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What are the four classes of materials used in dentistry?
Metals, ceramics, polymers and composites
Metals and Metal alloys
Desirable properties of dental Casting allows
Bonds formed between all the metals are called
Metallic Bonds
How are metallic bonds formed?
Formed from the attraction between metal atoms and surrounding sea of delocalized atoms, valence electrons can move freely over entire metal
What are the metals called that has iron as a main constituent?
Ferrous Metals
What are the examples of ferrous metals?
steel, stainless steel, cast iron and titanium
What are the metals called that does not have iron as a main constituent?
Non-ferrous metals
What are the examples of non-ferrous metals?
Aluminium, copper, zinc, nickel, titanium
A solid material that is typically hard, shiny, malleable, fusible and ductile with good electrical and thermal conductivity is called
Metal
What are metal alloys?
Alloys are man made materials. A metallic substance composed of tow and more elements.
What are some physical properties of Metals?
- Good electrical and thermal properties
- Malleable
- High density
- Ductile
- Posses metallic luster
- Solid at room temp
Ability to be hammered into sheets is called
Malleable
Ability to be drawn into wires is called
Ductile
How does atoms arrange themselves after the molten metal solidifies?
Crystal structure
What are the three types crystal structures?
1. Simple cubic
2. Face centered cubic
3. Body centered cubic
- face and body centered are most common
Cubic crystal system
Which metals form a face centered crystal structure?
Aluminum, copper, nickel, gold/silver, platinum/palladium
Which metals form a body centered crystal structure?
Iron, Tungsten, Chromium, Titanium
What are the four stages during the solidifications in metals?
1. Nucleation
2. Crystal growth
3. Grain formation
4. Polycrystalline structure
Which stage in solidification of metal begins by the appearance in the molten metal of tiny regions called nuclei which grow to solid crystals by further depositions of atoms
Nucleation
Nucleation
During the solidification of metals, what remains constant?
Temperature
Cooling Curve of Metal
The solidification of alloys have the same process as metals but the alloys crystal have what structure?
Dendritic
During the solidification of alloys, when does the temperature change occur?
During them transition from liquid to solid
Cooling curve of alloy
What crustal structure turn does metal have during solidification?
Equiaxed grain structure
All metals and alloys used as restorative materials in dentistry are
Crystalline solids
TRUE Or FALSE
Some metals require allowing elements to resist tarnish and corrosion in the oral environment
True
Which metal is required in alloys based on iron, nickel, or cobalt to provide passivation of the alloy through the formation of a thin surface layer of chromium oxide?
Chromium
Which metals do not require alloying elements ?
Nobel metals (e.g. gold, palladium and platinum)
Which metal alloys are easy to manipulate, have very low corrosion properties in the mouth, and are the most expensive allows?
High Nobel metal alloys
Which metal alloys have low corrosion properties in the mouth, are expensive and its strength and hardness are as equal or greater than high Nobel metal alloys?
Nobel Metal alloys
Which metal alloys have extremely high strength, difficult to manipulate, high corrosion and have low cost?
Base metal alloys
Which metal alloys have ≥ 40% Au?
High Nobel
Which metal alloys have ≥ 25% Au?
Noble
Which metal alloys have < 25% Au?
Base metal
What are the common casting alloys used in dentistry ?
Cobalt, gold, iron, nickel, palladium, silver and titanium
High noble and noble alloys
How are alloys classified by composition?
Type I
Type II
Type III
Type IV
Which type of alloys have low strength, used for casting subjected to a very slight stress such as inlays ?
Type I
Which type of alloys have medium strength, used for casting subjected to moderate stress such as inlays, inlays and full crowns?
Type II
Which type of alloys have high strength, used for casting subjected to high stress such as onlays, thin copings, pontics, crowns and saddles?
Type III
Which type of alloys have extra-high strength, used for casting subjected to very high stress such as saddles, bars, clasps, single units, and partial denture framework?
Type IV
Traditionally, gold content of dental casting alloys have been referred to in terms of
Karat and Fineness
How does the karat system specify the gold content of an alloy?
Based ob parts of gold per 24 parts of the alloy
Unit that describes the gold content in noble metal alloys by the number of parts of gold per 1000 parts of alloys is called
Fineness
Carbon + Iron
Steel
Chromium + Iron
Stainless Steel, it is highly resistant to corrosion
Copper + gold
Increases strength and resistance to permanent deformation
What is a softening heat treatment?
It is a process to make a material as soft as possible.
What temperature is used in softening heat treatment, and how does it affect the material?
700 degrees for 10 mins
it decreases strength, increases ductility and decreases brittleness and internal stress
What is a hardening heat treatment?
