The Effect of Recasting on the Bond between Porcelain and a Nickel-Chromium Ceramic Alloy

Objective: To study the effect of recasting on the bonding strength of a porcelain fused to a alloy, the thermal expansion coefficient and the oxide layer of the alloys of the Ni-Cr ceramic alloy.Methods: (1)Preparations of casting materials: The Ni-Cr ceramic alloys recast for 1~4 times were available respectively after the Ni-Cr ceramic alloys provided by the manufacturer having been cast 1~4 times. Before being recast again, the Ni-Cr ceramic alloys recast should be delt with sand blasting, water washing, aqua regia soaking, rinse, cutting, ultrasonic cleaning in distilled water and drying naturally in turn to be the recasting materials in the next time. (2) According to ISO 9693,the bonding strength of the porcelain fused to the nickel-chromium ceramic alloys which had been recast for 1~5 times under the circumstance of vacuum compressive casting with argon was tested in the three-point test, and the testing results were taken into statistic analysis(one-way classification ANOVA). The morphology of the specimen metal bases was observed after the porcelain layers of specimen falling completely loaded. (3) According to the requirements of the thermal expansion samples, the metal stick samples with parallel ends, the diameters(5.5±0.05)mm and the lengths(25.0±0.05)mm, were made of the Ni-Cr ceramic alloys recast for 1~5 times under the circumstance of vacuum compressive casting with argon. Then according to ISO 9693, the metal sticks were tested and their thermal expansion coefficients were available in the thermal expansion coefficient testing apparatus. And the testing results were taken into statistic analysis. (4) It was observed the surface of nickel-chromium ceramic alloys recast for 1~5 times after sandblasting, the surface and the cross-section of the oxide layer of nickel-chromium ceramic alloys after pre-oxidation in the environmental scanning electron microscope under the circumstance of vacuum compressive casting with argon.Results: (1) There presented no statistical differences in the bonding strength of the porcelain fused to the nickel-chromium ceramic alloys recast for 1~5 times (P=0.164).Porcelain layers were stripped overall without any rupture as a whole, and the surface of the specimen metal bases where the porcelain layers were stripped presented the characteristic of frosted glass under stereo microscope observation. (2) There presented no statistical differences in the thermal expansion coefficients of the nickel-chromium ceramic alloys recast for 1~5 times (P=0.384). (3) In the environmental scanning electron microscope, there presented little change on the surface of nickel-chromium ceramic alloys recast for 1~5 times after sandblasting. On the other hand, it was also no significant change on the surface of the oxide layer of nickel-chromium ceramic alloys recast for 1~5 times after pre-oxidation. There is no obvious change on the cross-section of the oxide layer of nickel-chromium ceramic alloys recast for 1~4 times after pre-oxidation. Compare with the cross-section of the oxide layer of nickel-chromium ceramic alloys recast for 1~ 4 times, there seemed slightly loose and local flawed on the cross-section of the oxide layer of nickel-chromium ceramic alloys recast 5 times after pre-oxidation.Conclusion: Under the circumstance of vacuum compressive casting with argon, there presented no statistical differences in the thermal expansion coefficients and the bonding strength of the porcelain fused to the nickel-chromium ceramic alloys recast for 1~5 times. There presented little change on the surface of nickel-chromium ceramic alloys recast for 1~ 5 times after sandblasting. It is no significant change on the surface of the oxide layer of nickel-chromium ceramic alloys recast for 1~5 times after pre-oxidation. There is no obvious change on the cross-section of the oxide layer of nickel-chromium ceramic alloys recast for 1~ 4 times after pre-oxidation. Compare with the cross-section of the oxide layer of nickel-chromium ceramic alloys recast for 1~4 times, there seemed slightly loose and local flawed on the cross-section of the oxide layer of nickel-chromium ceramic alloys recast 5 times after pre-oxidation.