated in composite microspheres through absorption and cross-linking. While in-vitro release curves illustrated that vancomycin release depond on diffusing firstly and then on the degradation ratio later. The microspheres loading with vancomycin would be to restore bone defect, meanwhile to inhibit bacterium proliferation. These bioactive, degradable composite microspheres have potential applications in 3D tissue engineering of bone and other tissues in vitro and in vivo.

Abstract: Bone tissue engineering provides a new way to repair the bone defect in orthopaedics. The scaffolds, porous materials with excellent biocompatibility, bioactivity and biodegradability, play an important role in bone tissue engineering. Furthermore, the bioactivity of the pore interior surfaces is very important for cell attachment, differentiation and growth, as well as new bone tissue ingrowth into pores. In this paper, β-TCP was selected as materials of scaffolds, and its bioactivity was improved by activating the interior surfaces of pore walls. The porous β-TCP scaffolds with about 50~300μm of pore size and above 80% of porosity were obtained by 3D-gel-laminated processing. Their surfaces of the scaffolds were easily covered by a low crystallized bone-like apatite layer, which determined by XRD and FTIR, after immersing in 1.5SBF solution following pre-treatment by NaOH solution. MTT and ALP assays were performed after cells cultured on the porous scaffolds with bone-like structure, and the results showed higher proliferation rate and differentiation level than that on the scaffolds without treatment, which indicated that the porous β-TCP scaffolds with bone-like apatite layer on surfaces of pore walls possess higher bioactivity. Therefore, the bioactivity of tissue engineering scaffolds could be improved by deposited bone-like apatite layer on their surfaces.

Abstract: The purpose of this study was to study effects of the mechanical properties of veneering porcelain on stress distribution of dental zirconia layered structure by three-dimensional finite element analysis. A 3-D geometric model of the first maxillary molar was established, a tooth preparation was simulated by the Imageware software. A crown was designed and divided into three layers: core, middle layer and outer veneer layer. The elasticity modulus of the middle layer was 70GPa for the control model up to 175GPa for the tested models. Loads of 200N were applied over a 1 mm diameter area beneath the tip of the mesial-distal cusp, simulating typical occlusal contact areas, the stress distribution of the crown systems were analyzed. Results show that within the geometry of the crown configuration, one concentration district of maximum principal stress occurred on the occlusal surface closely proximal to the loading position, several sub-maximum principal stress area were observed, such as margin regions of the mesial face, lingual face, distal faces, buccal face and occlusal fossa. Middle layer with higher modulus can effectively disperse the stress concentration in the layered zirconia all-ceramic crown system.

Abstract: Low temperature aging (LTD) is an important factor of Y-TZP ceramic as artificial joint femoral head and dental restorative materials in vivo for long-term application. In this paper, the accelerated aging experiments on Y-TZP ceramics were conducted. The t-m phase transition is occurring from the surface to the inside during low temperature aging of Y-TZP ceramics. As content of phase transformation increases, thickness of phase transformation layer increases. While the content of surface monoclinic phase is less, the volume expansion and surface stress caused by phase transformation can make cracks and holes shrink or even close, then the flexural strength increase. As a large number of surface monoclinic phase was generated, due to there are a lot of microscopic defects in the phase transition layer, crystals loose, strength of grain boundary lower than that of not aging area and phase transformation layers fracture in the intergranular mode, that damages the flexural strength. Therefore, the flexural strength increase firstly and then decrease with the increase of surface monoclinic content.

Abstract: The matching properties of ceramics and veneering porcelain play an important role for the overall color and mechanical properties of dental crowns. The Vita VM9 veneering porcelain was coated on the surfaces of two zirconia, three-point flexural strength, heat shock resistance and the overall color after veneered with porcelain were tested. The results showed that the interlayer cracks, radial cracks or porcelain body cracks were not appeared in all samples during thermal shock experiments at 60~220°C. Their flexural strength was all above 700MPa and the overall color covered the common color of VITA-3D Master shade guide. There is good thermal compatibility between the two dental shaded zirconia ceramics and Vita VM9 veneering porcelain. The mechanical properties are suitable for clinical posterior teeth area restorative, and the overall color is also suitable for the requirements on the color and brightness of clinical dental restoration.

Abstract: The purpose of this study was to investigate the structure, mechanical and low temperature aging properties of colored dental zirconia ceramics. Colored 3Y-TZP zirconia dental zirconia ceramics were made by mixing colorants and their combinations into a 3Y-TZP powder, the green body were compacted at 200MPa, presinter at 1050°C and densely sintered at 1500°C for 2h. Specimens were subjected to an accelerated aging test carried out in an autoclave in steam at 134°C, 2bar, for 4hs. XRD was used to identify the crystal phases, three-point bending strength were tested before and after aging according to the ISO 6872 standard, polished and aging specimens were observed by Atomic Force Microscopy (AFM) to evaluate surface microstructure. Tetragonal-to-monoclinic phase transformation was detected for both uncolored and colored specimens, the relative content of monoclinic phase was increased with the prolonged aging time. Aging had no significant negative effects on flexural strength on colored 3Y-TZP. The nucleation and growth of monoclinic phase were detected by AFM in surface of both colored and uncolored zirconia.

Abstract: The purpose of this study was to investigate the effect of different veneering porcelain types on the flexural strength of dental Y-TZP/porcelain layered structure. KAVO™ Everest zirconia ceramics were selected as substructure. To forming Y-TZP/porcelain bilayered structure, a leucite based veneering porcelain was fired on the zirconia substructures by slip-casting technique with dentin washbake, and two nano-fluorapatite based veneering porcelain was fired on the zirconia substructures either by slip-casting or pressed-on technique with or without liner coverage. Bending strength was tested according to ISO 6872 standard, and the veneered surfaces of fracture samples were analyzed by SEM. Experimental results showed that for covering KaVo™ zirconia core material, conventionally applied veneering slurry-porcelain combined with liner or wash firing has significant higher bending strength than pressed-on porcelain. SEM showed that the main failure type at the interface was adhesive.

Abstract: The purpose of this study was to investigate the effect of pigmentation on the flexural strength of dental Y-TZP/porcelain layered structure. KaVo™ Everest zirconia substructures was pigmented by dipping presintered blocks in coloring solution, and colored TZ-3YS zirconia substructures were fabricated by adding pigments before isostatically pressing. Specimens were made in monolithic or bilayered forms. The bending strength was tested. XRD and SEM with EDX were used to analyze the characteristics of the surface structure. Experimental results showed that there were significant differences of bending strength in both zirconia systems between white and colored monoclinic materials, which also in bilayered structures. Pigmentation has no apparent effects on the bonding strength between veneering porcelain and zirconia. Both coloring methods are appropriate when the concentration of pigments is under deliberate controlled.