Metals in dentistryMetals in dentistry

Libyan International Medical UniversityLibyan International Medical University

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Dental amalgamDental amalgam Casting alloysCasting alloys Wrought metal wireWrought metal wire Metals used in orthodonticMetals used in orthodontic Implant materialsImplant materials Endodontics postsEndodontics posts

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• Pure gold is the noblest of all dental metals.Pure gold is the noblest of all dental metals.• It is inactive chemically, is not affected by air, It is inactive chemically, is not affected by air,

heat, moisture and most solvents. heat, moisture and most solvents. • It resist tarnish and corrosion.It resist tarnish and corrosion.• Its thermal expansion co-efficient is similar to that Its thermal expansion co-efficient is similar to that

of tooth.of tooth.• It is malleable (ability of a material to rolled into It is malleable (ability of a material to rolled into

sheet with out fracture).sheet with out fracture).• It is ductile (ability of material to be stretched with It is ductile (ability of material to be stretched with

out rupturing).out rupturing).• Because of these properties, it’s the most ideal Because of these properties, it’s the most ideal

restorative material for preserving tooth structure restorative material for preserving tooth structure in non- esthetic areas.in non- esthetic areas.

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• Metals can be divided into two groups Metals can be divided into two groups

• Noble metalsNoble metals :-that are used in dental :-that are used in dental casting alloys are gold(Au), palladium(Pd) casting alloys are gold(Au), palladium(Pd) and platinum(Pt) and platinum(Pt)

• In dentistry silver is not considered as noble In dentistry silver is not considered as noble metal. metal.

• • Base Metals:-Base Metals:-InIn dental casting alloys,these dental casting alloys,these metal includes titanium(Ti), nickel(Ni), metal includes titanium(Ti), nickel(Ni), silver(Ag), zinc (Zn) and others. silver(Ag), zinc (Zn) and others.

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Metal is elements that ionizes positively in Metal is elements that ionizes positively in solutionsolution

Metal have certain typical properties, such as:Metal have certain typical properties, such as:

1. Luster1. Luster

2. opacity2. opacity

3. density3. density

4. strength4. strength

5. thermal and electrical conductivity5. thermal and electrical conductivity

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• Currently available direct gold can be divided Currently available direct gold can be divided

into three categories:- into three categories:-

1. Foil (fibrous gold) 1. Foil (fibrous gold)

2. Electrolytic precipitate (crystalline gold) 2. Electrolytic precipitate (crystalline gold)

3. Powdered gold 3. Powdered gold

Gold Foil Gold Foil • Gold foil is the oldest of all products .It has been Gold foil is the oldest of all products .It has been

used for thousands of years. It was probably the used for thousands of years. It was probably the first form used as a dental restorative material first form used as a dental restorative material

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

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• Annealing:- It is a process of heating gold Annealing:- It is a process of heating gold foil to remove surface impurities to make it foil to remove surface impurities to make it cohensive. cohensive.

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

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• The amount of gold in an alloy can be The amount of gold in an alloy can be described in several ways besides described in several ways besides percentage percentage

• KaratKarat is used to measure gold content in . is used to measure gold content in . jewelry. jewelry.

• Fineness,Fineness, Fineness can be obtained by Fineness can be obtained by multiplying the percentage of gold by 10. multiplying the percentage of gold by 10.

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Gold Alloys for CastingGold Alloys for CastingCasting:Casting:• It is a process by which a wax pattern of a dental It is a process by which a wax pattern of a dental

restoration is ultimately converted into an exact replicate restoration is ultimately converted into an exact replicate in metal. in metal.

• Gold alloys are classified in dentistry as Gold alloys are classified in dentistry as • Type 1:- Soft (for restorations subject to very slight stress Type 1:- Soft (for restorations subject to very slight stress

such as inlays) such as inlays) • Type II:- Medium ( for restoration subject to moderate Type II:- Medium ( for restoration subject to moderate

stresses such as onlay) stresses such as onlay) • Type III:- Hard ( for high stress situation such as Type III:- Hard ( for high stress situation such as

onlays ,crowns, thick veneer crowns and short span fixed onlays ,crowns, thick veneer crowns and short span fixed partial denture.) partial denture.)

