The Experts below are selected from a list of 150 Experts worldwide ranked by ideXlab platform

F S Silva - One of the best experts on this subject based on the ideXlab platform.

  • experimental evaluation of the bond strength between a cocrmo Dental Alloy and porcelain through a composite metal ceramic graded transition interlayer
    Journal of The Mechanical Behavior of Biomedical Materials, 2012
    Co-Authors: Bruno Henriques, Michael Gasik, Delfim Soares, F S Silva
    Abstract:

    Abstract Objectives The purpose of this study was to evaluate the shear bond strength between CoCrMo Dental Alloy and porcelain restorations by application of different metal–ceramic transitional interfaces aiming at improvement of the bond strength and fracture tolerances. Methods Several metal–ceramic specimens with different composite interlayers were produced. The interlayers consisted of metal/ceramic composites with different metal volume fractions (20 M; 40 M; 60 M; 80 M). The metal–ceramic bond strength as well as the fracture strength of the composites and monolithic base materials were assessed by the means of a shear test performed in a universal test machine. The interfaces of fractured and untested specimens were examined by the means of optical microscopy. The microstructures of monolithic base materials were analyzed using SEM/EDS. The elastic and inelastic properties of the homogeneous compositions were additionally evaluated using dynamic mechanical analysis. Results The bond strength results obtained for metal–ceramic gradated specimens were the highest (261±38 MPa) for 40 vol% metal in the interlayer [40 M] vs. 109±27 MPa for a direct metal–ceramic joint. The Young's moduli and the fracture resistance of the composites revealed an increasing trend for increasing metal contents. Significance This study shows that a graded transition between metal and ceramic, provided by a metal/ceramic composite interlayer, is regarded for an increase by 2.5 times in the bond strength between the two materials relative to conventional sharp transitions. The elastic modulus of the composites used as interlayers might be very reasonably approximated by a micromechanical model.

  • microstructure hardness corrosion resistance and porcelain shear bond strength comparison between cast and hot pressed cocrmo Alloy for metal ceramic Dental restorations
    Journal of The Mechanical Behavior of Biomedical Materials, 2012
    Co-Authors: Bruno Henriques, Delfim Soares, F S Silva
    Abstract:

    Abstract Objectives: The purpose of this study was to compare the microstructure, hardness, corrosion resistance and metal–porcelain bond strength of a CoCrMo Dental Alloy obtained by two routes, cast and hot pressing. Methods: CoCrMo Alloy substrates were obtained by casting and hot pressing. Substrates’ microstructure was examined by the means of Optical Microscopy (OM) and by Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). Hardness tests were performed in a microhardness indenter. The electrochemical behavior of substrates was investigated through potentiodynamic tests in a saline solution (8g NaCl/L). Substrates were bonded to Dental porcelain and metal–porcelain bond strength was assessed by the means of a shear test performed in a universal test machine (crosshead speed: 0.5 mm/min) until fracture. Fractured surfaces as well as undestroyed interface specimens were examined with Stereomicroscopy and SEM-EDS. Data was analyzed with Shapiro-Wilk test to test the assumption of normality. The t-test ( p 0.05 ) was used to compare shear bond strength results. Results: Cast specimens exhibited dendritic microstructures whereas hot pressed specimens exhibited a typical globular microstructure with a second phase spread through the matrix. The hardness registered for hot pressed substrates was greater than that of cast specimens, 438±24HV/1 and 324±8HV/1, respectively. Hot pressed substrates showed better corrosion properties than cast ones, i.e. higher OCP; higher corrosion potential (E corr ) and lower current densities (i corr ). No significant difference was found ( p 0.05 ) in metal–ceramic bond strength between cast (116.5±6.9 MPa) and hot pressed (114.2±11.9 MPa) substrates. The failure type analysis revealed an adhesive failure for all specimens. Significance: Hot pressed products arise as an alternative to cast products in Dental prosthetics, as they impart enhanced mechanical and electrochemical properties to prostheses without compromising the metal–ceramic bond strength.

Spiros Zinelis - One of the best experts on this subject based on the ideXlab platform.