It is a process to make a material as hard as possible.
What temperature is used in hardening heat treatment and how does it affect the material?
heated to 450 degree and gradually cooled to 250 degree for 25-35 mins.
it increases strength, reduces ductility, increases brittleness, reduces corrosion resistance and increases internal stress
Annealing can take place in which three stages?
1. Recovery
2. Recrystalization
3. Grain growth
What should gold alloy contain to be treated with heat?
needs >8% of Cu
Only which type of gold alloys can be treated with heat due to its high Cu content?
Class III (78% Au & 10% Cu)
Cass IV (75% Au & 12% Cu)
What are the three stages of shrinkage during casting?
What are the examples of Noble metals ?
Gold, platinum, palladium, iridium, ruthenium and rhodium
What are characteristics of gold?
soft, malleable, ductile, yellow in color
Which metals do gold alloyed with to develop hardness, durability, and elasticity?
Copper, silver, platinum
Which metal is blues-white in color, is tough, ductile, malleable and has hardness similar to copper?
Platinum
Platinum __________ the hardness and elastic qualities of _____________
increases, gold
Which metal has density a little more than half that of platinum and is combined with other metals?
Palladium
Which metals are used in small amounts as grain refiners to keep the grain size small which improves the mechanical properties?
Indium and Ruthenium
Which metal has a high melting point and us used with platinum to form fire thermocouples used in furnaces
Rhodium
What are base metals combined with to develop alloys suitable for dental restoration?
Noble metals
What are examples of base metals?
Silver, copper, zinc, indium, tin and nickel
Which metal is malleable, ductile, white metal, which is stronger and harder than gold but softer than copper?
Silver
Why is pure silver not used in dental restorations?
Because black sulfide that forms on the metal in the mouth
What can be added to silver alloys to prevent rapid corrosion?
Palladium
Which metal is malleable, ductile with high thermal and electrical conductivity?
Copper
Which alloy uses copper to reduce the melting point and strengthen the alloy?
Palladium-bases alloy
What does adding 10% by weight of copper to gold increase?
tensile strength from 105 MPa to 395 MPa
hardness from 28 to 85
Which metal has a tendency to tarnish in moist air and is soft, brittle, and low strength in its pure form and is low in density?
Zinc
What does zinc act as. when the alloy is melted?
scavenger of oxygen
What happens if too much is zinc is present?
It will increase the brittleness of the alloy as it is a deoxidizing agent.
Which metal is soft, gray-shite with low melting point, is not tarnished by air or water and is used as a replacement for zinc in some gold-based alloys?
Indium
True or False
Indium is a common component of some noble ceramic dental alloys?
True
Which metal is not subject to tarnish in air and are ingredients in golf-based dental solders?
Tin
What does Tin combines with to produce a hardening effect but also increase Brittleness?
Platinum and palladium
Which meta is used in small quantities in gold-based allows, and whitens the alloy and increases its strength and hardness?
Nickel
Which metal has the highest melting temperature if all the metals used for metal-ceramic prostheses are resistant to sag deformation?
Titanium
There are five unalloyed grades (grades 1-4 and 7) of commercially pure titanium based on concentration of
oxygen and iron
Silver-Palladium alloy contains predominantly
silver but has to have at least 25% palladium
The addition of palladium in silver-palladium alloy promotes
tarnish resistance
Cu free Ag-Pd alloys with 72% Ag and 25% Pd have properties of
Type III gold alloys
Addition of CU to Ag-Pd alloy will have properties of
Type IV gold alloys
The most common Au-Ag-Pd alloys have
39%-53% Au and 25%-35% Pd
What are the characteristics of Au-Pd-Ag alloys?
High melting range
better resistance to sag deformation at higher temps.
Au-Pd alloy was introduced to overcome the
porcelain discoloration
Which alloy has a lower thermal contraction coefficient than that of Au-Pd-Ag or Pd-Ag alloys?
Au-Pd alloys
Au-Pd alloy
Which alloy is not used much in the dental field, does not contribute to porcelain discoloration and has physical properties similar to Au-Pd alloys?
Pd-Au alloys
Which alloy has potential for porcelain discoloration, increase in silver content increases thermal contraction coefficient?
Pd-Au-Ag alloys
Which alloy is gold free and is used for metal-ceramic restorations?
Pd-Ag alloys
Pd-Ag alloy
What causes the discoloration of porcelain and what color is the discoloration?
It is caused by the solver content in the metal
its green
The ability of a mate and its veneering porcelain to contract at similar rates is called
Thermal compatibility