• Type IV:- Extra hard (For extremely high stress states, Type IV:- Extra hard (For extremely high stress states, such as endodontic post and cores, thin veneer crowns, such as endodontic post and cores, thin veneer crowns, long span fixed partial dentures, and removable partial long span fixed partial dentures, and removable partial dentures. dentures.

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• Low carat gold alloys Low carat gold alloys is light golden colour is light golden colour

and has gold 40%, Palladium is not higher than and has gold 40%, Palladium is not higher than 6%, Copper and silver 54%. Palladium has tarnish 6%, Copper and silver 54%. Palladium has tarnish resistance. resistance.

• White gold alloys White gold alloys : - Lower percentage of gold : - Lower percentage of gold about 30%, greater amount of palladium 10-35%, about 30%, greater amount of palladium 10-35%, silver 35-60% & copper 6-25% silver 35-60% & copper 6-25%

• Palladium Palladium acts as potent whitener, it absorbs acts as potent whitener, it absorbs hydrogen and other gases during melting and hydrogen and other gases during melting and produce porous casting produce porous casting

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Ingredients of gold alloyIngredients of gold alloy

• Gold:- Gold:- (60-71 %) Colour, tarnish resistance and (60-71 %) Colour, tarnish resistance and ductility ductility

• Copper:-( Copper:-( 11-16%) reddish appearance, improve 11-16%) reddish appearance, improve hardness and strength, lower fusion temperature , hardness and strength, lower fusion temperature , lower tarnish resistance as well. lower tarnish resistance as well.

• Silver:-(4.5-20%) hardness, strength, lower tarnish Silver:-(4.5-20%) hardness, strength, lower tarnish resistance resistance

• Platinum:-(0-3.5%) strength, raise fusion point Platinum:-(0-3.5%) strength, raise fusion point

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• Palladium:- Whitens the alloy. Alloys more than Palladium:- Whitens the alloy. Alloys more than 6% palladium take on a whiter colour. 6% palladium take on a whiter colour.

• Zinc (0.5% ):- Deoxidizing element, it reduces the Zinc (0.5% ):- Deoxidizing element, it reduces the oxygen content (Oxygen released in solidification oxygen content (Oxygen released in solidification results in porosity) results in porosity)

• Iridium:- Grain refiner (grains are tiny crystals of Iridium:- Grain refiner (grains are tiny crystals of a metal seen under the microscope ). Porosity is a metal seen under the microscope ). Porosity is usually seen with in and along the grain usually seen with in and along the grain boundaries boundaries

• Fine grain alloysFine grain alloys; stronger and more ductile ; stronger and more ductile • Coarse grained alloysCoarse grained alloys; large grains ; large grains

Iron,Tin,Indium:- Used with porcelain .Acts as Iron,Tin,Indium:- Used with porcelain .Acts as hardening and bonding agents. hardening and bonding agents.

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Biocompatibility of alloys Biocompatibility of alloys

• Pure metals (gold and palladium ) are less Pure metals (gold and palladium ) are less toxic followed by silver, nickel and copper toxic followed by silver, nickel and copper

• Lower gold + high copper alloy- Increase Lower gold + high copper alloy- Increase cell toxicity and greater tarnish. (Palladium cell toxicity and greater tarnish. (Palladium additions reduces copper toxicity) additions reduces copper toxicity)

• Nickel-allergen alloys Nickel-allergen alloys

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Soldering and Brazing Soldering and Brazing

• Soldering:Soldering:

Is joining metals at low temperature (below 450°C) Is joining metals at low temperature (below 450°C) • Brazing:Brazing:

Is joining metals at high temperatures (above 450°C) Is joining metals at high temperatures (above 450°C)

SoldersSolders• In dentistry solders are special alloys used to join In dentistry solders are special alloys used to join

metals. Soldering involves the use of flux, which metals. Soldering involves the use of flux, which is a material that cleans the alloy to be soldered is a material that cleans the alloy to be soldered and dissolves any surface oxides on the metal. and dissolves any surface oxides on the metal.

