Key Engineering Materials Vols. 368-372

Abstract: Glass-alumina bi-layer composite was widely used as dental materials, the reliability and mechanical properties are very important for its practical application. In this work, residual stresses in dental glass-alumina composite and failure mechanism were investigated through finite element analysis and 3-point and ball-on-ring bending tests, respectively. The mechanical behavior of the dental material was studied using the bending tests and indentation method. Small bi-layer disk specimens were prepared for the axis-symmetrical tests using a set of small device in a universal tester. The results indicate that the difference in thermal expansion coefficients between two layers lead to residual stresses in both layers, and the stresses distribution depends on the thickness ratio and temperature difference. Furthermore, a proof testing method was proposed to estimate the workability and reliability of the dental ceramics.

Abstract: This study investigated the effect of multiple firing on the wear behavior of dental all-ceramic veneering ceramic (Cercon). Samples were fabricated according to the manufacturer's requirement for different firing times. The wear test was operated under simulated oral environment. The results showed that multiple firing could influence wear behavior of all-ceramic Veneer. Significant difference was observed in wear scar width among different samples. All the groups except 7time-firing one showed good wear resistance with low wear rate, smooth surface and relatively constant frictional coefficient. With the increasing firing times the wear scar width became larger. The wear resistance of dental ceramic after seven times firing was significantly lower. SEM/DFM results showed the wear facets of veneering ceramic demonstrate grooves characteristic of abrasive wear. The significant change was that severe wear dominated by brittle fracture could be seen in the 7time-firing group. Multiple firing can decrease the wear resistance of dental all-ceramic Veneer, and the wear pattern has the tendency to severe wear. The possible explanation is that the microstructure and properties of all-ceramic Veneering changed during multiple firing.

Abstract: The purpose of this study was to investigate the flexural strength and the mode of failure of dental colored ZrO2 ceramics with or without porcelain coating. Colorants (Fe2O3,CeO2, etc.) were mixed with 3Y-TZP powder to prepare colored dental zirconia. Specimens were made in monolithic or bilayered forms which were coated with veneering porcelain. Experimental results showed that there were not significantly differences of bending strengths between white and colored materials or between bilayered specimen, while the strength of monolithic specimen were significantly higher than their bilayered counterpart. In all bilayered specimens, the bulk fracture initiated at the tensile surface of the core material and was consistently accompanied with porcelain crush and delamination at the interface. Colorants for 3Y-TZP had minor effects on its mechanical properties.

Abstract: Partially sintered zirconia ceramics (PSZCs) for dental uses were prepared from zirconia nanopowder via isostatic pressing and partially sintering. The open porosities, pore diameters, grain sizes and mechanical properties of the ceramics with different densities were studied. The results show that the pores formed in the PSZCs are all open pores, with a diameter distribution of 60nm~130nm and a grain size distribution of 120~170nm. The machinability becomes worse when the density of PSZC is higher than 75% of the theoretical density, so a ceramic named PSZC-70% with density of 70%TD was selected as the target material. Its bending strength is 168 MPa and fracture toughness is 1.8 MPa·m1/2. A dental restoration framework can be obtained via machining the PSZC-70% on a dental CAD/CAM system.

Abstract: This paper explored the color and mechanical properties of CeO2 and Er2O3 shaded zirconia ceramics for dental application. Twelve kinds of colored dental ZrO2 powders were prepared. Experimental results showed that the hue of the materials shift from yellow-green to yellow-red with the increasing concentration of the CeO2 and Er2O3, while reducing of the brightness( L* ) value was little. Three-point bending strength decreased form 1209MPa to 845MPa after coloring, which was lower than the uncolored materials (1301MPa). The fracture toughness decrease slightly. SEM observation revealed more porous microstructure in specimen containing both two additives. Cerium oxide and erbium oxide are candidates of color additives for shading dental zirconia ceramics.

