Papers by Author: Jie Mo Tian

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: 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: Bilayered three-point bending strength specimen of KAVO zirconia-Vita VM9 veneering porcelain were made according to ISO6872 standard, the core to porcelain thickness ratio was 1:1. Specimens were subjected to multiple dentine porcelain firing cycles. Three-point bending strength were tested, SEM was used to observe the characteristics of the failure mode. Results show that there was no influence on the bending strength by multiple firing, the three-point bending strength were 996 ~ 1020 MPa after multiple firing, and no obvious defects was found at the interfaces. In all bilayered specimen, the bulk fracture initiated at the tensile surface of the core material and was consistently accompanied with porcelain crush and delamination at the interface.

Abstract: Objective: to investigate glass infiltrating rates (depth/time) within dental CAD/CAM alumina at different temperatures. Methods: micron α-alumina powder was prepared with cold isostastic pressure at 250 MPa and sintered at 1450°C. The presintered alumina specimens were then infiltrated with special glass at 1150°C, 1200°C and 1250 °C. The infiltrating depths and time to form the infiltrate at the different temperatures were evaluated. Results: As the infiltrating temperature increased, the viscosity of the infiltrating glass decreased, and the infiltrating depth increased. A 1 mm infiltration depth into the presintered alumina at 1150°C, 1200°C and 1250°C required 95 min, 22 min and 8 min, respectively. Conclusion: An optimal infiltrating time required to reach a suitable infiltration depth into the presintered alumina was observed at 1200°C, an important finding for clinical applications at this commonly used furnace temperature.

Abstract: Objective: To study the relative translucency of 3 veneered and glazed all-ceramic systems core material, including Vita In-Ceram Alumina, Vita In-Ceram Zirconium and Ivoclar Vivodent Empress. Methods: Under standard black and write background, the surface light reflectivity of 3 veneered all-ceramic systems core material was determined with contact color difference meter, and the ratio of Yb /Yw was calculated. Results: After veneered, the relative translucency of 3 core materials all declined, and ranged from 0.8880 of Empress II to 1.00 of In-Ceram zirconia, among of that Empress II was most transparent. Conclusion: The relative translucency of 3 veneered all-ceramic systems core material had significant statistical difference. There was a decreasing range as Vitadur Alpha dentin (standard) > Empress II (0.8 mm) > In-Ceram Alumina > In-Ceram Zirconia.

Abstract: Objective: To study the relative translucency of 3 all-ceramics system core material, including Vita In-Ceram Alumina, Vita In-Ceram Zirconium and Ivoclar Vivodent Empress II. Methods: The visible light transmittance of all samples was determined with spectrophotometer. Results: The relative translucency of dentin and opaque dentin was between 0.5958 and 0.8336, that of 3 core ceramic ranged from 0.8089 of Emp ress II to 1.00 of In-Ceram Zirconium. Conclusion: The relative translucency of 3 core material was significantly different. There was a decreasing range as Empress II > In-Ceram Alumina and In-Ceram Zirconia.

Abstract: To study the influence of background color on 3 veneered all-ceramic core materials, the color of all veneered samples that were put on noble metal, Ni-Cr alloy, Ag-Hg alloy and resin background was measured with chromatism instrument (and the chromatic aberration value among groups was Calculated). Under different backgrounds, there was significant difference in the L, a and b values among Empress II samples, there was significant difference in a and b values among In-Ceram Alumina samples, and there was no difference in the L, a and b values among In-Ceram Zirconium samples. After veneered, the influence of background color on Empress II was clear, on In-Ceram Alumina was less clear, and on In-Ceram Zirconium was void.