Papers by Keyword: Dental Material

Abstract: It has been tried to develop Ti-Ca alloys which demonstrates corrosion resistance in an aqueous fluoride solutions. The Ti-Ca alloys were produced by diffusion-metallizing method. A Ti plate and Ca grains were put in a sealed container of stainless steel. As the container was heated at 1000 oC, Ca was melted and partially vaporized in the inner space. Ca then contacts and permeats into the Ti plate to metallize. In a holding time of 450 h, the alloy surface consisted of two layers, the first was oxide layer and the second was metal layer of about 200 m thick. A Vickers micro hardness of the second layer was quite large, upto about 600 Hv. Evaluation of corrosion resistance for the second layer and the inner part was carried out by electrochemical potentiokinetic method. Test solutions were aqueous fluoride solutions produced with HF and NaF. A concentration of fluoride ion was fixed to 0.024 kmol m-3, and pH of the solution was varied from 3.4 to 4.7. As a result, both Ti and Ti-Ca alloy were passivated under natural immersion condition in the solution of pH 4.7. At pH 3.4, on the other hand, Ti was actively dissolved, but Ti-Ca alloy was still passivated, that means Ti-Ca alloy performs much better corrosion resistance than Ti.

Abstract: The aim of this work was to establish a route to produce pre-sintered blocks of Y-TZP (yttria stabilized tetragonal zirconia polycrystal) suitable to be machined in a commercial CADCAM system, used to manufacture crowns and bridge frameworks for dental applications. Two commercial Y-TZP powders were investigated. The powders were pressed with different compaction pressures (40 to 500 MPa) and pre-sintered at temperature ranging from 900 to 1100°C. Vickers hardness, biaxial flexural strength, and linear shrinkage could be correlated to the relative density of pre-sintered samples. Using an empirical equation, pre-sintered blocks with a pre-defined density could be prepared. The blocks withstood the machining in a CAD-CAM system, and the machined and sintered crowns presented good adaptation.

Abstract: The aim of this work was to study the effect of temperature and heating rate on the densification of two leucite-based dental porcelains: one low-fusion and one high-fusion commercial leucite porcelains (Dentsply-Ceramco). Porcelain powders were characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), particle size distribution, and helium picnometry. Bar samples were sintered from 650 to 1050oC, using heating rate of 55oC and 10oC/min. Sintered samples were characterized in terms of bulk density, measured by the Archimedes method in water, and fractured surface microstructure by scanning electron microscopy (SEM). The results show that densification increases with increasing temperature and the increase in heating rate has no effect on the densification of the porcelains studied.

Abstract: Leucite (KAlSi2O6) is the main crystalline phase in feldspathic dental materials used for ceramic-fused-to-metal restorations. It occurs in two modifications, low temperature – tetragonal and at temperatures above 600 °C high temperature – cubic modification. The aim of this work was to develop a low-temperature preparation technology of submicron leucite powders with varying ratio of tetragonal and cubic modification. The results show that analcime synthesized in hydrothermal conditions is the suitable precursor for the preparation of leucite with controlled fraction of the c-modification. Homogenous t-leucite having particle size from 2 - 4 μm was prepared by 4h ion-exchange in 4M KCl. Partially stabilized c-leucite was obtained by dual ionexchange; 4h in 4M CsCl led to 48 % of c-modification in the final product.

Abstract: The use of specific remineralizing agents in toothpastes may help to prevent caries and treat dentinal sensitivity. In this study, applied nanotechnologies were used to develop a filler for toothpastes with remineralizing properties. Carbonate hydroxyapatite nanocrystals, with size, morphology, chemical composition and crystallinity comparable with that of dentine, were synthesized in mild condition. The remineralizing effect was studied with a scanning electron microscopy putting materials onto the slices of dentine previously demineralized with ortophosphoric acid. The application of the materials showed the progressive closure of the tubular openings of the dentine with plugs within 10 minutes and a regeneration of a surface mineral layer within 6 hours. This rates of remineralization seems to be compatible with the development of toothpastes with remineralizing effect.

Abstract: Non-toxic allergy free alloying elements are mostly selected for preparing metallic biomaterials. Currently, functionalities such as low modulus, shape memory, super elasticity, etc. are required for the metallic biomaterials, especially for β type titanium alloys. The harmonization of metallic, ceramic, and polymer biomaterials is needed for advanced biomaterials in the future. Titanium and its alloys are attracting considerable attention with regard to applications not only in the biomedical field, but also for dental and healthcare products. In dentistry, titanium and its alloys are applied to dental products such as crowns, inlays, bridges, etc., as well as dental implants. For fabricating dental products, the dental precision casting process is important. A new dental precision casting process using calcia is currently being developed. Noble alloys such as gold base or silver base alloys are widely applied for the precision casting of dental products. Allergy-free elements, particularly Pd-free low- noble dental alloys are required.

Abstract: Metal-ceramic systems play very important role in the prosthetic dentistry. The most widely used metallic alloys are the Ni-Cr, Co-Cr, Au-based alloys and Ti. The bonding strength between the metal base and the ceramic covering layer can be very different in different systems and is strongly affected by the firing conditions as well. For the further improvement of the bonding properties the detailed knowledge of the microstructure of the metal–ceramic interlayer is essential. In this work our results, obtained by scanning and transmission electron microscopy on systems of commercial alloys and corresponding porcelains will be reviewed.