Nickel 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

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 °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 processing 2/ 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 microgramms - biological half time of resorbtion is about 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: - practical advantages: - ultra high resistance before corrosion - minimal cytotoxicity on cellulatr layer - flat thermal conductance - high modul of elasticity - high resistance to the draw and press - the hardness is 180 HB - long cooling interval - flat volume contraction - compatibility with a bond for ceramic

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

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