  • selective laser melting technique of co cr Dental Alloys a review of structure and properties and comparative analysis with other available techniques
    Journal of Prosthodontics, 2015
    Co-Authors: Theodoros Koutsoukis, Khalid Alwazzan, Mohammed Qasim Al Rifaiy, Spiros Zinelis, George Eliades, Y Al S Jabbari
    Abstract:

    Purpose The aim of this study was to review the effect of selective laser melting (SLM) procedure on the properties of Dental structures made of Co-Cr Alloys and to evaluate its quality and compare it to those produced by conventional casting and milling fabrication techniques. Materials and Methods A computerized database search using PubMed and Scopus was conducted for peer-reviewed scientific research studies regarding the use of SLM in Co-Cr Dental Alloys with no restrictions for publication years. The search engines provided hundreds of results, and only 48 scientific research papers, case studies, or literature reviews were considered relevant for this review. Results The innovative manufacturing concept of SLM offers many advantages compared with casting and milling fabrication techniques. SLM provides different microstructure from casting and milling with minimal internal porosity and internal fitting, marginal adaptation, and comparable bond strength to porcelain. Mechanical and electrochemical properties of SLM structures are enhanced compared to cast, while clinical longevity of single-metal ceramic crowns is comparable to Au-Pt Dental Alloy. Conclusion The SLM technique provides Dental prosthetic restorations more quickly and less expensively without compromising their quality compared with restorations prepared by casting and milling techniques. Clinical significance: The current SLM devices provide metallic restorations made of Co-Cr Alloys for removable and fixed partial dentures without compromising the Alloy or restoration properties at a fraction of the time and cost, showing great potential to replace the aforementioned fabrication techniques in the long term; however, further clinical studies are essential to increase the acceptance of this technology by the worldwide Dental community.

  • surface and elemental alterations of Dental Alloys induced by electro discharge machining edm
    Dental Materials, 2007
    Co-Authors: Spiros Zinelis
    Abstract:

    Abstract Objectives To evaluate the surface and elemental alterations induced by electro discharge machining (EDM) on the surface of Dental cast Alloys used for the fabrication of implant retained meso- and super-structures. Methods A completed cast model of an arch that received Dental implants was used for the preparation of six wax patterns which were divided into three groups (Au, Co and Ti). The wax patterns of the Au and Co groups were invested with conventional phosphate-bonded silica-based investment material and the Ti group with magnesia-based investment material. The investment rings of the Au and Co groups were cast with an Au–Ag Alloy (Stabilor G) and a Co–Cr base Alloy (Okta C), respectively, while the investment rings of group Ti were cast with cp Ti (Biotan). One casting of each group was subjected to electro discharge machining (EDM); the other was conventionally ground and polished. The surface morphology and the elemental compositions of conventionally and EDM-finished surfaces were studied by SEM/X-ray EDS analysis. Six spectra were collected from each surface employing the area scan mode and the mean value of each element between conventionally and EDM-finished surfaces was statistically analyzed by t -test ( a  = 0.05). Then the specimens of each group were cut perpendicular to their longitudinal axis and after metallographic grinding and polishing the cross-sections studied under the SEM. Results The EDM surfaces showed a significant increase in C due to the decomposition of the dielectric fluid during spark erosion. Moreover, a significant Cu uptake was noted on these surfaces from the decomposition of the Cu electrodes used for EDM. Cross-sectional analysis showed that all Alloys developed a superficial zone (recast layer) varying from 2 μm for Au–Ag to 10 μm for Co–Cr Alloy. Significance The elemental composition of Dental Alloy surfaces is significantly altered after EDM treatment.

J N Wang - One of the best experts on this subject based on the ideXlab platform.

