| Objective: Loding-test was carried out to compare thestrength of nano-ceramic and traditional-ceramic. Scanningelectron microscope (SEM) was used to analyze themicrostructure of the ceramic .The relationship betweendifferent porcelain thickness and strength was discussed .Theresults were expected to provide effect experimental refrence tothe clinical application of nano-ceramic.Methods: 1 Models preparation:a metal die of simulatingcrown core is produced with precision machine,Totally 32(in 8groups,A to H metal-ceramic crown modles,were conventionallyproduced.Group A-D were traditional ceramic with differentthickness 0.5mm, 1.5mm, 2.5mm, 3.5mm; group E-H werenano-ceramic with different thickness 0.5mm, 1.5mm, 2.5mm,3.5mm. 2 The surface feature of the tested specimens wasobserved by the scanning electron microscope (SEM). 3 WithInstron testing machine, vertical force of 300N was loaded onocclusal surface of each model for 5 minutes. 4 Changes ofsurface structure were observed with SEM after loading. 5 WithInstron testing machine, destruction test on each modle wasperformed to test fracture force values. 6. Each modle'sstructure in fracture section was observed with SEM.Results: 1 Metal-ceramic crown surface microstructure:ingroup A,a few small cracks and crystals of different sizescattered,pores densely distributed; in group B,no obviouscracks was visible,small pores evenly scattered; In group C, noobvious cracks was visible,small pores and crystals evenlyscattered; In group D,the surface was uneven,many cracks andpores widely scattered,crystal with long diameter exist in allspecimens,the large crastal gathered fromed as island; in groupE,many cracks were shown in all specimens.Apparent poresgathered.no obvious crystal was visible; in group F and G,nocracks and crystals was shown,small pores evenly scattered; ingroup H,no cracks and crystals were shown,pores were fewerthan in group D.2 The surface microstructure after loading:in group A ,largequantity of pores densely distributed; in group B, no obviousdifference was shown; in group C,there were few pores insurface; in group D,new cracks were found,pores denselydistributed; in group E,new cracks were found widelydistributing.Cracks with diameter of 35μm was occasionallyseen. Pores densely distributed; in group F and G, no obviousdifference was shown; in group H, there were few cracks insurface.3 Means of strength obtained from destruction test were asfollows(unit:Kg):Group A 103.88±4.52,Group B 190.42±3.46,Group C 186.69±3.85,Group D 141.67±7.68,Group E80.99±5.73,Group F 223.13±2.69,Group G 216.48±5.61,GroupH 166.81±4.67.Analysis of variance(ANOVA)results indicatethat there were significant difference of destruction test valueson models with defferent thickness(P < 0.01).multiplecomparison results indicate that significant difference indestruction test values exist between group A and B, group Aand C, group A and D, group Band D, group C and D, group Eand F, group E and G, group E and H, group F and H, group Gand H.( P<0.01); no significant difference between group Band C, group F and G(P>0.05).T-test results indicate that therewere significant difference of destruction test values on modelsbetween strength of nano-ceramic and traditional ceramic(P<0.01).4 The fracture sections structure: in group A, fracture sectionswere uneven, pores and crack densely scattered; in group B,structure of fracture sections was dense. no obvious cracks wasfound,few pores widely distributed; in group C, fracture sectionswere even, no obvious cracks was found,few pores withdifferente diameter and regular shape were shown, large numberof crystals with 3μm diameter scatterly distributed; in goup D,fracture sections were uneven,small peelings are shown,manyspherical pores with differente size densely distributed; in groupE, fracture sections were loose,small particle was found aroundcracks,large number of pores with different size denselydistributed; in group F and G,fracture sections were even,fewpores scattered,no obvious cracks was visible; in group H,...
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