DM 12 Metals

A metal is _______ & ______

strong & ductile

A metal provides ____________ to corrosive environment

electropositive ions

Metals can be polished to a high ________

luster

Metals can be classifed in what two groups?

Ferrous & Non ferrous

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Metals containing iron:

Ferrous

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Metals that don’t contain iron

Non ferrous

In dentistry, metals are one of the four major classes of materials used to reconstruct _______, _______, or _______ teeth.

decayed, damaged or missing

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Metals can be pictured as a lattice of positive ions surrounded by delocalized electrons, often called a

sea of electrons

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The ______ electrons are shared among neighboring atoms and are free to move throughout the solid.

valence

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Valence electrons (free/delocalized electrons) are why metals _________

conduct heat and electricity

All metals used in dentistry are health together by ________ bonds

metallic

Metallic bonds allow:

• strength

• malleability

• ductility

• thermal conductivity

• electrical conductivity

• opacity

• luster

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______(metals) ions are surrounded by a cloud of delocalized ______

positive, electrons

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Metals form cations by losing _______

electrons

Metals react with oxygen to form _________

oxides

T or F: All metals oxidize at the same rate.

False

_______ rusts over time, while ________ can remain stable for years

iron, aluminium

_______ metals such as iron, copper, zinc, and nickel take longer to oxidize.

transition

Which 3 metals do not react with the atmosphere?

palladium, platinum, gold

When metals lose an electron, it forms a positive ________

cation

T or F: metals have ability to deform under stress without breaking

True

Metals have _____ Mpa fracture toughness

25-60

Stress of being pulled apart

tensile

Stress of being pushed together

compressive

Stress of being rubbed together

shear

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How can metals conduct electricity and heat?

their free/delocalized electrons

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Metals have high density because their tightly packed ___________

crystal lattice

________ and ________ are metals used as alloying elements in dental alloys that are liquid at

room temperature.

gallium & mercury

Metals are generally resistant to chemical attack, but some require _________- to improve resistance to tarnish and corrosion

alloying elements

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________ is a material made from more than one chemical element, with at least one element being a metal.

alloy

What is the purpose of an alloy?

to enhance physical properties

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Iron + small amount of carbon =

steel

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iron + carbon + chromium

stainless steel

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gold + copper

stronger gold alloy

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chromium makes stainless steel highly __________

corrosion resistant

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A _______ metal solidifies at one fixed temperature

pure

Melting a small amount of metal & recording the temp drop at time intervals as the metal solidifies gives you what?

a cooling curve

When obtaining a cooling curve, the metal must be under what conditions?

equilibrium conditions

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Liquidus during cooling: the first crystal begins to ________

form/nucleate

Liquidus during heating: the last crystal ________ into liquid

dissolves

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Solidus during cooling: the last liquid ________

solidifies

Solidus during heating: the first liquid ________

forms

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Noble Alloys (casting metals):

gold, platinum, palladium

Base metals:

copper, nickel silver, zinc, tin, titanium

Proceain bonding alloys can be what classifications?

• High-noble alloys

• Noble alloys

• Base metal alloys

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Common removable proshtetics use what base alloys?

• chrome-cobalt alloys

• nickel-chrome alloys

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Solders do what?

join metals together & repair cast restorations

Wrought metal alloys are formed after the metal is cast. examples include:

• wire

• orthodontic wire

• brackets & bands

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__________ are metal or nonmetal dowels/rods placed within the root canal space after root canal treatment.

endodontic posts

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Endodontic posts can be classified as:

active or passive