Papers by Keyword: Dental Ceramic

Abstract: Dental prostheses made of ceramic composites infiltrated with glasses have been used due to their biocompatibility and possibility to mimic the natural teeth. In this study, the devitrification behavior of 20SiO₂-25B₂O₃-25Al₂O₃-15La₂O₃-15TiO₂ glass during the infiltration process in a porous alumina preform was investigated. Glass frits were prepared by melting the raw materials at 1500 °C for 60 min. The glass was infiltrated into the alumina preform at 1,150 or 1,200 °C for 60 min. The specimens were characterized by X-ray diffraction analysis and scanning electron microscopy. After the infiltration, it was possible to note that the devitrification process occurred in the remaining glass (excess glass that did not infiltrate in the preform), forming mostly aluminum borate and mullite crystalline phases. However, within the infiltrated composite no devitrification was noticed in the infiltrated glass. Possible explanations for this behavior are discussed.

Abstract: Dental ceramics has become dominant materials used in dental restorations. Dental ceramics have several advantages, such as stable performance, good bio-compatibility, little possibility to attach plaque, and similarity to the color of permanent tooth. However complex surface characteristics and hard and brittle properties of dental ceramic materials caused difficulties in the processing and subsequent grinding. The complicated craft and high failure rate of dental ceramics greatly limit its wide application in clinical. Thus, fully understanding the special cutting tools grinding performance and researching the material damage process caused by grinding temperature and grinding force are of great significance. Research on dental ceramic grinding was reviewed in this paper. The removal mechanism of dental ceramic materials and the influence of parameters settings on the grinding force, grinding temperature, and the surface quality have been studied. Besides the existing problems in dental ceramic grinding technology were pointed out.

Abstract: The purpose of this study was to study the surface characteristics of the dental 3Y-TZP (3 mol% yttria stabilized tetragonal zirconia) ceramic treated by machining process and analysis what impact on the mechanical properties of the 3Y-TZP dental restorations. Dense core ceramic discs were made of 3Y-TZP. The samples were partially sintered to get part strength after uniaxial pressure moulding. The partially sintering green body could be treated by grinding, incising and milling and incising to simulate the CAD-CAM (computer aided design/computer aidedmanufacturing) process in dentistry. The partially sintering samples were then sintered to achieve full density. The dense sintered ceramics were also treated by grinding and incising to simulate the dental restorations adjusting process in dental clinic. The both surface of thespecimens were studied with an optical microscope and field emission SEM. Bulges were observed on the surface of the sample after uniaxial pressure moulding process. The defects due to partially sintered green body milling process were different from incising process in size and shape. Groves are observed on the surfaces of the samples after grinding process. The conclusions were that (i) machining of the final sintered dental 3Y-TZP ceramic brought more critical damage than the machining of partly-sintered green-bodies; (ii) the milling process ofthe partially sintered green-body brought less damage to the 3Y-TZP samples than the incising process.

Abstract: The use of zirconia dental ceramics has grown in recent years due to improvements in esthetics and biocompatibility. Zirconia is used in dental applications for its high strength and fracture toughness. In this research, the influence of sintering conditions on the strength and optical properties of zirconia was investigated. Spray dried granules of 3Y-TZP zirconia were die pressed into disc-shaped samples and cold isostatic pressed at 250 MPa. Sintering was conducted using either one step sintering at 1500 oC or two-step sintering, with pre-sintering at 1200 oC and final sintering at 1500 oC. Heating rates of 2 and 10 oC/min were used. The biaxial flexural strength, fracture toughness, density, microstructural characteristics and optical properties of the sintered samples were determined. It was found that the sintering conditions did appear to influence the mechanical and optical properties. The sintering conditions had no significant effect on the density. It was concluded that for the sintering conditions examined, the two-step sintering with a heating rate of 2 oC/min produced the best average mechanical and optical properties of 3Y-TZP zirconia.

Abstract: The use of zirconia crown has attracted considerable attention due to its good mechanical and optimal biocompatility. The white color of zirconia does not allow for perfect aesthetic characteristics though. Colorized zirconia blocks with Pr₆O₁₁, Er₂O₃ and Fe₂O₃ gradient concentration and the shade stability were investigated. Chromatic values of the samples were presented in CIELab system, and the shade stability was evaluated by color comparison of samples in the same group. The value of L* from 68.2-84.0, a* from-1.8-5.9, and b* from 18.6-33.2 can be obtained. These values can be comparable to the Vita 3D master system. The E between the samples of every group was below 2.2. The results showed that by adding combined oxides of gradient concentration could reproduce the tooth-like color of zirconia ceramics, and the shade stability was satisfied.

