Nickel based alloysNickel based alloys

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

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

 

Introduction:

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

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

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

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

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)

Mechanical properties:

- dental reconstructions are exposed by the mastication and from it results mechanical tension and deformation

- the state of internal mechanical tension is depend on:1/ mechanical tension in processing2/ thermal tension is depend on thermal different between hot and cool temperature by the consummation

-for stabilisation is used addition as a alluminium or titanium-so can rise the distributed ellementary Ni-Ti particles which can increased deformating resistance and so can strenghten structure of alloys- resistance before abrasion is depend on hardness after Vickers or Brinell

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

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

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%

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

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

Ni dental alloys and dental prax:

Zliatiny Ni-Cr-Mo v zubolekárskej praxi:

- indications:

- metaloceramics

- fixed veneering reconstruction

- metal framwork removable denture

END.