Abstract: This study was conducted to evaluate shear bond strength between self-made alumina glass composites (AGC), zirconia glass composites (ZGC) and Vita alpha opaque-dentine porcelain, and also evaluate the effects of different surface treating methods on the bond strength. The AGC and ZGC specimens were treated differently and then bonded with Vita alpha opaque-dentine porcelain. The bond strength was measured by shear test and the surface treating methods included no-treatment, sandblasting and etching. The results showed that the values of bond strength for AGC groups were 30.1, 41.1 and 41.9 MPa respectively, and the bond strength of both sandblasting group and etching group were significantly higher than that of the untreated group; the bond strength of ZGC groups were 60.2, 63.6 and 35.5MPa respectively, and the value of sandblasting group was significantly higher while etching group was lower than that of untreated group. These results indicated that Vita alpha opaque-dentine porcelain can be well sintered to self-made AGC and ZGC. Sandblasting can greatly improve the bond strength for both AGC and ZGC, while the etching treating method had different effect on their bond strengths.

Abstract: This study sought to compare the biocompatibility of four dental ceramics so as to provide indications useful for the further development of dental materials. Osteoblasts were obtained by culturing the cranial explant of SD rat and cultured in vitro when they were seeded onto four different materials: hydroxyapatite, bioactive glass ceramics, tricalciumphosphate-hydroxyapatite and nano-hydroxyapatite (nHA). The phase contrast microscope and scanning electron microscope were used to evaluate the cell morphology and attachment. The content of alkaline phosphatase was calculated by molecular biological methods. MTT method was performed to find the alteration of proliferation. Then by use of wash way method, the adhesion ability was tested. The results showed that all of the four bioceramics had good cytocompatibility. There were significant differences among them on the levels of cell growth, differation and adhesion in vitro. The biocompatibility of nHA is the best and of conventional HA is the worst.

Abstract: HA/ß-TCP is one kind of important bone tissue engineering scaffold materials. In order to improve the biological performance of materials, HA/ß-TCP ceramics were modified by the cold plasma technique in this paper. The biological performances of treated materials were evaluated by the results of bone-like apatite formation in SBF, the coculture of the C2C12 cell line and HA/ß-TCP, cell proliferation experiments, observations of the electron microscopy and fluorescence staining and the animal intramuscular implantation experiments. The results showed that after immersion, compared with untreated HA/ß-TCP, treated materials were more conducive to form bone-like apatite; modified HA/ß-TCP could promote the cell proliferation more; the cells grew in the course of nature on the treated scaffold and modified HA/ß-TCP had better bone-forming performance in vivo. It was concluded that modified HA/ß-TCP had better biological performance; the cold plasma technique could improve the biological performance of dental biphasic calcium phosphate ceramics.

Abstract: The aim of this investigation is to study the effect of SnO coatings on the bond strength between titanium and porcelain. The coatings were produced by sol-gel method and heat-treatment at 300°C. Once the coatings have been formed on the titanium substrates, self-made porcelain was fused. The specimens with pre-oxidation before porcelain fused were set as control group. It was shown SnO gel formed completely at 300°C and was composed by SnO and SnO2 in the form of a uniform film. The bond strength between titanium and porcelain of the specimens with SnO coatings was greater than those in control group statistically, which might prove that the coatings reduced the oxidation of titanium surface in the porcelain fusing progress. EDS result showed almost all fractures between titanium and porcelain occurred at the oxide layer. Si and Sn might attend the reaction at interface. It was concluded that the SnO coatings produced in this study can improved the titanium-porcelain bond strength.

Abstract: Ceramic oxidation coating of approximately 60 m thick was prepared on a Ly12 alloy substrate by micro-plasma oxidation in an alkali-silicate electrolytic solution. Coating thickness was measured during coating formation. The influence of current density, electrolyte temperature and inter-electrode distance on coating kinetics was investigated. Microstructure and phase compositions were analyzed. The micro-hardness of the coating was also measured. The tribological performance of the coatings was evaluated using a dry sand abrasion test. In addition, the results are compared to detonationsprayed alumina coating.