Basic Research Of ZrO₂/Al₂O₃ Nanoceramic Composite For Dental Application

The development of dental prosthetic materials go through from the variant teeth,animal teeth,metal material,resin material and procelain.The colour and figure of dental ceramic prosthetic materials were similar to natural tooth.Besides,ceramic prosthetic materials have the advantages that other materials don't have,such as compact texure,good wear resistance,smooth surface,good biocompatibility and security.So ceramic prosthetic materials become the popular materials for false tooth.Dental ceramic materials were divided into metal-porcelain and porcelain in recent application.Dental Ceramic Alloys was used for metal button of porcelain fuse metal(PFM) restoration.PFM restoration was popular for dentition defect and tooth defect,which has the advantages of toughness and intensity of metal and beauty and good resistance of porcelain.This technology have developed quickly since 1950,it was introduced in our country in late 1980,and it become the major method for dental repair. The indications of metal-porcelain was very wide.Many situation were suitable for metal-porcelain,such as bad colour tooth,abnormal and torsion,and so on.Metal-porcelain was divided by ceramic powder and metallic inside conolar,it has thirty kinds more or less to choose.Most of them were from German (vita,vita3d,wieland) Japan and switzerl.They have their own different characters,but they can satisfy the request of dental function.The difference between them were esthetics.The colour of German vita3d was more perfect and transparent,it was more close to natural tooth.The colour of Japan tooth powder was more sutiable for easterner skin and tooth.The difference was hard to distinguish by people eyes.The quality difference between different metal-porcelain lied with alloy component of metallic inside conolar.There were few ten kinds of alloy to choose,and they can reduced to two types,which were common metal-porcelain and nobal metal-porcelain.The major component of common metal-porcelain was Cr-Ni Alloy,it was the most popular metal-porcelain because of economy.The defect of Cr-Ni Alloy was poor corrosion resistence and inadequate stable in the complicated Oral electrolytes and Acid-base Environment.The gum edge would changed black,red swelling,hemorrhage and shrink after severage year,which affect the beauty and health of tooth.So less doctor and patient choose common metal-porcelain overseas,common metal-porcelain also included freeBeryllium alloy and Titanium alloy.The physical and chemical property can satisfy a definite request,but it can not reach the best effect of nobal metal-porcelain.Gold-porcelain was the most typical roast Porcelain tooth.It showed good corrosion resistence,good ductibility performance,good biocompatibility,hard to oxide or precipitate,firm adhesion with porcelain powder and tooth cervical would not chang colour.Most occidental patient choose gold-porcelain,but the price is several times higher than common metal-porcelain.The nobal metal-porcelain also included palladium gold and platinum gold,they were more cheapper than gold-porcelain and had high ratio performence and price.The PFM tecnology can save the intensity problem,but the complex tecnics,poor aesthetic effect,procelain brittleness and bad adhesion with metal affect the long-term clinical effect.More over the Cr-Ni Alloy was likely to dissolve poisonous elements for long time use,which would do damage to tissues and organs.Compared to metal-porcelain,full porcelain showed good biocompatibility and the colour was semilar to natural tooth.It regains more and more dental patients favour. Zirconia-Toughening-Alumina ceramics was the typical full porcelain restoration.The intensity and toughness of it were 1200MPa and 16MPa·m^1/2 more or less.ZTA widely applied dental full porcelain restoration bacause of good mechanical properties,biocompatibility and good appearance.There were several kinds full porcelain restoration in the market,such as Procera Allceram,Vita In-Ceram,IPS·Empress 2 and GI·ⅡThe In-Ceram series from VITA company was the most successful restoration in clinic.In-Ceram belonged to Zirconia Toughed Alumina caramic.It possessed enough intensity for posterior tooth crown restoration.Mclaren intruduced the Dental Glass-infiltrated Zirconia/Alumina Composite ceramic,it was applied all-ceramic bridges restoration and reached satified effect.Probster studied Glass-infiltrated Alumina for all-ceramic restoration,the result showed the material can supposed frame structure because of its high bending strength,the restoration presented good marginal adaptation and perfect esthetic attribute.Suarez examined the Glass-infiltrated Zirconia caramic for posterior tooth crown restoration in clinic for 3 years,only one experiment fail,long time examination was on the way.But the existing full porcelain did not reach the widely standard of clinical application,they also had some limitations,such as inadequate intensity,complex tecnics,low toughness and so on.How to improve the toughness and shock resistance was the major problem.It was meaningful to synthesize high strength,high toughnss dental porcelain materials,expand full porcelain restoration applied areas,reduce ceramic powder and processing cost,improve the quality of porcelain restoration,Spur the applications and popularization of porcelain restoration.ZrO₂/Al₂O₃ composite porcelain has excellent biocompatibility and mechanical properties.lt is a proper dental prosthetic materials.This study prepared an excellent ZrO₂/Al₂O₃ composite precursor powder by sol method.The crystal transfomation at different hot treatment temperature and different component ratio was examined.Also the mechanical properties of porcelain prepared by sol method and mechanical mixing method was studied.The reaction mechanism between zirconia and alumina was discussed.The ZrO₂/Al₂O₃ composite podwer was prepared by sol method.The effect of the concentration of inorganic precursors,dispersing agent,drying method and pH value on sol solution were studied.The proper conditions was confirmed.The dispersion of precursor composite powder was better at pH=9.0,1wt%PEG800+PEG2000,the inorganic precursors's concentration of 0.3mol/L,n-butanol azeotropic distillation,ammonia inverse titration method.The particles was spherical and the average particle size was 30nm.The effect ofpH value,calcined temperature and ratio of ZrO₂/Al₂O₃ on the crystal was studied.The result showed:the t-ZrO₂ intensities increaseed with the pH values of sol solution and calcined temperature.Proper alumina can inhibit the growth of zirconia grain.With the relative content of alumina increased,the crystallization temperature of zirconia improved.The mechanical properties of porcelain prepared by sol method was better than that prepared by mechanical mixing method.The Sem and EDS analysis also indicates that the composition which prepareed by sol method distribution was more homogeneous.The composite porcelain of different ratio of ZrO₂/Al₂O₃ were prepared by composite powder from sol method.The composite porcelain with 50at%zirconia content has the best mechanical properties as calcined at 1450℃,the flexural strength, fracture toughness and hardness were 786MPa,8.3MPa·m^1/2 and 14.2GPa.It can satisfy the clinical treatment request.The surface morphology and fracture characteristics were examined by SEM and XRD.The results showed that the grains of zirconia and alumina were small and combined tightly.Zirconia stress-induced phase transformation toughening effect plays an important role in improving the composite material fracture toughness.The fracture mode of the composites was mainly intracrystalline fracture.The results of heamolysis-test were negative in either of material.All the grades of cytotoxicity were 0-I.Nano ZrO₂/Al₂O₃ composite ceramics was pveliminarily safe for dental application.In the research,the composites of ZrO₂/Al₂O₃ ceramic have fine physical, chemical properties and aesthetics effect.The bulk density is close to that of natural dental,and the strength and rigidity are higher than it.It can satisfy the mechanical property request and special application environment.