| Objective: The purpose of this study was to evaluate the bond strength of nano-ceramic and four commercially available alloys. The results were expected to provide theoretical basis for clinical application of nano-ceramic.Methods:1 Specimens Preparation: Forty-four rectangular wax patters (25×3×0.5mm) were divided into A, B, C and D four subgroups: Ni-Cr alloy group, Co-Cr alloy group, little-Ti-containing alloy group, Au-Pt alloy group. There were eleven specimens in each group. Ten specimens were used for three-point bending test. One specimen was used for scanning electron microscopy with energy-dispersive spectrometry. A wax sprue was attached perpendicular at one end of the patters. Then degreased by soap water, dried by clean air, embed by phosphate. The wax patterns were eliminated by heat and replaced by each kind of alloy, using the investment thermal expansion technical. The hot rings were allowed to heat-soak for 15 minutes in air at room. Elimination of sprue, nodule and separation of metallic strips were performed with the aid of carbide disks at low speed. Surfaces of the specimens that would receive the ceramic layer were air abraded with airborne particle abrasion with 100-μm aluminum oxide. This was done at an angle of 45°for 20 seconds, and from a distance of approximately 2 cm under 0.5 bar pressure. All specimens were then ultrasonically cleaned in distilled water for five minutes twice and allowed to dry at room temperature. An area of 8×3mm was marched on the specimens for ceramic. All opaque bonding dental ceramic (0.1mm) were fired by using twice-fire technique. Thickness of the denial dentine ceramic layer was controlled by rule of thumb, sintering in the same porcelain furnace following the respective manufacturers'recommendation. All specimens were burnished by the same dental lathe at the same speed, then flattened the surfaces in the same direction by grinding on 240, 400, 600, 800, 1000, 1200, 1500-grit water sand papers, Thickness of the dentin ceramic (1mm) was standardized in an electronic caliper. After self-glazing and ultrasonic cleaning by distilled water, all the specimens were prepared. The metal-ceramic combinational interfaces of the one specimen which was selected stochastically from each group were polished.2 Three-point bending test: The flexural strengths were obtained by a three-point bending test in a universal testing machine. The specimens were centered and supported on two symmetrically space balls (span, 20mm; diameter, 1mm). Load was applied at the center of the specimen through the tip (diameter, 1mm) of a piston at a speed of 1mm/min in air at room temperature. Measuring 10 specimens of each specimen PFM layer at the end of the dissection occurred when fracture force Ffail (N). Stripping/fracture - starting bond strength rb by the following formula: rb=k·Ffail, the formula: k can be found in YY0621-2008 according to the thickness and elastic modulus of metal, Ffail was from three-point bending test force value.3 Energy disperse spectroscopy analysis:The prepared specimens were bonded to the sample stage, to be measured place face up on parallel to it. Then metal-ceramic combinational interface were examined using scanning electron microscopy with energy disperse spectroscopy (EDS) to observe line scans of elements in each group.4 All values were analyzed by SPSS13.0 statistical analysis software. P values less than 0.05 were considered to be statistically significant in all the tests.Result:1 The result of three-point bending test (table 1): A (Ni-Cr alloy group): 30.77±2.25MPa; B (Co-Cr alloy group): 32.88±3.66 MPa; C (little-Ti-containing alloy group): 41.06±2.93MPa; D (Au-Pt alloy group): 47.83±4.11MPa. One-way analysis of variance (table2,3) was shown that, besides the bond strength between Ni-Cr alloy/ nano-ceramic and Co-Cr alloy/ nano-ceramic was no statistically significant difference (P>0.05), there was statistically significant difference between the rest of any two groups(P < 0.05). 2 The result of Energy-dispersive spectrometry showed that (Fig. 912) : Si, K, Al and O dispersing from ceramic to interface while metallic elements from metal to interface and lastly. Ni-Cr alloy group: Ni,Cr,Mo and Mn distributed throughout the Ni-Cr alloy and then terminated at the interface. Concentrations of O, Ni and Mo were seen in interface. Co-Cr alloy group: Co, Cr, Mo, Ce and Wu distributed throughout the Co-Cr alloy and then terminated at the interface. Concentrations of O, Co and Ce were seen in interface. Little-Ti-containing alloy group: Ni, Cr, Ti and Ce distributed throughout the little-Ti-containing alloy and then terminated at the interface. Concentrations of Ce were seen in interface. Compared with Ni-Cr alloy, the peak of Ni was not seen. Au-Pt alloy group: Compared with the other three alloys, the peak of O was not seen. Au, Pt and Sn distributed throughout the Au-Pt alloy and then terminated at the interface. Concentrations of Sn were seen in interface. The amount of Pd, Ag, Ir, Ce, In and Fe was too little, we can not see clearly.Conclusion:1The experiment drew a conclusion that the bond strength of the four kinds of metal-ceramic alloys was all beyond 25MPa, the baseline of ISO.2The bond strength of nano-ceramic and Au-Pt alloy is maximum, little-Ti-containing alloy next, Ni-Cr alloy, Co-Cr alloy minimum.3 Ni-Cr alloy and Co-Cr alloy are similar for nano-ceramic about their bond strength.
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