Key Engineering Materials Vols. 512-515

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: Aim To explore pigmented glass for infiltration and investigate its physical and mechanical properties. Methods The pigmented glass was prepared by melting glass components in an alumina crucible at 1400°C for 2h. The thermal properties were tested using a Setaram-TGDTA 92 analyzer; three point bending strength and fracture toughness were also tested; the microstructure of the glass was studied using a scanning electron microscope. Results The thermal expansion coefficient over the range 20–600 °C was 6.2 × 10-6 °C -1, Tg was about 690 °C, the density, bending strength, fracture toughness and Vickers hardness were 2.23 g/cm3, 118 MPa, 1.22 MPam1/2, and 7.4 GPa respectively. Conclusion The pigments have no detrimental effects on the physical and mechanical properties; thus the pigmented glass for infiltration has favorable physical and mechanical properties and also good compatibility with presintered porous alumina.

Abstract: Our aim was to analyze the color ranges of two kinds of Vita shade guides and compare these color ranges with that of Chinese teeth. To do this, the color range and ordering of the Vita Classical and Vita 3D-Master shade guides were measured and analyzed with a MINOLTA CM-2600d spectrophotometer under a D65 standard source. The CIE-1976-L* a* b* system was adopted. We found that compared with the Vita Classical shade guide, Vita 3D Master covers a greater range of a*, and b*, which includes more yellow -reddish and more saturated color tabs. The range of L* extends further towards darker values, while in higher range the two guides are the same. Comparing these color ranges with that of Chinese teeth, the Vita 3D-Master is preferred to the Vita Classical Guide. Because of the larger range of teeth-colors covered, and the logical arrangement, we recommend the clinical use of the Vita 3D-Master shade guide.

Abstract: Recently magnesium (Mg) alloys were widely studied as biodegradable implants for orthopedic applications duo to their suitable mechanical and biological properties. However, too fast degradation rate of Mg alloys would cause potential harm to human body. With the aim to promote the corrosion resistance of Mg alloys, mesoporous hydroxyapatite (meso-HA) coatings were synthesized on the AZ31 Mg alloys by dipped into meso-HA sol for different times (1, 3, 5 times, respectively) and subsequently heat treated. The morphologies of naked and coated samples were investigated by scanning electron microscopy (SEM). The whole surface of AZ31 Mg alloys was fully covered by a uniform coating consisted of spherical meso-HA particles sized in ~50 nm after being dipped into the meso-HA sol for 5 times. To evaluate the corrosion properties of naked and coated samples, immersion tests and electrochemistry measurement were carried out in phosphate buffer solution (PBS) at 37 °C. After the immersion of 3 days, the average corrosion rate of coated samples was calculated to be 8.7×10^-3 mm/d, suggesting a greater corrosion resistance than the naked ones (8.1×10^-2 mm/d). All the results indicated that it is a potential approach to improve the corrosion resistance Mg alloys with meso-HA coatings.

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: 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: Silicon coatings were prepared by vacuum plasma spraying (VPS) and air plasma spraying (APS) technologies. The samples were hydrothermally treated and then incubated in simulated body fluid (SBF) to evaluate their bioactivity and silicon wafer was used as control sample at the same time. The SBF test showed that a Ca-P layer was formed on the surface of silicon wafer and VPS-Si coating after immersion in SBF for certain time, indicating their improved bioactivity. Whereas no Ca-P layer was found on the surface of APS-Si coating. The results of X-ray photoelectron spectroscopy showed that the Si/O atomic ratio and chemical depth profiles of the silicon oxide films on the surface of silicon wafer, VPS-Si and APS-Si coatings were different. The results indicated that the bioactivity difference of silicon-based material resulted from the different composition of their surface. Hydrothermal treatment maybe a favorable method to improve the bioactivity of silicon-based material having silicon oxide of non-stoichiometric Si/O atomic ratio.