Effect of retorque on loosening torque of prosthetic screws under two levels of fit of implant-supported dentures.
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Corrosion properties of Ag-Au-Cu-Pd system alloys containing indium.
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In this study, the corrosion resistance of Ag-Au-Cu-Pd system alloys consisting of 5 or 10 mass% indium was evaluated. Levels of element release and tarnish were determined and electrochemical measurements performed. Results were compared with those for commercial silver-palladium-gold alloy. In terms of electrochemical behavior, the transpassive potential of these experimental alloys was 168-248mV. Experimental alloys with 25 mass% Au showed similar corrosion resistance to control gold-silver-palladium alloy. Amount of released elements was 14-130microg/cm(2) at 7 days, which is in the allowable range for dental alloys. Addition of indium to Ag-Au-Cu-10mass%Pd system alloys was effective in increasing resistance to tarnish and alloys containing 10 mass% of indium showed a minimal decrease in L(*) values after immersion. These findings indicate that 25Au-37.5Ag-15Cu-10Pd-2Zn-10In-0.5Ir alloy is applicable in dental practice. (+info)
Chemical analyses of hydroxyapatite formation on SAM surfaces modified with COOH, NH(2), CH(3), and OH functions.
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Hydroxyapatite formation was examined at the surface of self-assembled monolayers (SAMs) modified with four functional groups, -COOH, -NH(2), -CH(3), and -OH. For COOH-SAM and NH(2)-SAM, scanning electron spectroscopic observation showed that flake-like sheet crystals covered the whole wafer and small broccoli-like crystals were observed occasionally on the flake-like crystal base layer. For CH(3)-SAM and OH-SAM, no flake-like sheet crystals were observed; broccoli-like crystals were observed in a dispersed manner for CH(3)-SAM, but in localized spots for OH-SAM. X-ray diffraction patterns showed a strong apatite pattern oriented toward the c-axis direction for COOH-SAM. ESCA analysis revealed distinct Ca, P, O peaks for COOH-, NH(2)-, CH(3)-, and OH-SAM. Surface plasmon resonance (SPR) analysis indicated that during the supply of supersaturated calcium phosphate solution, the deposition of precipitates increased monotonically with time for COOH-SAM, increased slightly for NH(2)-SAM, but little increase in deposition was detected for CH(3)-SAM and OH-SAM. (+info)
Reliability of metalloceramic and zirconia-based ceramic crowns.
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Study of corrosion of combinations of titanium/Ti-6Al-4V implants and dental alloys.
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Metal ions released in 1% lactic acid solution from combinations of titanium fixtures with superstructures made of dental precious metal alloys (dental alloys) and titanium and differences based on the fixing method were investigated. In combinations of titanium with dental alloys, the level of Ti release was influenced by micro-structure of titanium: it was lower when the grain size was smaller. In titanium-titanium combinations, differences in the micro-structure of metal also markedly influenced the dissolution: the level of release increased when the micro-structure of titanium was different. The Ti and V release levels were higher in combination with titanium alloy and titanium than with titanium alloy and dental alloys. Regarding the superstructure-fixture fixing method, the level of Ti release was significantly lower in cement than in direct fixation. (+info)
New glass polyalkenoate temporary cement for cement-retained implant restoration: evaluation of elevation and retentive strength.
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The purpose of this study was to evaluate four luting agents for cement-retained implant restorations in two aspects: post-cementation elevation of the superstructure and the retentive strength before and after thermocycling and mechanical cycling. The four evaluated luting agents were: new glass polyalkenoate hard-type (GH) and soft-type (GS) cements, polycarboxylate hard-type (HH) and soft-type (HS) cements. Elevation and retentive strength were measured using a CCD laser displacement sensor and a universal testing machine respectively. Elevation increased in this order: GH, GS, HH, and HS. Thermal and mechanical stresses significantly decreased retentive strength, and the mean values exhibited by GH were significantly higher than the other luting agents. The novel glass polyalkenoate cements (hard- and soft-type) experimentally prepared in the present study augured well as luting agents by virtue of their reduced film thickness and their excellent post-cementation retention and elevation. (+info)
Evaluation of thiouracil-based adhesive systems for bonding cast silver-palladium-copper-gold alloy.
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This study aimed to evaluate the effect of adhesive systems based on a thiouracil monomer on bonding to silver-palladium-copper-gold (Ag-Pd-Cu-Au) alloy (Castwell M.C.12). Disk specimens were cast from the alloy and then air-abraded with alumina. The disks were bonded using six bonding systems selected from four primers and three luting materials. Shear bond strengths were determined both before and after thermocycling. Bond strength varied from 2.7 MPa to 32.0 MPa. Three systems based on a thiouracil monomer (MTU-6) showed durable bonding to the alloy, with post-thermocycling bond strengths of 22.4 MPa for the Metaltite (MTU-6) primer and Super-Bond, a tri-n-butylborane (TBB) initiated resin, 9.0 MPa for the Multi-Bond II resin, and 8.1 MPa for the Metaltite and Bistite II system. It can be concluded that a combination of thiouracil-based primer and TBB initiated resin is effective for bonding Ag-Pd-Cu-Au alloy. (+info)
Evaluation of the static frictional coefficients of Co-Cr and gold alloys for cone crown telescope denture retainer applications.
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The static frictional coefficients (SFC) of a Co-Cr and a gold alloys were evaluated for the application of a cone crown telescope system in removable prosthesis. The SFCs of the Co-Cr alloy were lower than those of the gold alloy. The SFC of the gold alloy decreased by annealing at 85 degrees C in air and was restored by re-polishing, although that of the Co-Cr alloy was stable irrespective of the annealing. The XPS analysis revealed the formation of a surface oxide layer on the gold alloy after annealing. The decrease in the SFC of the gold alloy may have been caused by the formation of an oxide layer on the surface due to annealing. The relationships among such factors as the retentive force, SFC and cone crown angle indicate that the angle of the Co-Cr alloy should be lower than that of the gold alloy based on the Korber's model. (+info)