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Metals in dentistry

Metals in dentistry. Libyan International Medical University. Dental amalgam Casting alloys Wrought metal wire Metals used in orthodontic Implant materials Endodontics posts. Pure gold is the noblest of all dental metals.

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Metals in dentistry

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  1. Metals in dentistry Libyan International Medical University

  2. Dental amalgam • Casting alloys • Wrought metal wire • Metals used in orthodontic • Implant materials • Endodontics posts

  3. Pure gold is the noblest of all dental metals. • It is inactive chemically, is not affected by air, heat, moisture and most solvents. • It resist tarnish and corrosion. • Its thermal expansion co-efficient is similar to that of tooth. • It is malleable (ability of a material to rolled into sheet with out fracture). • It is ductile (ability of material to be stretched with out rupturing). • Because of these properties, it’s the most ideal restorative material for preserving tooth structure in non- esthetic areas.

  4. Metals can be divided into two groups • Noble metals :-that are used in dental casting alloys are gold(Au), palladium(Pd) and platinum(Pt) • In dentistry silver is not considered as noble metal. • Base Metals:-In dental casting alloys,these metal includes titanium(Ti), nickel(Ni), silver(Ag), zinc (Zn) and others.

  5. Metal is elements that ionizes positively in solution • Metal have certain typical properties, such as: 1. Luster 2. opacity 3. density 4. strength 5. thermal and electrical conductivity

  6. Currently available direct gold can be divided into three categories:- 1. Foil (fibrous gold) 2. Electrolytic precipitate (crystalline gold) 3. Powdered gold Gold Foil • Gold foil is the oldest of all products .It has been used for thousands of years. It was probably the first form used as a dental restorative material

  7. It was used directly in the prepared cavity by compacting layer on layer with instruments called condensers ,it can be placed with hand condensers (hammering the piece into the cavity ) or with aid of an electrically operated mechanical condenser. However, these metal lacked enough strength to be used for many dental restorations such as crowns and bridge.

  8. Annealing:- It is a process of heating gold foil to remove surface impurities to make it cohensive. • Cohensive gold:- is the gold that can be weld easily with another piece of gold. Annealing gold foil immediately before use make it more cohesive ,the process involve degassing the surface by heat applied in the annealing furnace or alcohol flame.

  9. The amount of gold in an alloy can be described in several ways besides percentage • Karat is used to measure gold content in . jewelry. • Fineness, Fineness can be obtained by multiplying the percentage of gold by 10.

  10. Gold Alloys for Casting Casting: • It is a process by which a wax pattern of a dental restoration is ultimately converted into an exact replicate in metal. • Gold alloys are classified in dentistry as • Type 1:- Soft (for restorations subject to very slight stress such as inlays) • Type II:- Medium ( for restoration subject to moderate stresses such as onlay) • Type III:- Hard ( for high stress situation such as onlays ,crowns, thick veneer crowns and short span fixed partial denture.) • Type IV:- Extra hard (For extremely high stress states, such as endodontic post and cores, thin veneer crowns, long span fixed partial dentures, and removable partial dentures.

  11. Low carat gold alloys is light golden colour and has gold 40%, Palladium is not higher than 6%, Copper and silver 54%. Palladium has tarnish resistance. • White gold alloys : - Lower percentage of gold about 30%, greater amount of palladium 10-35%, silver 35-60% & copper 6-25% • Palladium acts as potent whitener, it absorbs hydrogen and other gases during melting and produce porous casting

  12. Ingredients of gold alloy • Gold:- (60-71 %) Colour, tarnish resistance and ductility • Copper:-( 11-16%) reddish appearance, improve hardness and strength, lower fusion temperature , lower tarnish resistance as well. • Silver:-(4.5-20%) hardness, strength, lower tarnish resistance • Platinum:-(0-3.5%) strength, raise fusion point

  13. Palladium:- Whitens the alloy. Alloys more than 6% palladium take on a whiter colour. • Zinc (0.5% ):- Deoxidizing element, it reduces the oxygen content (Oxygen released in solidification results in porosity) • Iridium:- Grain refiner (grains are tiny crystals of a metal seen under the microscope ). Porosity is usually seen with in and along the grain boundaries • Fine grain alloys; stronger and more ductile • Coarse grained alloys; large grains Iron,Tin,Indium:- Used with porcelain .Acts as hardening and bonding agents.