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• For an alloy to be soldered all it's oxides must be For an alloy to be soldered all it's oxides must be eliminated to allow wetting and flowing of the eliminated to allow wetting and flowing of the solder on the alloy surface. solder on the alloy surface.

• Fluxes comes in pastes, liquids and powders.Fluxes comes in pastes, liquids and powders.• Gold based alloys use borax containing flux and Gold based alloys use borax containing flux and

stainless steel require , potassium fluoride stainless steel require , potassium fluoride containing flux. containing flux.

• The solder should melt before the alloy to be The solder should melt before the alloy to be soldered . soldered .

• The ability to flow and wet the soldered alloy The ability to flow and wet the soldered alloy ensures a strong bond between the solder and the ensures a strong bond between the solder and the soldered alloy. soldered alloy.

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• Most dental solders are gold based or silver Most dental solders are gold based or silver based based

• Gold based solders are for cast alloys Gold based solders are for cast alloys • silver solders in orthodontic applications silver solders in orthodontic applications • Gold solder- gold,Ag,Cu,Zn,and Sn,liquid Gold solder- gold,Ag,Cu,Zn,and Sn,liquid

at 750-900° C at 750-900° C • Silver solder- up-to 70% Ag,Cu,Zn,and Silver solder- up-to 70% Ag,Cu,Zn,and

Sn,liquid at 750-900° C Sn,liquid at 750-900° C

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Heat treatment of gold alloysHeat treatment of gold alloys

• Heat treatment should be done under the Heat treatment should be done under the consideration for how the properties of alloy may consideration for how the properties of alloy may change. change.

• Gold based alloy with sufficient copper heat Gold based alloy with sufficient copper heat treatment improve the properties of alloy. treatment improve the properties of alloy.

• Base metal alloys heating generally deteriorates Base metal alloys heating generally deteriorates the properties of alloys. the properties of alloys.

• Conventional castConventional cast gold alloys that contain gold alloys that contain sufficient copper is easily heat treated to produce a sufficient copper is easily heat treated to produce a softer or harder alloy. softer or harder alloy.

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• They are softened by heating for 15 minutes at They are softened by heating for 15 minutes at 705 °C and cooling rapidly to room temperature in 705 °C and cooling rapidly to room temperature in water. water.

• Heat hardening-> it takes place when alloys are Heat hardening-> it takes place when alloys are heated at 370°C for 15minutes and then cooled in heated at 370°C for 15minutes and then cooled in air. It produces increase in strength ,reduces air. It produces increase in strength ,reduces ductility. ductility.

• Dental gold Dental gold castings:- Are heated either castings:- Are heated either quenching or slowly cooling the casting in the quenching or slowly cooling the casting in the mold . mold .

• For softer casting the entire mold is quenched in For softer casting the entire mold is quenched in water. water.

• By cooling in room temperature harder and By cooling in room temperature harder and stronger but less ductile casting is formed. stronger but less ductile casting is formed.

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• The gold alloys to be used with porcelain The gold alloys to be used with porcelain

• They harden as a result of formation of a They harden as a result of formation of a platinum -iron compound during slow platinum -iron compound during slow cooling from porcelain fusing temperature. cooling from porcelain fusing temperature.

• Alloys for bonding to porcelain Alloys for bonding to porcelain

• High gold alloys:- High gold alloys:- Noble metal of 98% Noble metal of 98% ( gold, platinum and palladium). The ( gold, platinum and palladium). The content layer consists of iron, tin and content layer consists of iron, tin and iridium which produce hardening and form iridium which produce hardening and form oxide layer that bonds with porcelain. oxide layer that bonds with porcelain.

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• Gold alloys of total metal content of 80Gold alloys of total metal content of 80%% have have largely replaced higher Karat alloys largely replaced higher Karat alloys

• These alloys stronger, less harder, more These alloys stronger, less harder, more ductile ,less expensive and less dense. ductile ,less expensive and less dense.

