Papers by Keyword: Dental Applications

Abstract: TiNi shape-memory properties are successfully used today for the fabrication of various technical devices. The limited machinability and high cost of TiNi encourage the use of near-net shape production techniques such as metal injection moulding. In this work TiNi alloys tensile test specimens are produced by metal injection moulding from pre-alloyed powders. A binder based on a mixture of polyethylene, paraffin wax and stearic acid is used. Parts with a density of about 96.6% of theoretical density are obtained. Scanning electron microscopy coupled with EDX measurements reveals a microstructure consisting of a TiNi matrix with small Ti₄Ni₂O_x and TiC inclusions. DSC and X-ray diffraction observations indicate the presence of additional Ni₄Ti₃ precipitates. The parts exhibit full superelasticity at room temperature even for strains of up to 4%, without the need for additional thermal post-treatments. Ultimate tensile strengths up to 980 MPa are obtained.

Abstract: Ceramics for dental applications have become increasingly important in the last decades. Particularly, the introduction of yttria-stabilized zirconia tetragonal polycrystalline (Y-TZP) materials as an alternative to the manufacturing of dental implants and prosthesis has provided a powerful tool to meet the demands required for these replacements in terms of biocompatibility, toughness, hardness and optical properties. Several commercial Y-TZP materials are currently available on the market and strong efforts in research and development facilities are being carried out to improve processing of Y-TZP to fully consolidate odontological pieces. Novel processing methods for ceramic powder sintering, including Y-TZP, aim to reduce processing times and production costs significantly, while maintaining or even improving the resulting microstructure and mechanical properties of the material. One of these methods includes microwave sintering. The purpose of this study is to characterize and compare the resulting properties of Y-TZP materials after conventional sintering and the non-conventional method of microwave heating. In this work one commercial material and one laboratory-synthesized Y-TZP powder are considered. The results suggest that microwave sintering results, generally, in better mechanical properties of the material in terms of hardness and fracture toughness than conventional sintering.

Abstract: The present paper put in evidence the mechanical behaviour of some commercial dental cobalt alloys, after own classification. The experimental cobalt alloys were classified in according either with molybdenum content, or with Cr+Mo content. A hierarcy of the alloys was finally made. The fractographic surfaces were investigate both by stereomacroscopy and scanning electron microscopy, putting in evidence the main structural features.

Abstract: Hydroxyapatite (HA) has been widely used as a biomaterial because HA has excellent biocompatibility, but the mechanical properties of HA are not sufficiently strong for dental applications. To enhance these mechanical properties, zirconia (ZrO₂) has been introduced as a second phase material. However, doping of ZrO₂ favors HA decomposition at low temperatures. In this paper, the effect of adding ZrO₂ on HA decomposition is discussed. Experimental results in previous studies are compared with theoretical results of chemical equations. The ideal percentage of doped ZrO₂ should be <10 wt.% to prevent HA decomposition unless a special sintering method is applied.

Abstract: The electrophoretic deposition (EPD) is a very promising process for shaping compacts, especially for nanopowders. Up till now EPD is not used on a large-scale production of ceramic products. Additionally, the higher cost of nanopowders was also a barrier for the development of new products. As the deposition rate at EPD is independent of particle size, it is an ideal process for shaping compacts of powder mixtures with nanopowders. Silica and zirconia powders were used as model systems to demonstrate the advantages of EPD. Applications might be the preparation of high-purity silica glass for processing of semiconductors and zirconia ceramics for near net-shaped dental crowns. In both cases the optimum green density was achieved for approx. 10 % addition of nanopowders to a coarser matrix powder. The compacts were homogenous. Alternatively, compacts of different powders can be prepared in a two-step process. Examples are shown for the electrophoretic impregnation (EPI) and a reactive forming of nanoparticles inside the pore volume of a compact consisting of coarser particles.

Abstract: In the last decades many investigations have been oriented toward the development of nanostructured biomaterials such as calcium phosphate ceramics, particularly those composed of stoicheiometric hydroxyapatite (Ca10(PO4)6(OH)2) and a-and β- tricalcium phosphate (Ca3(PO4)2), which present chemical and crystallographic similarities with hard tissues (bones and teeth). Because of these characteristics, these materials can be used for reconstitution and regeneration of bone tissues. The odontological and biomedical applications are still limited due to their brittle behaviour. This study was focused in the synthesis and characterization of a bone matrix of calcium phosphate (β-TCP) and hydroxyapatite (HAP-101 e HAp-201). The results presented here are related to the morphological characterization of nanostructured powders from scanning electron microscopy viewpoint. X-ray diffraction was used to identifier the present phases in the powders and the infrared spectrometry (FTIR) was used to analyse OH bonds from hydroxyapatite and PO4 from calcium phosphates.

Abstract: This study was conducted to evaluate the influence of surface roughness on anchoring strength between ceramic and coating glass. Commercial Vita alpha glass-ceramic was selected as the coating glass, while the zirconia/alumina (Z/A) composite as the substrate. Anchoring strength between substrate and coating-glass was tested, and microstructure of the junction was also observed. From the experiments we can find the following results. There was significant difference in the mean strength of different surface roughness groups and HF acid-etching also had a favorable effect on matching properties. The highest amount of anchoring strength was occurred at the high scope of roughness after HF acid-etching and surface roughness will also affect the microstructure of the junction. Therefore, we can draw the conclusions that with the limit of this research, roughness will influence matching properties between ceramic substrate and coating-glass, while hydrofluoric acid etching was also suggested in the matching procedure. Testing matching properties between ceramic substrate and coating-glass should consider the influence of surface roughness.

Abstract: The aim of this study was to analyze the microstructure and to observe the surface reactivity of a composite system composed of two kinds of zirconia/alumina (Z/A) composites and Vita alpha glass-ceramic, which would satisfy the biocompatibility and strength requirements for dental applications. Two zirconia/alumina composites defined as specimen A and B were used as the substrate of fixed partial denture, while commercial Vita alpha glass-ceramic as the coating-glass.
From the experiment we can find the following results. Zirconia particles migrated into grain boundaries and located at three or four grain junctions of alumina particles. The crack pattern is consistently transgranular for the zirconia grains, whereas it is intergranular for alumina grains. The mechanical properties of the composite with 66.6wt% zirconia was superior to that of 33.3wt% zirconia-composed composite, while the homogeneous bond between Vita alpha glass-ceramic and Z/A composites are distinct. Therefore, this system composed of Z/A composites and Vita alpha glass-ceramic would satisfy matching properties of dental requirements and it has a great future to be used as all-ceramic restoration materials.