  14. Biocompatibility of alloys • Pure metals (gold and palladium ) are less toxic followed by silver, nickel and copper • Lower gold + high copper alloy- Increase cell toxicity and greater tarnish. (Palladium additions reduces copper toxicity) • Nickel-allergen alloys

  15. Soldering and Brazing • Soldering: Is joining metals at low temperature (below 450°C) • Brazing: Is joining metals at high temperatures (above 450°C) Solders • In dentistry solders are special alloys used to join metals. Soldering involves the use of flux, which is a material that cleans the alloy to be soldered and dissolves any surface oxides on the metal.

  16. For an alloy to be soldered all it's oxides must be eliminated to allow wetting and flowing of the solder on the alloy surface. • Fluxes comes in pastes, liquids and powders. • Gold based alloys use borax containing flux and stainless steel require , potassium fluoride containing flux. • The solder should melt before the alloy to be soldered . • The ability to flow and wet the soldered alloy ensures a strong bond between the solder and the soldered alloy.

  17. Most dental solders are gold based or silver based • Gold based solders are for cast alloys • silver solders in orthodontic applications • Gold solder- gold,Ag,Cu,Zn,and Sn,liquid at 750-900° C • Silver solder- up-to 70% Ag,Cu,Zn,and Sn,liquid at 750-900° C

  18. Heat treatment of gold alloys • Heat treatment should be done under the consideration for how the properties of alloy may change. • Gold based alloy with sufficient copper heat treatment improve the properties of alloy. • Base metal alloys heating generally deteriorates the properties of alloys. • Conventional cast gold alloys that contain sufficient copper is easily heat treated to produce a softer or harder alloy.

  19. They are softened by heating for 15 minutes at 705 °C and cooling rapidly to room temperature in water. • Heat hardening-> it takes place when alloys are heated at 370°C for 15minutes and then cooled in air. It produces increase in strength ,reduces ductility. • Dental gold castings:- Are heated either quenching or slowly cooling the casting in the mold . • For softer casting the entire mold is quenched in water. • By cooling in room temperature harder and stronger but less ductile casting is formed.

  20. The gold alloys to be used with porcelain • They harden as a result of formation of a platinum -iron compound during slow cooling from porcelain fusing temperature. • Alloys for bonding to porcelain • High gold alloys:- Noble metal of 98% ( gold, platinum and palladium). The content layer consists of iron, tin and iridium which produce hardening and form oxide layer that bonds with porcelain.

  21. Gold alloys of total metal content of 80% have largely replaced higher Karat alloys • These alloys stronger, less harder, more ductile ,less expensive and less dense. • Palladium -silver alloys:- • These form the second group of precious metal alloys for use with porcelain • Palladium 50-60%,silver30-40%,and low percentage of base metals for hardening. • The lower density of this differentiates it's from gold alloys. • The main disadvantage is the discoloration of porcelain by silver contamination.

  22. Palladium Copper Alloys:- • Alternative to palladium silver alloys • Palladium 70-80%,copper 10-15%,gallium 5-10% • The advantage of this over palladium silver alloys is that it does not produce greening affect but they tend to sag more on porcelain firing because of this it is not recommended for long span bridge work.

  23. Nickel-Chromium Alloys:­ • Non -precious alloy • Nickel 70-80%, chromium 15% (Corrosion resistance ),aluminum, beryllium and manganese. • They are stiffer than noble and precious alloys. • Nickel alloys are more difficult to cast and solder than gold or palladium-silver alloys. • Allergic reaction of nickel (more in female than in males)

  24. Cobalt chromium alloys:- • Mostly of Removable partial denture frame work • Cobalt 60%,Chromium 25%, Molybdenum and other substances. • Density is of half when compared to type IV gold alloys (lighter prosthesis) • Adequate mechanical properties and low cost. • Chromium->tarnish resistance, Cobalt­>rigidity ,Nicke1->increase ductility • Molybdenum-> strength • Beryllium-> added sometimes to reduce melting temperature. • Silicone and manganese->increase castability

  25. Cobalt chromium (Co-Cr) alloys are about 50% harder than gold alloys which makes polishing more difficult. • Casting shrinkage of Co-Cr is much more than that of gold so obtaining sufficient accuracy of crowns and bridges are difficult. • The Co-Cr nickel alloys have almost completely replaced gold alloys especially in case of partial dentures.

  26. Titanium and its alloys:- • used for dental implants and self threading pins and to retain amalgam cores and large amalgam restorations. • These alloys are resistant to corrosion has low density and modulus, high strength, and exceptional biocompatibility with biological tissues

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