Nickel based alloys

1. Nickel basedalloys

2. Introduction: - nickel is characterised as allergen, but it has a important place between the dental alloys - the statistics tell, that the hypersensitiveness is around 10% of population

3. Introduction: • 1/ Nickel as Ni-Cu alloys is in the coins • when the coin has a lot of nickel has grey or white- grey color • 2/ nickel as a Fe-Ni- Cr alloys is the part of surgical and others dental instruments • - The cause of hypersensitivity is content of chrom • when is the higher content of chrom , so is the fortior passive layer on surface of alloy • passive layer protects alloys before corrosion and so make the better biocompatibility • although nickel can make hypersensitivity reaction, was assigned standard ISO norma 6871-2

4. Introduction:

5. The development of Ni-Cr alloys: • at first was nickel used in China as a means in payment • at 1751 year was isolated pure nickel by the Alexander Cronstedt • at 1775 y. was first described the properties by Torben Bergman. He suggested on the properties likeness of ferrum and nickel • at  18. century was used nickel as a means of payment in Europe • in the nature is nickel bonded on sulphur, arsenum and antimony • 60% of this naturally nickel is swalloved in producing of steel • nickel has a grey-white or white-yellow color with a good optical properties

6. Chemical characteristic of pure nickel: • the melting temperature of pure nickel is 1455°C • to the temperature 360°C is this metal as magnetic (similar as a ferrum) • pure nickel is malleable metal with a cold plastic deformation, but very strong • chrome as a one part of these alloys was at first described at 1797 year by Luis Vauquelin • it is important for better mechanical properties and higher protect before corrosion • the binary alloy Ni-Cr was at first described at the 1906 year • it has a high resistance before corrosion and before oxidation

7. Chemical characteristic of nickel alloys: • the melting temperature of Ni-Cr alloy is 1345°C • from chemical view, these alloys are not as a monophase alloys, not homogenous alloy • chrome makes some makromolekules, which have a different content of chrome at variable temperature . By the setting are rising some crystals, which are not equally disperse by the diffusion • from this results different energetic layers , different energetic potential and they are the base for galvanic voltage • chrome supports creation of passive layer, which is important for higher resistance before corrosion • for betterment of passive layer are appending others elements as a molybdenum, wolfram, carbon, nitrogen

8. Chemical characteristic of nickel alloys – dental protheses: • the melting temperature at these alloys is between 1250-1350 °C • the casting temperature is about 100°C higher than melting temperature (for the better properties by the casting) • by the casting of dental reconstructions make convergence important role for complete filling casting form

9. Physical properties: • the density of Ni je 8,9 g/cm3, Cr 7,1 g/cm3 a Mo 10,2 g/cm3 • the density of alloys is decreased when is higher content of chrome, and addition of molybdenum makes increase density of alloys • according to using these alloys, it is burning in ceramic, is important to evaluate linear thermal expansion of alloy and burning temperature of ceramic ( linear thermal expansion must be zero or minimally)

10. Mechanicalproperties: • dentalreconstructions are exposed by themastication and fromitresultsmechanicaltensionanddeformation • the state ofinternalmechanicaltensionisdepend on: • 1/ mechanicaltension in processing • 2/ thermaltensionisdepend on thermaldifferentbetween hot and cooltemperature by theconsummation • forstabilisationisusedadditionas a alluminium or titanium • so canrisethedistributedellementaryNi-Tiparticleswhichcanincreaseddeformatingresistance and so canstrenghtenstructureofalloys • resistancebeforeabrasionisdepend on hardnessafterVickers or Brinell

11. Joining and welding Ni-Cr alloys: • - making of quality metallurgical joint needs absolutelyv pure surface • - for it is important to remove surface layer using by anhydrous borax as a salt of boric acid • after it can be applied solder, which connects two parts of alloy

12. Joining and welding Ni-Cr alloys: • - the solder must have the melting temperature about 100°C decreased than is the melting temperature of origin alloy ( for protect of origin alloy) • a chemical composition of solder is similar as a composition of origin alloy • from it results, that the place of connection is not very different from whole cast • the different composition solder and origin alloy produces the base for galvanic current

13. Corrosion of nickel alloys: • the nickel corrosion in water is deped on pH value and electric potential • other patrs of nickel alloys as a molybdenum and chrome protect the nickel alloys by the passive layer on the surface • when the Ni-Cr alloys have a ISO standard, the content of chrome must be minimally 25% and molybdenum 19%

14. Biocompatibility of Ni-alloys: • - metalic ions, which are released from surface, are reacted with surrouding soft tissue, with saliva, enzymes, bacteriums and with dental plaque • metal cations react with anions surrounding medium. So they can make macromolekules. So elementary parts from alloys are trasported to the various parts of body. • solubile compound of Ni-alloys are absorbed very quick • Ni-alloys are not only in dental protheses, but they are normal part of some food

15. Biocompatibility of Ni-alloys: • Ni is absorbed from air, food and from drinks • daily it is about 300-600 microgramms • biological half time of resorbtion is about 11-24 hours • some macromolecules with mutagenic, toxic and carcinogenic can incorporate to the structure of DNA and so initiative damage

16. Ni dental alloys and dental prax: • practicaladvantages: • ultrahighresistancebeforecorrosion • minimalcytotoxicity on cellulatrlayer • flatthermalconductance • high modul of elasticity • highresistance to thedraw and press • thehardnessis 180 HB • longcooling interval • flatvolumecontraction • compatibilitywith a bondforceramic

17. Zliatiny Ni-Cr-Mo v zubolekárskej praxi: • indications: • metaloceramics • fixed veneering reconstruction • metal framwork removable denture

18. END.