  • strengthening of a pd free high gold Dental Alloy for porcelain bonding by a pre firing heat treatment
    Dental Materials, 2007
    Co-Authors: J N Wang
    Abstract:

    Abstract Objectives The purpose of the present investigation was to report a Pd-free high gold Alloy for porcelain bonding based on the ternary system of Au–Pt–Zn with a nominal composition of 86Au–11Pt–1.5Zn–0.5In–0.7Rh–0.2Fe–0.1Ir (wt.%). Emphasis was put on the effect of a pre-firing heat treatment on the mechanical properties of the Alloy. Methods The strengthening effect of the pre-firing heat treatment was investigated by means of hardness measurement, tensile testing, X-ray diffraction, optical microscopy and scanning electron microscopy. Results Experimental results showed that both the hardness and tensile strength of the Alloy can be significantly improved after heat treatment at the temperature of 980 °C for 15 min. The strengthening could be attributed to homogenization of microstructure and Alloying elements and precipitation of new fine particles. Significance The cast framework of the present new Pd-free Alloy could be heat treated before actual firing, and this would improve the processing properties of the Alloy during firing.

  • a pd free high gold Dental Alloy for porcelain bonding
    Gold Bulletin, 2006
    Co-Authors: J N Wang
    Abstract:

    Recently, some side effects of Pd, such as allergies, were found, and the risk of using Pd in Dental casting Alloys was raised. The purpose of the present investigation is to report a Pd-free high gold Alloy for porcelain bonding. Emphasis is put on the effect of heat treatment on the mechanical properties of the Alloy. The gold Alloy was based on the ternary system of Au−Pt−Zn with a nominal composition of 86Au-11Pt-1.5Zn-0.5In-0.7Rh-0.2Fe-0.1Ir (wt.%). Both the hardness and tensile strength of the as-cast Alloy can be significantly improved by heat treatment at 980°C for 15 min followed by bench cooling, but can't be raised by conventional solution treatment followed by ageing. The strengthening could be attributed to homogenization of microstructure and Alloying elements and precipitation of new fine particles. It is suggested that the cast framework of the present new Pd-free Alloy could be heat treated before actual firing, and this will improve the processing properties of the Alloy during firing.

Bruno Henriques - One of the best experts on this subject based on the ideXlab platform.

  • experimental evaluation of the bond strength between a cocrmo Dental Alloy and porcelain through a composite metal ceramic graded transition interlayer
    Journal of The Mechanical Behavior of Biomedical Materials, 2012
    Co-Authors: Bruno Henriques, Michael Gasik, Delfim Soares, F S Silva
    Abstract:

    Abstract Objectives The purpose of this study was to evaluate the shear bond strength between CoCrMo Dental Alloy and porcelain restorations by application of different metal–ceramic transitional interfaces aiming at improvement of the bond strength and fracture tolerances. Methods Several metal–ceramic specimens with different composite interlayers were produced. The interlayers consisted of metal/ceramic composites with different metal volume fractions (20 M; 40 M; 60 M; 80 M). The metal–ceramic bond strength as well as the fracture strength of the composites and monolithic base materials were assessed by the means of a shear test performed in a universal test machine. The interfaces of fractured and untested specimens were examined by the means of optical microscopy. The microstructures of monolithic base materials were analyzed using SEM/EDS. The elastic and inelastic properties of the homogeneous compositions were additionally evaluated using dynamic mechanical analysis. Results The bond strength results obtained for metal–ceramic gradated specimens were the highest (261±38 MPa) for 40 vol% metal in the interlayer [40 M] vs. 109±27 MPa for a direct metal–ceramic joint. The Young's moduli and the fracture resistance of the composites revealed an increasing trend for increasing metal contents. Significance This study shows that a graded transition between metal and ceramic, provided by a metal/ceramic composite interlayer, is regarded for an increase by 2.5 times in the bond strength between the two materials relative to conventional sharp transitions. The elastic modulus of the composites used as interlayers might be very reasonably approximated by a micromechanical model.

