| Objectives: The purpose of this study was to compare the bondstrength of porcelain–fused-to-metal(PFM)of pure titanium crowns fabricatedby computer-aided design/computer-aided manufacturing(CAD/CAM) andcasting technology, This experiment explores the effect of these two kinds ofdifferent processing technology on titanium-ceramic bonding strength. andanalyze whether the strength was related to the shape of metal coller.Provideexperimental guidance for pure titanium procelain crown edge design andprocessing methods.Methods：1Pure titanium porcelain crowns preparation: a metal die of simulatingcrown core of premolars was produced by precision instrument. Theimpression of the metal die was taken by DMG silicon rubber and the ultrahard plaster was perfused. Totally wax models of12titanium substrate crownswere fabricated by wax dipped method.All crowns were divided into A1groups and A2groups equally of which each included six samples without orwith360°metal collar. According to the pure titanium casting requirements,sprue was placed. Invested it with magnesium oxide embedded material forpure titanium, cast12pure titanium base crown with pure titanium specialcasting machine. The two groups of pure titanium specimens was burnishedwith tungsten carbide bur while mesured the thickness of base crown byvernier caliper. In the process, control every metal base crown about0.5mm.Then it was sand-blasted by the100-μm aluminum oxide particles for20s,ultrasonic cleaning with distilled water, and shock away impurities andsurface debris.Use absorbent paper to siphon the surface water and made themdry fully.Use special porcelain powder(Duceratin Kiss)of pure titaniumporcelain gradually according to the manufacturer instructions: combination agent Ti-Bond was coated with glass rod,and then uniformly coated thesurface of metal base crown which had been dry fully and sinter themaccording to the process that the manufacturers provided. Sheltered ceramicwas coated by two steps-method with glass rod and kept the thickness wasabout0.2mm which would block the metal background； At last,dentinporcelain was coated and the thickness was kept about0.9mm, which wereburned according to the manufacture instruction. All the steps such as grinding,polishing, sandblasting, passivating, distilled water cleaning and coating layershould go on continually.Another groups of12pure titanium base crown fabricated by CAD/CAMcalled B.12crowns were divided into B1groups and B2groups equally ofwhich each included six samples about0.5mm in thickness without or with360°metal collar.The process of porcetain as above.2The test of strength: six PFM crowns of each group were tested forfracture strength by universal load-testing machine.Make the loading head at aconstant rate of1.0mm/min loading on the function tip(apical)until theporcelain layer exfoliation from metal surface. Data of fracture strength wererecorded just samples fracture occurred.3Scanning Electron Microscope observations:take the largest combination of titanim-porcelain in the group of CAD/CAM and casting as the observed,spraying with gold powder to the surface to be tested. Observe the microstructure of the porcelain with titanium by scanning electron microscope.4Statistical analysis: Experimental data were analyzed with SPSS13.0statistical software. Independent-samples t-test was chosen such as datanormality and homogeneity of variance. If the data is not normal or variancenot neat, separate variance estimation(t′test) or Wilcoxon rank sum test wasselected. The test level was α=0.05.There was statistical significance ifP<0.05.The result would show as x±s.Results:1Macroscopic observation:a large area of porcelain layer stripped from the crowns.The surface of titanium base crown in CAD/CAM group was moreclean than casting group which presented a uniform layer of silver film.Itillustrated that fraction surface most occur between pure titanium basecrown and oxide film. Also, small part of fracture surface appeared inporcelain layer.2The results of Scanning Electron Microscope: the titanium-porcelaininterface feature of group CAD/CAM were tight and clear. No obvious cracksand bubbles were observed. For other groups, some holes or cracks wereobserved. The titanium-porcelain interface was not combined closely.3The strength values of PFM crowns were as follows: A11429.45±31.89N,A22182.40±26.07N;B12003.28±38.75N,B22710.33±16.66N. Experimental data were analyzed with SPSS13.0statistical software.The group of CAD/CAM and casting or collar and non-collar,s data normality and homogeneity of variance.So independent-samples t-test was chosen toanalyze the group of CAD/CAM and casting or collar and non-collar showed that there were statistically significant differences in the titanium-ceramic bonding strength (P﹤0.05).Conclusion:1The CAD/CAM technique improve the fractre strength of porcelainfused to pure Ti cast crown in comparison to that of being made byconventional methods.2A360°all-metal collar was helpful to increase bonding strengthbetween titanium and dental porcelain. |
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