ALLOYS

ALLOYS

are mixtures of metallic or nonmetallic elements

ALLOYS

have better properties for dental restorations than any single element

ALLOYS

have a crystal structure

CRYSTALS

under a microscope, makikita to and grains ng alloys

CRYSTALS

are formed when molten alloys freezes

Grain boundaries

- lines between the crystals

GRAINS

- it’s size is important to the properties of the alloy

smaller grain

=more desirable

Grain refiners

elements that are added to gold based alloys to reduce grain size

CASTING

a wax model of a restoration is made, and alloy is melted and cast into the shape of the wax

Dental casting alloys

refers to the alloy sa casting

CERAMIC BONDING ALLOYS OR CERAMIC FUSED TO METAL ALLOYS

for anterior or posterior restorations where ceramic can be bonded over the alloy to provide an esthetic result

Ceramic metal restorations

have been called “porcelain fused to metal restorations or PFMs

Ceramic metal restorations

the restoration has an inner layer of metal called a substructure

substructure

to which PFM and ceramic are bonded

Metal

must be thick enough to have strength and rigidity

Ceramic

must be thick enough so esthetic demands are met

Oxide layer

where the chemical bonding takes place

Oxide layer

its composition and thickness are crucial to successful long term bonding of ceramic

For many base metal alloys

an oxide layer forms naturally and may even be too thick

High noble and some noble alloys

do not naturally form a efficient oxide layer

Oxides

mediates a chemical bind with the ceramic

Thermal expansion

is critical to the application of ceramic to the alloy

expand

Alloys and ceramics ___ when heated

contract

Alloys and ceramics ___ when cooled

color of the oxide

must be masked completely by porcelain or the restoration will not appear natural

Greening

a slight tinge brought about by ceramic contaminations

WROUGHT ALLOYS

alloys that are first cast then shaped by mechanical force into their final force

WROUGHT ALLOYS

are used for orthodontic wires, endodontic files, or temporary crowns

WROUGHT ALLOYS

have a grain structure often referred as fibrous

Fibrous structure

responsible for increased yield strength and hardness compared with the cast from of the alloys

SOLDERS

must be melted without distorting the alloy they join

High noble metal alloys (HM)

contains >40 wt% Au and >60 wt% noble metals

Noble metal alloys (N)

contains >25 wt% of noble metals

Predominantly base metal alloys (PB)

contains <25 wt% of noble metals

Base metal-

this classification is popular among manufacturers

PURE GOLD

easy to melt, purify, and manipulate

Gold foil

the first dental restorative material

PURE METAL

lack appropriate properties for dental restorations so metals and nonmetals are mixed together to form alloys

NOBILITY OF AN ALLOY

is usually expressed as the sum percentage of the noble metals

NOBLE METALS

are resistant to corrosion even under extreme conditions

NOBLE METALS

good in oral cavity

Precious metals

are expensive and rare but “precious” should non be used because it indicates cost

Silver

a noble metal that easily corrodes in the oral environment

NOT NOBLE METALS

are not bad metals

NOT NOBLE METALS

used for strength, flexibility, and wear properties that are necessary for dental restoration

NOT NOBLE METALS

have greater percentage of base metals

Base metals

are used in dental casting alloys

Base metals

includes titanium (T), nickel (Ni), copper (Cu), silver (Ag), zinc (Zn)

Base metals

in pure form, may greater tendency siya to corrode than noble alloys pero except sa titanium

Titanium

is nearly pure for endosseous implants

GOLD

is used because of its excellent resistance to corrosion, good malleability, yellow and relatively low melting point

GOLD

has low melting point for casting (1064 degrees celsius)

Carat

is used to describe the gold content of jewelry

Gold content

may be expressed in terms of fineness by multiplying the percentage of gold by 0

PALLADIUM

second common component of dental casting alloys

PALLADIUM

whitens the color of the gold based alloys

PALLADIUM

has excellent corrosion resistance but it has higher melting point (1554 degrees celsius)

PALLADIUM

much harder than gold

PALLADIUM

s often mixed with gold based alloys to increase their hardness or increase the liquids

PLATINUM

PLATINUM

third most common noble element

PLATINUM

have high melting point (1772 degrees celsius)

PLATINUM

is harder than palladium

PLATINUM

is used less because it does not mix freely with gold

PLATINUM

most expensive among the three metals

COPPER

has reddish color

COPPER

hardens gold or palladium based metals

SILVER

- is also used to harden gold based alloys

ZINC

has been used as a hardener for gold platinum alloys

ZINC

has low melting point (420 degrees celsius) that prevents oxidation during casting process

COLOR

yellow or silver hues

COLOR

may contain gold or not

COLOR

is not a good predictor of the alloy’s components, composition, physical properties, or biocompatibility

MELTING RANGE

must be higher than the fusion temperature of the ceramic

950 to 1000 degrees C

the alloy is heated gradually from room temperature

950 degrees C

the first sign of liquid formation

975 degrees C

some of the alloy will be liquid, but some will still be solid

1000 degrees C

all of the alloy will be liquid

Liquidus

the temperature at which all of the alloy melts on heating

Liquidus

determines the burnout temperatures and which investments are necessary for casting

Solidus

the temperature at which all of the alloy freezes on cooling

Solidus

is important to soldering because if soldering operation heats the alloy above its solidus, then the alloy loses its shape and the soldering procedure will be a failure

Higher density alloys

are generally more easier to cast

Higher density alloys

cost more because more mass is present in any given volume of restoration

Gravity

can accelerate the molten metal more easily into the casting mold

MODULUS STRENGTH

characterizes its stiffness or resistance to bending

Cast restorations

must be stiff to resist the forces of occlusion

Orthodontic wires or partial denture alloys

require a low modulus (flexibility) to allow flexure for the allot to perform approximately

STRENGTH

ability of the alloy to resist permanent change in strength

Yield strength

the most common strength value used to compare the strength of alloys

Offset

an indication of the amount of distortion

HARDNESS

an indication of how easy the alloy is to polish or indent

HARDNESS

- is measured by indenting to alloy with a diamond tip under a certain weight

HARDNESS

units are expressed as kg of mass required to form an mm2 indention, or kg/mm2

HIGH NOBLE ALLOYS

must have a nole metal content of at least 60% by weight and a gold content of at least 40%

HIGH NOBLE ALLOYS

are the most expensive

Predominantly base metal alloys

have a noble metal content of less than 25%

Predominantly base metal alloys

most commonly contain primarily nickel, cobalt, or titanium

Predominantly base metal alloys

have extremely high yield strengths and hardness but relatively low densities