Dental Alloys Flashcards
True or False: Nobel metals form stable oxides at room temperature.
FALSE
There are ___ noble metals.
7
gold, platinum, palladium, iridium, ruthenium, rhodium, osmium
True or False: Silver is a noble metal.
FALSE, it forms black AgS in the oral environment
Precious metal classification is based upon _____.
metal price (not electrochemistry)
True or False: Relatively common metals can become precious if very high purity is acquired.
True
True or False: 22karat gold was previously used for dental restorations.
True
True or False: we now use lower-gold compositions than previously (1930s).
True
True or False: There are Types 0-6 for dental casting alloys.
False, Types 0 to 5
The current standard for dental casting alloys is ISO _____.
22674
do we need to know this!?
According to ISO Standard 22764, what are the mechanical property requirements for alloys?
- 0.2% offset yield strength minimum (Types 1-5)
- minimum percentage elongation after fracture (Types 1-5)
- minimum Young’s modulus is specified only for Type 5
____ - stress per unit amount of elastic strain (higher value = less deflection for long span frameworks)
elastic modulus
_____ - amount of stress for designated small amount of permanent strain (typically 0.1%)
yield strength
must by sufficient for PFM restorations so that there is no deformation upon functional force
_____ is the amount of permanent deformation at fracture
ductility
True or False: Ductility is less important for metal-ceramic restorations since porcelain is brittle
True
_____ - generally corresponds to strength
Hardness (wear can occur from an alloy if its Vickers hardness is greater than that of enamel ~350)
True or False: Burnishability is a characteristic considered for alloy selection
True
In classification of casting alloys, which type is very low stress bearing?
Type 0
one surface inlays, veneers
Which casting alloy type is used for RPD frameworks?
Type 4
Which casting alloy type is used for thin RPD frameworks?
Type 5
Going from Type 1 to Type 5, there is a(n) _____in yield strength and hardness.
increase
Going from Type 1 to Type 5, there is a(n) _____ in ductility.
decrease
Going from Type 1 to Type 5 casting alloys, there is a(n) ____ in ease of adjustement and burnishability.
decrease
Midas Reduced-Gold Alloy (Jelenko) Type 3/4 is composed of ____ gold.
46%
Modulay Type 2 Gold Alloy is ____ gold.
77%
Which gold alloy is used in college dental clinics?
Argenco Y+
cheap bastards… 2% gold
yellow shade from PdIn
(previously used midas ~50%)
High-Noble Metal = ___-based
Nobel Metal = ____- based
Base Metal = ____-based
high =gold
nobel = Palladium
base = nickel
True or False: High density porcelain alloys are favorable.
False, lower density preferred
True or False: Fixed Partial Dentures fabricated from Au-Pd or Au-Pd-Ag will be more resistant to masticatory forces than those fabricated from Au-Pt-Pd.
True
True or False: Palladium alloys are more technique sensitive than gold alloys. Why?
True
Palladium has a higher melting range and a greater tendency for gas incorporation in molten alloy
True or False: Price volatility of palladium has been and still is a concern.
False, it was but not anymore
Reports have been filed regarding _______ problems with Pd-Cu-Ga, but no problems arise from the alloy Freedom Plus.
bio compatibility (allergy)
What is the most important feature of conventional base metal alloys?
much lower unit cost
True or False: Conventional base metal alloys require experienced dental labs.
True, technique sensitive
Which type of alloy (base metal) is favored for metal ceramic restorations?
Ni-Cr
Which base metal alloy is used for patients with a nickel allergy?
Co-Cr
allergy =No-Cry=Co-Cr
True or False: High gold alloys are beneficial for multi-unit restorations.
False, expensive and undergo dimensional changes
True or False: Porcelain “greening” is a concern for Pd-Ag alloys.
False, problem was corrected with better furnaces and porcelain composition
Which alloy is considered the “best compromise” for cost, properties and ease of manipulation?
Gold Palladium
(Au-Pd)
(Gold and its Pal)
What is the purpose for Be in Ni-Cr alloys?
to lower fusion temperature (easier to cast) and improve bonding
What is the harm in casting with Be?
Be has an adverse effect on the lungs; fumes during casting must be properly ventilated
True or False: Patient allergies must be considered prior to alloy selection.
true
What gives Argistar Yellow LF its yellow color?
combination of Pd and Indium
What are the conventional base metal alloys used for RPD frameworks?
cobalt-chromium
nickel-chromium
cobalt-chromium-nickel
True or False: Titanium alloys have a low strength:weight ratio.
False, HIGH strength to weight
True or False: comparing gold to base metal RPD alloys, there is little difference in yield strength and ductility.
True
Which difference is most important between gold and base metal RPD alloys?
modulus of elasticity is high for base metals
(the amount of deflection allowed before breakage)
-deflection for base metal alloys is HALF that of gold
What are the advantages to using base metal alloys instead of gold for RPD frameworks?
- cost
- lower density (can make it thinner because its harder)
- high elastic modulus
- high yield strength
- corrosion resistant
Base metal alloys have excellent corrosion resistance from _______ surface films.
chromium oxide
What are the disadvantages of base metal alloys for RPD frameworks?
- limited ductility (fracture during clasp adjustment)
- wear of tooth due to VHN >350
- need for special equipment in casting
The newest technology involves _____ sintering (additive manufacturing).
laser
Which alloy is used in laser sintering?
Cobalt-Cromium
In laser sintering, a laser scans across a bed of _____ with _____ at specific sites.
powder
melting (fusing particles)
True or False: The large Phenix Dental System claims to be capable of producing 200 fixed restorations in 5 hours.
True
almost as fast as our lab
