| Objective: The purpose of this study was to evaluate the influence of different grinding method of CAD/CAM pure titanium to the bond strength of CAD/CAM pure titanium and porcelain and,in order to provide experimental and theoretical basis for the clinical process of titanium-ceramic restoration.Method: 1 Specimen making 1.1 Pure titanium specimen makingDesign a three-dimensional model of 25mm×3mm×0.6mm by CAD/CAM system and transfer it to the CAM system.Then the CAM control system of machine tool cutting out of 36 pure titanium specimens experimental requirements were divided into A,B two groups randomly and each group has 18 in number.The two groups of pure titanium specimens was burnished with tungsten carbide bur at low speed under10000rpm: group A was burnished along the same direction;group B was burnished along different directions.In the process,control specimen thickness was maintained(0.5± 0.05)mm range with an electronic digital caliper.Then it was sand-blasted by the 100-μm aluminum oxide particles for 20 s,and passivated the specimens for ten minutes after rinsing by running water.All specimens were ultrasonically cleaned in the distilled water sample for three times and two minutes every time,then were made them dry fully by blotting paper.One specimen was selected randomly for scanning electron microscope analysis or observation,then eight were selected for measurement of surface roughness,nine were remained for porcelain. 1.2 Titanium porcelain specimen makingPorcelain was applied to the central 8mm area of the surface of 25mm×3mm of the rest of the pure titanium specimens.First,combination agent Ti-Bond was coated immediately with glass rod after the specimens were dried fully,which were sintered according to the programs that the manufacturers provided.Second,sheltered ceramic was coated by two steps-method with glass rod also and kept the thickness 0.1mm±0.01 mm.Third,dentin porcelain was coated and burned according to the manufacture instruction.Then,dress the porcelain body with the grinding machine and control the size of it in(8±0.1)mm×(3±0.1)mm×(1.1±0.1)mm range.Finally,all of the 18 specimens were ultrasonically cleaned in distilled water and glazed.The process of specimen preparation was completed.One specimen selected from each group was polished on the lateral side for scanning electron microscope analysis or observation,the rest were ready for three point bending test. 2 Measurement of the roughness of the pure titanium surfaceAfter grinding and sand-blasting,the roughness of surface of the specimens was measured by a surface roughness tester and every sample were measured three times,and the mean of the three roughness values was considered as the surface roughness value of the specimen(Ra). 3 Scanning Electron Microscope observationsThe specimens were cleaned in anhydrous alcohol and were made them dry fully,then place them in the sample table and measured surface were sprayed with gold powder.(1)the pure titanium specimen: Observe the surface texture and residual contaminants of the titanium specimen.(2)the titanium porcelain specimen: Observe the morphology and structure of the surface of porcelain with titanium. 4 Three point bending testAccording to the ISO9693 standard,with ceramic body side down,the porcelain sintered titanium porcelain specimens were placed in the universal testing machine which have two supporting points.The two supporting points were apart from 20 mm.The radius of curvature of supporting points and pressure heads were 1.0mm.Vertical pressure was applied in the center of corresponding titanium ceramic body load at the speed of 1.0mm/min until one end of the titanium matrix and ceramic interface crazed,and recorded the fracture force values--Ffail(N) at the fracturing moments.Then calculated the bonding strength of titanium-ceramic by formula rb=k?Ffail. 5 Statistical analysis:The roughness value of the specimens surface(Ra) and three point bending experimental results statistics were analyzed with SPSS13.0 statistical analysis software.Paired-samples t-test was chosen if the dates were normally,rank sum test was selected if the dates were not normally dismissed.The test level was α=0.05.Result:1 Eye observation the two groups of titanium specimensGroup A: The surface is rough,uneven,and the texture is regular,and protrusions and depression that is more deeper alternately exist.Group B: The surface is rough,and the texture is irregular and crossed in different directions,and the center of the texture is depressed,and the depression is shallower.2 The Measurement of the roughness of the pure titanium surface: The mean value of surface roughness of group A is(3.04±0.45)μm,the mean value of surface roughness of group B is(1.39±0.14)μm.Experimental data were analyzed with SPSS13.0 statistical software which showed two sets of data were normal.Paired-samples t-test showed there were statistically significant differences between A and B groups on the roughness value of the surface(P﹤0.05).3 Scanning Electron Microscope observations of two groups of pure titanium specimens that were ground and sand-blastedGroup A: The surface is uneven and has long cracks.The edge of the specimens is not smooth with some short of apophyses.There were less aluminum oxide particles on the surface of the specimen.Group B: The surface is uneven but has more short cracks,the edge of the specimen is more not smooth with more slender apophyses on the edge.There were more aluminum oxide particles on the surface of the specimen.4 Scanning Electron Microscope observations of titanium porcelainsGroup A: Titanium and porcelain combined closely.Porcelain which broke into metal was anchored chimeric without obvious pores;the surface of the metal at the junction is uneven.Group B: Titanium and porcelain combined closely,but the surface of the metal at the junction is more smooth.Titanium-ceramic bonding interface has a number of different sizes of pores.5 The results of three-point bending test: Group A Bond strength of was(45.02±1.81)MPa;group B Bond strength of titanium porcelain was(40.40± 1.39)MPa.Experimental data were analyzed with SPSS13.0 statistical software which showed that two sets of data were normal.Paired-samples t-test showed there were statistically significant differences in A,B two groups of the titanium-ceramic bonding strength(P﹤0.05).6 Eye observation of separation of titanium porcelain interfaceGroup A: The surface of metal titanium and porcelain is grey,and the surface of titanium shows a small amount of sheltered ceramic.Group B: The porcelain can completely strip from the titanium,and the surface of metal titanium and porcelain is grey,and the surface is smooth.Conclusion:1 The bonding strength of porcelain to CAD/CAM pure titanium which was ground along same direction is greater than porcelain to CAD/CAM pure titanium which was ground along different directions and the difference was statistically significant.2 In a certain range,with the roughness of pure titanium surface becoming more bigger,the bond strength of porcelain to CAD/CAM pure titanium is more stronger.3 The bond strength of porcelain to CAD/CAM pure titanium which was ground along the same and different directions is more than 25MPa(the standard of ISO) which meets the requirements of clinical application. |
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