Abstract: It is significant to explore the fatigue contact damage of bi-layer ceramic composites in order to improve the long-time mechanical reliability of bi-layer structured dental restorations. In this study, Hertz contact test was used to compare the fracture modes and the ability of anti-fatigue damage of zirconia and alumina bi-layer composites, to analyze the effect of loading rate and other factors on the damage mechanisms of bi-layer ceramic composites. Cyclic spherical fatigue loading was put on the bi-layer alumina and zirconia composites with different substrates. The samples were observed by high depth of field stereomicroscope and digital optical microscope after test. The results showed that the fatigue contact damage mode of zirconia bi-layer composite was the porcelain fracture from radial cracks without the damage of zirconia core. The fatigue contact damage mode of alumina bi-layer composite was the alumina core failure from radial cracks as the function of contact load. For both of zirconia and alumina bi-layer samples, the number of cycles to the sample failure as the function of same maximum contact load with high loading rate was obviously smaller than low loading rate. The mechanical properties of the substrate materials had limited effects on the number of cycles to the failure of both zirconia and alumina bi-layer samples from contact-induced radial cracks as maximum contact load with low loading rate. The ability of the zirconia bi-layer composites to resist fatigue damage was much higher than that of the alumina bi-layer composites.

Abstract: Objective:To study the relative translucency of 5 veneered and glazed all-ceramic systems core material, including Procerra AllCeram Alumina, Vita In-Ceram Zirconium, Ivoclar Vivodent Empress, In-Ceram Spinell and Colored Zirconia. Methods: Under standard black and white background, the surface light reflectivity of 5 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 5 core materials all declined, and ranged from 0.6740 of In-Ceram Spinell to 1.00 of In-Ceram zirconia, among of that In-Ceram Spinell was most transparent. Conclusion: Among the groups, there is no significant differences among Empress II, Procera AllCeram and Colored Zirconia (IL1,IL2,IL3). Compared with Procera AllCeram and Vita In-Ceram Zirconium , Procera AllCeram has significant difference. There is a significant difference between Procera AllCeram and In-Ceram Spinell.

Abstract: This study aims to investigate the difference on relative translucency of four systems of dental all-ceramic zirconia materials which are all at clinical required thickness.All-ceramic zirconia specimens containing Zenostar,Lava,Cercon and Upcera are fabricated into discs with 10mm in diameter and 0.5±0.01mm in thickness.The relative translucency of specimens are measured with color difference meter,and the measurements are conducted statistical analysis with software SPSS13.Experimental results display that their relative translucency are significantly different,which decrease in sequence of Zenostar,Lava,Cercon and Upcera zirconia.Cercon zirconia with certain translucency could be used for relatively opaque posterior tooth.As for discolored teeth,Upcera Zirconia may be advisable.

Abstract: This study aims to investigate the difference on transmittance of four systems of dental all-ceramic zirconia materials which are at clinical required thickness,IPS e.max Press used as control.All-ceramic zirconia specimens containing Zenostar,Lava,Cercon and Upcera,are fabricated into discs with 10mm in diameter and 0.5±0.01mm in thickness.The transmittance of disc specimens are measured by using PR2650 spectrophotometer and the measurements are conducted statistical analysis with software SPSS13.Experimental results reveal that the transmittances of four systems of zirconia materials are significantly different.Their transmittances decrease in sequence of IPS e.max Press ,Zenostar,Lava,Cercon and Upcera zirconia.Zenostar and Lava Zirconia,which have good optical effects,possess ideal restorative materials for anterior teeth with higher transmittance.

Abstract: Objective: To study the relative translucency of 4 veneered and glazed all-ceramic systems core material, including Vita In-Ceram Alumina, Vita In-Ceram Zirconium, Ivoclar Vivodent Empress and Colored Zirconia. Methods: Under standard black and write background, the surface light reflectivity of 4 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 4 core materials all declined, and ranged from 0.8015 of Colored Zirconia to 1.00 of In-Ceram zirconia, among of that Empress II and Colored Zirconia were most transparent. Conclusion: Among the groups, there is no significant difference between Empress II and Colored Zirconia(IL1,IL2,IL3). Compared with Vita In-Ceram Alumina and Vita In-Ceram Zirconium, Vita In-Ceram Alumina(AL1) has significant difference. There is no significant difference between Vita In-Ceram Zirconium and Vita In-Ceram Alumina(AL2,AL3,AL4).