Papers by Keyword: Dental Ceramic

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: Bi-layer all-ceramic dental crowns comprise an inner core made of alumina or zirconia and an outer porcelain shell. The veneer safe from damage is mainly depended on the properties of core materials due to the poor strength and toughness of porcelain. The fracture modes and crack transformation of zirconia/porcelain and alumina/porcelain bi-layer composites reveal the potential feasibilities of improving the fatigue life of all-ceramic restorations. The failure modes of bi-layer composites were confirmed under cyclic spherical fatigue loading by dynamic microcosmic observation. Crack modes and evolvement of bi-layered composites were explored inflecting with fatigue load, cycles, frequency and water environment. Microcosmic morphology of the samples was observed by high depth of field stereomicroscope to determine degree and modes of fatigue damage. The appearance of cone cracks of porcelain surface was almost consistent in both of zirconia and alumina bi-layer composites. However, the pattern and process of the damage are different under cycle fatigue load. Furthermore, process of fatigue damage of bi-layer composites were observed to failure rapidly under water environment in both of zirconia and alumina bi-layer composites.

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: This study was focused on the testing and assessment of the mechanical properties of nanometric zirconia dental ceramics. The density and the apparent porosity of specimens were tested with the Archimedes drainage method. The length variation of the specimens before and after sintering was measured with a vernier caliper, and the linear contraction was tested. An X-ray diffractometer was used for the specimen phase analysis. SEM was used to observe the section micrograph of the specimens. A universal mechanical testing machine was used to test the three-point flexural strength and the fracture toughness. A microhardness tester was used to test the Vickers hardness of the test specimens. Results indicates that the flexural strength of the test specimens ≥ 890MPa, the fracture toughness ≥6Mpa.m^1/2, the Vickers hardness ≥ 1240MPa, the linear contraction ≥ 21%, and the apparent porosity ≥ 0.32%. Fully satisfying the requirements in oral medicine, the ceramic is an ideal material for biological joints and dental prosthesis.

Abstract: This study was focused on the theoretical analysis and experimental investigations about the frictional wear of nanometric zirconia dental ceramics. An MRH-3 digital-display high-speed ring-on-block tribometer was used for frictional wear experiments. A PGI800 coarseness profiling instrument was used to test the width and the length of the grinding defects on specimen surfaces. An S-3500N SEM was employed in the microscopic observation of the surface morphology after the abrasion. Results indicated that the frictional factor and the wear rate of nanometric ZrO₂ ceramics decreased significantly under identical working and frictional conditions compared with ZrO₂. The wear mechanism of nanometric ZrO₂ ceramics was micromachining and plastic deformation while the wearing mechanism of ZrO₂ ceramics was brittle fracture and abrasive wear.

Abstract: The purpose of this study was to evaluate the crystal phase formation behavior and its influence on the mechanical properties of LiO2-SiO2-P2O5 glass-ceramics system. High temperature XRD was used to analyze the crystal phase formation in situ. The crystalline phases in the material both before and after heat-treatment were also analyzed. The flexural strength was measured by three-point bending test according to ISO 6872:2008(E). The SEM analysis showed that the high strength of the glass-ceramics is attributed to the continuous interlocking microstructure with fine lithium disilicate crystallines.

Abstract: This paper focused on the properties of Al2O3-rainforced feldspar dental ceramic. The results indicated that the introduced Al2O3 could elevate the density of the sintered feldspar ceramic, where the relative density reached 97.9% under the conditions of 20 wt% Al2O3 additive and 1200°C. On the other hand, Al2O3 additive could remarkably promote the machinability and the ultimate bending strength of the modified feldspar ceramic. The grinding efficiency increased by 260.1% if the content of Al2O3 additive was 5 wt%, while the ultimate bending strength enhanced under increasing Al2O3 additive content. The microstructure analysis revealed a composition of α-Al2O3 as the dominant phase and crystalline calcium aluminum silicate hydrate as the minor phase in the Al2O3-rainforced feldspar ceramic. The feldspar represented totally as glass phase, wherein the Al2O3 grains showed a homogenized dispersion.

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.