  • microstructure hardness corrosion resistance and porcelain shear bond strength comparison between cast and hot pressed cocrmo Alloy for metal ceramic Dental restorations
    Journal of The Mechanical Behavior of Biomedical Materials, 2012
    Co-Authors: Bruno Henriques, Delfim Soares, F S Silva
    Abstract:

    Abstract Objectives: The purpose of this study was to compare the microstructure, hardness, corrosion resistance and metal–porcelain bond strength of a CoCrMo Dental Alloy obtained by two routes, cast and hot pressing. Methods: CoCrMo Alloy substrates were obtained by casting and hot pressing. Substrates’ microstructure was examined by the means of Optical Microscopy (OM) and by Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). Hardness tests were performed in a microhardness indenter. The electrochemical behavior of substrates was investigated through potentiodynamic tests in a saline solution (8g NaCl/L). Substrates were bonded to Dental porcelain and metal–porcelain bond strength was assessed by the means of a shear test performed in a universal test machine (crosshead speed: 0.5 mm/min) until fracture. Fractured surfaces as well as undestroyed interface specimens were examined with Stereomicroscopy and SEM-EDS. Data was analyzed with Shapiro-Wilk test to test the assumption of normality. The t-test ( p 0.05 ) was used to compare shear bond strength results. Results: Cast specimens exhibited dendritic microstructures whereas hot pressed specimens exhibited a typical globular microstructure with a second phase spread through the matrix. The hardness registered for hot pressed substrates was greater than that of cast specimens, 438±24HV/1 and 324±8HV/1, respectively. Hot pressed substrates showed better corrosion properties than cast ones, i.e. higher OCP; higher corrosion potential (E corr ) and lower current densities (i corr ). No significant difference was found ( p 0.05 ) in metal–ceramic bond strength between cast (116.5±6.9 MPa) and hot pressed (114.2±11.9 MPa) substrates. The failure type analysis revealed an adhesive failure for all specimens. Significance: Hot pressed products arise as an alternative to cast products in Dental prosthetics, as they impart enhanced mechanical and electrochemical properties to prostheses without compromising the metal–ceramic bond strength.

Jiang Wu - One of the best experts on this subject based on the ideXlab platform.

  • evaluation of mechanical properties and porcelain bonded strength of nickel chromium Dental Alloy fabricated by laser rapid forming
    Lasers in Medical Science, 2010
    Co-Authors: Zhongyi Wang, Xiaoming Zhao, Jiang Wu
    Abstract:

    The aim was to evaluate the mechanical properties and porcelain bonded strength of nickel–chromium (Ni–Cr) Dental Alloy fabricated by laser rapid forming (LRF). The tensile properties and porcelain bonded strengths of LRF Ni–Cr Dental Alloy were evaluated by tensile tests (five specimens per group) and three-point bending tests (ten specimens per group). The same tests for the cast Ni–Cr Dental Alloy were used as for the control. The microstructure and the bonding interface of the metal substrate to porcelain were analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The tensile strength of LRF Ni–Cr Dental Alloy (840 MPa) was superior to that of the cast Ni–Cr Alloy (670 MPa), but the ductility had decreased. The porcelain bonded strength of LRF Ni–Cr Dental Alloy was 44.7 MPa, which was also superior to that of the cast Ni–Cr Dental Alloy (41.6 MPa). According to analysis by Student’s t-test, the porcelain bonded strengths of the Ni–Cr Dental Alloy presented statistically significant differences between the groups of LRF and cast Alloy (P < 0.05), but the porcelain bonded strengths were all above the acceptable value required by the International Organization for Standardization (ISO) standard 9693 (25 MPa). The coefficient of thermal expansion (CTE, mean value of five specimens) of LRF Ni–Cr Dental Alloy (14 × 10−6°C−1) was higher than that (13.7 × 10−6°C−1) of the cast Ni–Cr Dental Alloy. Both LRF and cast Ni–Cr Dental Alloy had positive Δα, not exceeding the maximum difference (1 × 10−6°C−1) in CTE. SEM and EDS results showed that all the specimens measured for porcelain bonded strength and prepared from the LRF and cast Ni–Cr Alloy exhibited a mixed mode of cohesive and adhesive failure. Evaluation of the mechanical properties and porcelain bonded strengths of LRF Ni–Cr Alloy revealed that both superior tensile and porcelain bonded properties can be obtained. With improvement of the technique, it is hoped that the LRF Ni–Cr Dental Alloy could be a good alternative to the conventional cast Ni–Cr Dental Alloy in the future.