• Palladium Palladium -silver alloys:- -silver alloys:- • These form the second group of precious metal These form the second group of precious metal

alloys for use with porcelain alloys for use with porcelain • Palladium 50-60%,silver30-40%,and low Palladium 50-60%,silver30-40%,and low

percentage of base metals for hardening. percentage of base metals for hardening. • The lower density of this differentiates it's from The lower density of this differentiates it's from

gold alloys. gold alloys. • The main disadvantage is the discoloration of The main disadvantage is the discoloration of

porcelain by silver contamination. porcelain by silver contamination.

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• Palladium Copper Alloys:-Palladium Copper Alloys:-

• Alternative to palladium silver alloys Alternative to palladium silver alloys

• Palladium 70-80%,copper 10-15%,gallium Palladium 70-80%,copper 10-15%,gallium 5-10% 5-10%

• The advantage of this over palladium silver The advantage of this over palladium silver alloys is that it does not produce greening alloys is that it does not produce greening affect but they tend to sag more on affect but they tend to sag more on porcelain firing because of this it is not porcelain firing because of this it is not recommended for long span bridge work. recommended for long span bridge work.

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Nickel-Chromium Alloys: Nickel-Chromium Alloys:

• • Non -precious alloy Non -precious alloy • Nickel 70-80%, chromium 15% (Corrosion Nickel 70-80%, chromium 15% (Corrosion

resistance ),aluminum, beryllium and manganese. resistance ),aluminum, beryllium and manganese.

• • They are stiffer than noble and precious alloys. They are stiffer than noble and precious alloys. • Nickel alloys are more difficult to cast and solder Nickel alloys are more difficult to cast and solder

than gold or palladium-silver alloys. than gold or palladium-silver alloys. • Allergic reaction of nickel (more in female than in Allergic reaction of nickel (more in female than in

males) males)

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Cobalt chromium alloys:-Cobalt chromium alloys:- • Mostly of Removable partial denture frame work Mostly of Removable partial denture frame work • Cobalt 60%,Chromium 25%, Molybdenum and Cobalt 60%,Chromium 25%, Molybdenum and

other substances. other substances. • Density is of half when compared to type IV gold Density is of half when compared to type IV gold

alloys (lighter prosthesis) alloys (lighter prosthesis) • Adequate mechanical properties and low cost. Adequate mechanical properties and low cost. • Chromium->tarnish resistance, Cobalt Chromium->tarnish resistance, Cobalt

>rigidity ,Nicke1->increase ductility >rigidity ,Nicke1->increase ductility • Molybdenum-> strength Molybdenum-> strength • Beryllium-> added sometimes to reduce melting Beryllium-> added sometimes to reduce melting

temperature. temperature. • Silicone and manganese->increase castability Silicone and manganese->increase castability

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• Cobalt chromium (Co-Cr) alloys are about Cobalt chromium (Co-Cr) alloys are about 50% harder than gold alloys which makes 50% harder than gold alloys which makes polishing more difficult. polishing more difficult.

• Casting shrinkage of Co-Cr is much more Casting shrinkage of Co-Cr is much more than that of gold so obtaining sufficient than that of gold so obtaining sufficient accuracy of crowns and bridges are accuracy of crowns and bridges are difficult. difficult.

• The Co-Cr nickel alloys have almost The Co-Cr nickel alloys have almost completely replaced gold alloys especially completely replaced gold alloys especially in case of partial dentures. in case of partial dentures.

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Titanium and its alloys:- Titanium and its alloys:- • used for dental implants and self threading used for dental implants and self threading

pins and to retain amalgam cores and large pins and to retain amalgam cores and large amalgam restorations. amalgam restorations.

• These alloys are resistant to corrosion has These alloys are resistant to corrosion has low density and modulus, high strength, and low density and modulus, high strength, and exceptional biocompatibility with biological exceptional biocompatibility with biological tissues tissues