Alloys for PFM Restorations Flashcards
____ are used for strength, but this will ultimately be opaqued so you won’t see them
connectors
Classification of PFM alloys
PFM alloys:
- noble metals - alloys that have more ____
‣ Au: •
____ = the three noble metals associated with dentistry
Au-Pd
Au-Pd-Ag = although silver isn’t used as much, because it tends to ____
‣ Pd: •
Pg-Ag,Pd-Cu,orPd-Co
◦ Base metals- alloys with \_\_\_\_ ‣ Ni-Cr-Be ‣ Ni-Cr ‣ Co-Cr = \_\_\_\_ metal frameworks ‣ Ti & Ti alloys = \_\_\_\_ work; also used for undercasting of PFM
gold
Au-Pt-Pd
corrode
nickel
partial
implant
ADA classification system
High noble
Gold content: ____
Noble metal content: ____
Noble
Gold content: ____
Noble metal content: ____
Predominantly base-metal
Gold content: ____
Noble metal content: ____
>=40 >=60 not required >= 25 not required < 25
Noble metals
Gold (Au) resistance to
____, good malleability, ____ melting point
Palladium (Pd) ____
melting point, ____ than gold, not used in pure form
Platinum (Pt) ____ melting point, does not ____ as
freely with gold, most expensive
corrosion low higher harder highest mix
Carat & Fineness • Pure gold \_\_\_\_ carat = 100% gold • Alloy 50% gold \_\_\_\_ carat • \_\_\_\_ carat jewelry 75% gold • Pure gold fineness rating \_\_\_\_ • 18 carat gold \_\_\_\_ fine
more gold = ____ the alloy will be
24 12 18 1000 750 softer
Base metals
Nickel chromium cobalt
titanium
Copper & Silver: increase the ____ of gold based alloys
Zinc: decreases ____ and increases ____
hardness
oxidation
hardness
Terminology:
- ____ (Precious) - Noble (Semiprecious) - ____
(Non precious) (Non noble)
terms precious , etc refere to ____ - NOT DENTISTRY
high-noble
base
jewelery
Grain & Crystal Structure
Similar to how ice forms.
Grains are formed by a ____; visible by ____ microscopy.
Grain boundaries are subject to ____ attack.
Alloys with ____ grains have more uniform properties.
Iridium & Ruthenium are grain ____.
Base metals have ____ grains.
Wrought alloys are drawn into wire & the grain structure has a ____ appearance.
Cast noble alloys have an ____ crystal structure which is affected by how the alloy is ____ and cooled; this is not true with ____.
crystal lattice light corrosive smaller refiners larger fibrous
ordered
heated
base alloys
CRITERIA FOR ALLOY SELECTION FOR P-FM RESTORATIONS Physical/Chemical properties - \_\_\_\_ - Noble metal content --\_\_\_\_ resistance - Hardness - ?Laboratory recommendation
- copper appears ____; high-nobles will be ____
color
corrosion
gold
yellow
Physical/chemical properties
- Modulus of elasticity (____ of the material)
• Important for occlusal forces - Yield strength
(plastic deformation, force required to ____ distort alloy) - Elongation (____)
• Noble alloys can be changed in shape - Thermal Properties
-Melting range: ____
-Thermal Creep - Density (higher, weighs more, easier to ____)
• We need to have an undercasting that can withstand the temperature that will melt the porcelain
◦ Since we have an alloy, we have a “____”
‣ Solidus - when all the alloy components are fused together as a ____
‣ Liquidus - when all the alloy components ____
◦ Creep- the porcelain oven is lower temp than will melt the ____, but we also don’t want it to change shape
stiffness permanently ductility solidus/liquidus cast melting range solid undercasting
COST
- Some labs will charge you for the ____ metal
- Highest-lowest expense: ____>noble>base
- Base metals-labs have a difficult time fitting them becauseof how ____
specific
high-noble
hard
Physical Properties
Do not memorize, just look at the trends*
• High-noble melting ranges are ____ than base-metal alloys
• Density= the more gold, the ____ the alloy
• Yield strength and ____ are linked
together: the more gold, the softer the material
lower
denser
hardness
Physical/chemical Properties
Biocompatibility
- Cytotoxicity
- Tissue irritation
• Allergies - ____
- Laboratory Workability
- ____ accuracy
- Ease of cutting/finishing
- Porcelain Compatibility
- ____
- thermal expansion
- bond strength
• Biocompatibility =anything that is ____ is considered very biocompatible (be weary of silver allergies)
• Beryllium: take caution, because when ground up the inhaled particles can cause lung cancer-so technicians
work in hoods with respirators
• Alloy and porcelain systems are designed to work together
nickel and beryllium
casting
comoposition
noble
Oxidation of PFM Alloys
Adherence Controlling Elements ____, Sn, ____
- allows fusing to occur in ____ amounts
small
Oxides on PFM Alloys
• Au-Pd-Pt
• ____ oxide
(moderate)
- Pd-Cu
- ____ oxide (high)
- Pd-Ag
- ____ (thin)
medium gray
dark brown to black
light gray
orcelain Bonding to PFM Alloys
• Oxides on metal surface bond ____ to oxides in porcelain
chemically
Greening of Porcelain
- Porcelain discolorationin crowns a & c (____)
- Nodiscoloration of crown b (____)
Pd-Ag
NiCr
Physical/Chemical properties Other Factors: - Span length, \_\_\_\_ - Metal/porcelain occlusal - \_\_\_\_
- sag resistance - you want to withstand the pressures of mastication
- can’t have alloy that is too ____ > flexing of undercasting with fracture
- flexing can occur if bridge > ____ > pressure gets placed on one of abutments
- make stiffer for ____
sag resistance cost soft loose bruxers
Physical properties
Table, ya!
ya
*Au-Pt-Pd AlloyCompositions
____ % Au, ____ % Pt, ____ % Pd, ____ % Ag ____ %basemetals(Fe,Sn,In)•
84-86 4-10 5-7 1-4 2-3
