Papers by Author: Hong Chen Liu

Abstract: To study the influence of background color to 3 all-ceramic system core materials.The chromaticity value of all samples that were put on noble metal, Ni-Cr alloy, Hg-Ag alloy and resign background were measured with chromatism instrument, and chromatic aberration among groups were calculated. The chromatic aberration of Empress II samples on different background color could be distinguished by human eyes, but those of Alumina and Zirconium were unable to being distinguished. In conclusion, the influence of background color to Empress II and In-Ceram Alumina of AL1 were lager. When chosen as core material, noble metals should be covered to keep prosthesis from clinical color-transform. As background to In-Ceram Alumina of AL2, it was unnecessary for resin to be covered. In-Ceram Alumina of AL3, AL4 and In-Ceram Zirconium weren’t affected by background color.

Abstract: The present paper probes into the effect of background color of different post-core materials on the core materials of In-Ceram AL2 Electroformed Alumina, Z21 Electroformed Zirconia, Cercon base color Zirconia, and Cercon base Zirconia. The spectrocolorimeter was used to measure colorimetric values of all groups of samples against the background of noble metal, nickel-chromium alloy, silver amalgam and resin, and to calculate the color difference among the groups. The result showed that the color difference of Cercon base color Zirconia viewed against different backgrounds was identifiable by human eyes (ΔE > 1.5). In contrast, the color differences of In-Ceram AL2 Electroformed Alumina, Z21 Electroformed Zirconia and Cercon base Zirconia viewed against different backgrounds were unidentifiable by human eyes (ΔE < 1.5). Based on this, it can be stated that Cercon base color Zirconia is significantly affected by background color. Thus, proper method to shelter the background color should be adopted. In addition, AL2 Electroformed Alumina, Z21 Electroformed Zirconia, and Cercon base color Zirconia are less influenced by the background color, thus it is not necessary to cover the background color.

Abstract: The spectral transmittance of six kinds of Vita In-Ceram and Cercon all-ceramic core materials after veneering ceramic was determined. Based on the production method recommended by the manufacturer, specimens of the same thickness are made. PERKIN ELMER Spectrophotometer is adopted to measure the spectral transmittance of In-Ceram AL2 slip-casting glass/alumina composite, AL2 electroformed alumina, Z21 slip-casting glass/zirconia composite, Z21 electroformed zirconia, Cercon base color zirconia and Cercon base zirconia all-ceramic core materials, after veneering ceramic. The results show that, after veneering ceramic, Cercon base Zirconia has the highest spectral transmittance, followed by AL2 Electroformed Alumina and Z21 Electroformed Zirconia, whereas the transmittance of Z21 slip-casting Glass/Zirconia composite has the lowest. Statistical data show that, among the groups, In-Ceram slip-casting Glass/Alumina composite (AL2), Electroformed Alumina (AL2), Cercon base color Zirconia and Cercon base Zirconia have significant differences between every group. On the other hand, there is no significant difference between In-Ceram slip-casting Glass/Zirconia composite (Z21) and Electroformed Zirconia (Z21). Therefore, we should choose all-ceramic restoration materials based on the spectral transmittance of all-ceramic core materials after veneering ceramic and transparency of the remaining natural teeth of patients.

Abstract: Objective: To investigate the effects of different surface treatments on the microstructural and crystallographic changes of dental 3Y-TZP ceramics. Methods: 21 pieces of zirconia specimens (15 ´ 15 ´ 1.5 mm) were prepared and divided into 7 groups: control group; grinding group; polishing group; sandblasting group; sandblasting + veneer porcelain sintering group; sandblasting + veneer porcelain sintering twice group and sandblasting + annealing group. The crystal structure of specimen was monitored by X-ray diffraction (XRD) before morphological observation with scanning electron microscope. Results: monoclinic phase increased after grinding while decreased little after polishing, bigger phase change presented after sandblasting compared with decreased phase change induced by veneer porcelain sintering; annealing eradicated the surface m phase. Grinding produced coarse scratches on the surface of samples with removal of surface particles; after grinding and polishing to 7 um level, the surface particles were removed massively, and the surface became smooth with remaining scare scratches and substantial micro cracks. Sandblasting removed scratches near completely producing coarse and irregular surface of samples. Conclusions: Grinding, sandblasting and polishing could produce the transition of Zirconia Ceramic surface from t to m phase. It is better to use heat treatment after mechanical treatment to reverse the changed surface phase.

Abstract: To study whether the veneering technique will have an impact on zirconia grain and the bonding type and relationship on interface between zirconia and veneer porcelain. Materials and methods: After sintered, zirconia was annealed for 15 minute to finish the phase transition from m to t.4 types of veneer porcelains were sintered and observed with SEM (scanning electron microscopy) and TEM (transmission electron microscopy). Results: With etching time extending, it appeared that many materials loosed and corrosional pit deepened, enlarged in the veneer porcelain, which made crystallize structure move into veneering surface. Composition of interface mainly was amorphous glass matrix and zirconia. Energy spectrum analysis showed that there was no remnant glass composition in the zirconia side departing from interface. SEM showed that crystal in veneering side did not participate interface bonding. Conclusion: The interface between 4 types of veneer porcelains and zirconia bonded well. Veneering sintering technique didn’t change lattice structure of zirconia, which still was tetragonal structure. The specific bonding property of interface still remained to be analyzed further to determine.

Abstract: Objective: To study the effects of presintering temperature and temperature rise speed on the physical and mechanical properties of alumina-glass-composite (AGC). Methods: AGC was prepared respectively under the condition that presintered at 1400°C and 1450°C as well as two kind of temperature rise speed. The properties were measured, including density, thermal expansion coefficient, three-point bending strength, fracture toughness, modulus of elasticity and Vicker’s hardness of AGC. Results: With the increasing of presentering temperature and the temperature rise speed, density of AGC decreased, bending strength, fracture toughness, modulus of elasticity increased markedly. There was no difference between three-point bending strength and fracture toughness of AGC that was made by two temperature rise speed to 1450°C. Bending strength of AGC that was made by lower temperature rise speed to 1400°C was the lowest. The Vicker’s hardness of the 1450°C groups was higher than that of the 1400°C groups. Conclusion: Both presintering temperature and the temperature rise speed can influenced the properties of AGC, but the effect of presintering temperature was the most.

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: 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: 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.