Papers by Author: Qi Liu

Abstract: Firstly, the conservation issue in the Xiaoling Mausoleum Sacred-way area is discussed, and the form and development of the historic landscape is revealed. Secondly, the protection goals and principles are put forward by the analysis of historical landscape concepts. Finally, an appropriate ways and methods for complicated historical landscape is demonstrated with the planning practice in this area.

Abstract: Dentine porcelain disc specimens 13.0 mm in diameter with thicknesses of 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, and 6.0 mm, were made using IPS E.max color systems B, C, and D and their chromatic aberration values (ΔE) under the standard black background and the standard white background were measured using a Minolta CM-5 spectrophotometer. Then, the cubic regression formula of best fit was used to calculate the thicknesses of dentine porcelains of various color numbers at a ΔE of 1.0 and 1.5. The determination coefficient of the regression formula of color system B was 0.990–0.995, that of color system C was 0.989–0.997, and that of D was 0.993–0.998; and R² is close to 1. The results show that the regression formulas of the 11 thickness groups have good fit. The infinite optical thickness values of the IPS E.max dentine porcelains were as follows: for B1–B4, 3.263–2.711 (ΔE = 1.0) and 2.910–2.493 (ΔE = 1.5); for color system C, 2.727–2.611 (ΔE = 1.0) and 2.473–3.365 (ΔE = 1.5); and for color system D: 2.928–3.694 (ΔE = 1.0) and 2.656–2.458 (ΔE = 1.5). When the chromatic aberration tolerance is 1.5, the thickness of dentine porcelain required to reach the infinite optical thickness is less than the numerical value at ΔE = 1.0. As the thickness increases, the influence of the background diminishes and the specimen looks truer to its inherent color. The results prove that thickness of dentine porcelain positively correlates with its masking ability and that its thickness must exceed its infinite optical thickness so that its color will not be influenced by the background color.

Abstract: In this study, the binding performance of a Cercon-based zirconia framework material and special Cercon Ceram S zirconia veneering porcelain is discussed. Rectangular 30 mm × 20 mm × 2 mm porcelain blocks were made from zirconia using the CAD/CAM system. The 2 mm veneering porcelain was then sintered onto blocks at a temperature of 850-800°C with a loading speed of l mm/min. The shear bond strength of the interface was tested. Sintering was studied by visual observation, scanning electron microscopy, energy dispersive spectroscopy (EDS), thermal shock test and other methods. Excellent sintering results of the zirconia framework material and veneering porcelain can be achieved. The cross-sectional morphology of the samples, observed by SEM, shows a uniform, fine, and smooth texture for the veneering porcelain, whereas that of the zirconia framework material shows a rough surface with a uniform and compact texture. EDS results indicate that a small amount of A12O3 and SiO2 is present in the zirconia area, and no ZrO2 or Y2O3 is detected in the veneering porcelain area. No interlayer radial crack or flaw is found throughout the entire thermal shock test of the samples at 60-240°C. Thus, the cracking temperature of the samples is pegged at T>240°C. The shear bond strength of the interface is 32.62±5.77 MPa. Chemical element infiltration exists between zirconia and the veneering porcelain, indicating the chemical bond between the two. An excellent match between the Cercon-based zirconia framework and the special veneering porcelain can be achieved, which can satisfy clinical requirements.

Abstract: This study aims to investigate the effect of background color on the chromatic value of four all-ceramic system core materials at clinically appropriate thicknesses. Disc specimens with 15 mm in diameter and thicknesses ranging from 0.5±0.01mm In-Ceram zirconia core, Cercon base zirconia core, and Cercon base color zirconia core) to 0.8±0.01mm (Empress II) were fabricated. A colorimeter (CIE- 1976-Lab) measured the chromatic value of all samples placed on a high-noble metal-ceramic alloy and a visible light-cured dental composite resin (A2 color) background, after which the color difference was calculated. The color difference of Empress II samples was more than 1.5 among different background color groups, while that of Zirconia was less than 1.5. The influence of background color on the Empress II dentin was visible, such that it could be used on a tooth color post. Meanwhile, the influence of background color was invisible for the three kinds of Zirconia core materia1s, such that the materials developed excellent color-masking abilities and could be adapted for use on any color background.

Abstract: The surface microhardness and flexural strength of colored zirconia were examined. Two groups of zirconia disks (1mm thick, 20mm in diameter) within 5 disks each were shading with the same coloring liquids IL2 (Vita Classic-scale) when another group of 5 disks measured in no color. The shading time of one group was 3s and that of the other group was prolonged to 30s. The mechanical properties were tested after sintering at 1500°C. Data were evaluated using ANOVA analysis. Disks of shading 30s showed a lower strength 712  53 MPa. The value of 3s was 853  46 MPa. There were no significant difference on microhardness between the two shading time. Prolonged the shading time lowered the biaxial flexural strength of zirconia ceramic, but shading time did no effect on surface microhardness.