D2 Biomaterials Lecture 3: Casting Alloys

What are the three main traits that are the most desirable properties for casting alloys?

1. Biocompatibility

2. Esthetics

3. Thermal properties

What three resistances are desirable properties for casting alloys?

1. Corrosion

2. Tarnish

3. Fracture

What is the main desirable type of material used in casting alloys?

Allergenic components

What factor should casting alloys compensate for?

Solidification

What are the elements with good metallic surfaces that retain their luster in clean dry air?

Noble metals

What is the main advantage of noble metals in casting alloys?

High resistance

What trait do noble metals indicate?

Relative inertness of element

What are the two main types of noble metals?

1. Platinum group

2. Gold

What metal is used in dental castings, but is not a noble metal?

Silver

What type of alloy is ADA Specification #5 referred to as?

Gold based alloys

What four tests must alloys pass no matter the composition?

1. Toxicity

2. Tarnish

3. Yield strength

4. Percent elongation

What is the ADA classification for an alloy that is >40% gold and >60% of noble metal elements?

High noble metal

What is the ADA classification for an alloy that contains >25% of noble metal elements?

Noble metal

What is the ADA classification for an alloy that contains

Base metal

When an alloy is identified, how are the components listed?

Largest to smallest constituent

What is the only exception to the alloy component list rule?

Elements that affect physical properties/biocompatibility

What are the three normal-fusing alloys?

1. Medium/Low gold

2. Silver-palladium

3. Silver-indium

What is the main trait of high-fusing alloys?

High fusing temperature

Which noble metal is soft and the most malleable and ductile?

Gold

What is the main resistance trait of gold?

Tarnish resistant in air and water at any temperature

What needs to match between porcelain and metal for a strong bond?

Thermal coefficient of expansion

What ratio coefficient should rise for more rigidity?

Modulus of elasticity

What is the relative fusion temperature for crown and bridge porcelains?

Medium/Low fusing

What is the relative fusion temperature for porcelains in glazes?

Ultra low fusing

Which measure is an indication of the compactness of a substance?

Density

What is the term for the stress above which the material no longer behaves totally elastically?

Proportional/Elastic limit

What is the main disadvantage of using platinum in casting alloys?

High cost

What is the main resistance trait of platinum?

High corrosion resistance

Does platinum or porcelain have a higher melting temperature?

Platinum

What is the fusion temperature of platinum?

1755°C

Is the fusion temperature higher for gold or platinum?

Platinum

Is the density higher for gold or platinum?

Platinum

Is the thermal coefficient of expansion higher for gold or platinum?

Gold

Is the modulus of elasticity higher for gold or platinum?

Platinum

Which noble metal is not used in pure state dentistry?

Palladium

What does palladium help prevent in the oral environment?

Corrosion of silver

What does palladium do if heated improperly?

Absorbs hydrogen gas

Which metal used in casting alloys is the best conductor of heat and electricity?

Silver

Does silver or gold have more hardness?

Silver

What is silver at risk for in the oral environment?

Severe tarnish

What four traits are increased with grain refining with iridium and ruthenium?

1. Tensile strength

2. Elongation

3. Resistance

4. Yield strength

Does grain refining with iridium and ruthenium affect hardness?

No

What is the internal induced force that resists the elongation of a material in a direction parallel to the direction of the stresses?

Tensile stress

What is the strength at which a small amount of permanent strain occurs?

Yield strength

What are the four wire types in current clinical practice?

1. Stainless steel

2. Cobalt-chromium

3. Beta-titanium

4. Nickel-titanium

What are Type 1 (Low) alloys used for?

Inlays

What are Type 2 (Medium) alloys used for?

Inlays/Onlays

What three procedures are Type 3 (Hard) alloys used for?

1. Inlays/Onlays

2. Pontics

3. Crowns

What four procedures are Type 4 (Extra Hard) alloys used for?

1. Crowns

2. Bridges

3. Post & core

4. Partial denture framework

What percentage of metal ceramic alloys are made of noble metals?

> 90%

What two reasons is zinc used for in metal ceramic alloys?

1. Counteract absorption of oxygen by silver

2. Increase castability

What is the reason gallium is used for in metal ceramic alloys?

Compensate for elimination of silver

At what Cu:Au ratio is the alloy heat treatable?

> 12:88

What are the two main disadvantages of heat treatment of alloys?

1. Reduce yield strength

2. Reduce elongation

What is the technique used for joining metal components in alloys?

Soldering

What is soldering used to overcome in alloys?

Distortion

What is the importance of copper in metal alloys?

Allows soldering

What is the technology used to make milled gold crowns?

CADCAM

What are the two advantages of milled gold crowns?

1. Better fit

2. Improved consistency/accuracy

What was gold replaced with in removable partial dentures?

Cobalt/Nickel - Chromium

What are the four advantages of Cobalt/Nickel - Chromium?

1. Lightweight

2. Stiff

3. Greater strength

4. Reduced cost

What trait is practically maximum strength for dental applications in casting alloys?

Yield strength

What represents the maximum strength of the casting alloy and is less influenced by variations in specimen preparation?

Tensile strength

What is the measure of the ductility of the casting alloy and it will indicate if the alloy can be burnished?

Elongation

What is the indicator of the ability of a casting alloy to resist local permanent deformation under occlusal load?

Hardness

Is the hardness of casting alloys greater or less than enamel?

Less than

What trait of chromium makes it responsible for tarnish and corrosion resistance in casting alloys?

Passivation

What are three traits are increased by carbon in casting alloys?

1. Strength

2. Hardness

3. Brittleness

What are three traits are increased by molybdenum in casting alloys?

1. Strength

2. Hardness

3. Elongation

What two traits are increased by aluminum in casting alloys?

1. Tensile strength

2. Yield strength

What trait is decreased by beryllium in casting alloys?

Fusion temperature

What trait is increased by beryllium in casting alloys?

Fluidity during casting

What technique is allowed by beryllium in casting alloys?

Electrolytic etching

What two traits are increased by manganese and silicone in casting alloys?

1. Fluidity

2. Castability

What do manganese and silicone act as in Ni containing alloys?

Boron deoxidizers

What trait is increased by iron and copper in casting alloys?

Hardness

What is the main advantage of titanium alloys?

Stable oxide layer

What are the two main disadvantages of titanium alloys?

1. High melting point

2. Chemical reactivity

What tool is needed to process titanium alloys?

Well-controlled vacuum

Do alloys with higher or lower density form complete castings more easily?

Higher