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Tarnish and corrosion /certified fixed orthodontic courses by Indian dental academy
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Tarnish and corrosion /certified fixed orthodontic courses by Indian dental academy

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The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.

Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
Dental implants courses.for details pls visit www.indiandentalacademy.com ,or call

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  • 1. Tarnish and Corrosion INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  • 2. Metals do not exist in their pure form naturally. They are always bound with non-metals and exist as oxides and sulfides. So, to produce pure metals a great deal of energy is required. So pure metals exist in high energy form and try to return to their normal combined state. Process by which this occurs is corrosion. www.indiandentalacademy.com
  • 3. What is tarnish ? It is a surface discoloration on a metal or even a slight loss or alteration of the surface finish or luster. www.indiandentalacademy.com
  • 4. What is corrosion ? It is not the surface discoloration but actual deterioration of a metal by reaction with environment. www.indiandentalacademy.com
  • 5. Tarnish is often a forerunner of corrosion. H2S /NH4S2 Ag, Cu, Hg O2& Cl Amalgam S Casting alloys containing silver www.indiandentalacademy.com
  • 6. Corrosion Dry (chemical) Wet (electrolytic/electrochemical) galvanic stress Crevice/concentration cell electrolyte oxygen www.indiandentalacademy.com
  • 7. Chemical/dry corrosion Metal reacts to form oxides and sulfides in absence of electrolytes. Eg- silversulfide in silver alloys oxidation of amalgam www.indiandentalacademy.com
  • 8. Electrolytic corrosion Requires presence of water and other fluids www.indiandentalacademy.com
  • 9. Anode – metal which looses electrons - forms +ve ions - undergoes oxidation reaction M0 M+ + e- Cathode-metalwhichacceptselectrons M+ +e- M0 www.indiandentalacademy.com
  • 10. Electromotive force series it shows the tendency of a metal to give out electrons when inserted in an electrolyte Metal with lowest EMF values corrodes metal ion Electro de potenti al Gold Au +1.50 Platinu m Pt +0.86 Silver Ag +0.80 Copper Cu +0.47 Hydroge n H + 0.00 Cobalt Co -0.28 www.indiandentalacademy.com
  • 11. Galvanic corrosion Occurs when dissimilar metals come in contact with each other Eg- amalgam in contact with gold restoration Galvanic shock Varnish application Due to heterogenous composition -impurities in any alloy -solder joints -in alloys due to difference in composition www.indiandentalacademy.com
  • 12. Stress corrosion Cold working makes the metal more reactive Metal acts as anode and corrodes. Eg- ortho wires www.indiandentalacademy.com
  • 13. Crevice corrosion/concentration cell corrosion Electrolyte concentration cell – - In metallic resto which is partially covered,the composn of electrolyte under the food debris will differ from that of saliva which can contribute to corrosion. Oxygen concentration cell – - Differences in oxygen tension in between parts of the same restoration causes corrosion of the restoration www.indiandentalacademy.com
  • 14. Protecion against corrosion Passivation Increase noble metal content Polishing restoration Avoid dissimilar metal restoration www.indiandentalacademy.com
  • 15. www.indiandentalacademy.com Thank you For more details please visit www.indiandentalacademy.com