Test #1-3 Flashcards
what is an amalgam
an alloy containing mercury
what is the only pure metal that is liquid at room temp
mercury
what is an alloy
a mixture of 2 or more metallic substances
how are amalgams classified
according to composition and particle size
Conventional amalgam is _____ in copper
low
What is the composition of amalgam
mercury silver tin copper zinc
What are the applications for using amalgam
load bearing restorations in posterior
pin-retained rest.
retrograde canal filling
root surface rest
What does zinc add to an amalgam
adds plasticity, makes it easier to condense
when contaminated with moisture=overenlargement of amalg
What does copper do in an amalgam
increases strength, harness, setting expansion and corrosion resistance
What is the copper content of the majority of alloys today*
high copper
What do low copper amalgams contain that is responsible for negative characteristics of low copper amaglams*
Gamma 2
What is the weakest phase of low copper amalgams
Gamma 2
What makes low copper amalgams more suseptible to corrosion
Gamma 2
What is Gamma 2
reaction wiht tin and mercury
What is the most common copper amaglam reaction
Gamma 1
What is a gamma 1 reaction
silver and mercury
the more gamma one in a high copper alloy…
the stronger the alloy is
What does Gamma 1 do
- holds original alloy particles together
- corrosion resistant
In the amalgam particles sizes what is a lathe cut
grinding of a solid metal alloy bar on a lathe, rough irregular findings of various sizes
In the amalgam particle size what is a spherical alloy
-made my spraying molten alloy into a vacuum and letting the drops fall, as they fall they become round balls
What is an admixed alloy
contains both lathe cut and spherical particles
What kind of particles are most alloys today
spherical or admixed
do to spherical particles regular shape they can
-reinforce and can be packed closer together
what are the advantages of amalgam
- easy to insert
- not techique sensitive
- resists fracture
- long service life
what are the disadvantages of amalgam
- no color match
- corrosion, tarnish
- marginal breakdown
- creep- open margins
- high thermal conductivity
what is creep
creep causes amalgam to flow and the unsupported amalgam protrudes away from margins
what happens to the unsupported edges with creep
weak and become corroded, ditch around margins
What does polishing an amalgam do
decreases corrosion
what is used to polish amalgam from course to fine
bur
pumice
tin oxide
What are the main components of ceramic- a glass material
Kaolin
Feldspar and quartz
metallic oxides
What is Kaolin
a clay found on riverbanks, becomes cohesive when wet
what is feldspar and quartz
mined from the earth and can be ground into powders, similar to sand
what are metallic oxides
ceramic pigments
What happens to feldspar when its subjected to high temperature
they fuse and form glass of the same shape
what doesnt change when feldspar is heated to high temp
silica particles
because of the feldspar and silica actions in high temps this means
a cohesive mixture that can hold its shape is formed
What is the difference between ceramic and porcelain
different amounts of feldspar, kaolin and silica
how is porcelain made
fired, which is baking at a high temp
how is ceramic made
cast or machine milled
What is fusion temperature
temp at which grains of porcelain powder fuses to form a ceramic mass
What is a glaze
creates a smooth, translucent surface similar to enamel
What are properties of ceramic/porcelain
- excellent electrical and thermal insulator
- low thermal expansion
- low tensile strength
- high compressive strength
What can porcelain be affected by
fluorine containing acids APF
What is a disadvantage of porcelain
harder than tooth structure, can cause wear of opposing teeth
What is a cad cam
computer that are used to design and cut ceramic restorations
What are veneers
a thin layer of tooth colored material cemented or bonded to the facial surface of a natural or replacement tooth to improve its appearance
What are the 2 types of veneers
direct and indirect
What are chemical/mechanical precautions for porcelain and composite
- Porcelain needs to be protected from APF
- Composite veneers are subject to scratchin
The lower the reactivity of metal the_____________*
higher its nobility
What are characteristics of noble metals
resistant to corrosion and oxidation, precious metals
WHat are characteristics of metals*
elements that conduct heat and electricity, lustrous, melleable and ductile
what are noble alloys
combines larger amts of precious metals with smaller amts of base metals to create strong, hard miextures that are highly resistant to tarnish and corrosion, expensive
What is an example of a noble metal
gold alloys
What is the gold for in gold alloys
soft, contributes to color, tarnish, and corrosion resistant, malleable and ductility
what is the copper for in gold alloys
lowers melting temp, contributes to harness and strength and corrosion resistance
What is silver for in gold alloys*
neutralizes reddish color from copper
what is platinum in gold alloys
increases strength and melting temp
What is palladium in gold alloys
less expensive than platinum, same purpose
What are examples of base metal alloys
titanium nickel/chromium nickel/cobalt molybdenum tungsten
- what base metal alloy is not sued any more because of allergy concerns
Nickel/ Nickel chromium
what is a common base alloy, used in substructure for crowns
nickel chromium
What is a karat
parts of pure gold in 24 parts
100% gold=24 karat
75% gold=18 karat
What is fineness of gold
parts of pure gold in 1000 parts of alloy
100% gold-1000 fineness
75% gold-750 fineness
What are the types of gold
type 1 and 2, 3, 4
What is type 1 gold
- soft, for simple inlays
what is type 2 gold
-medium, 2-3 surface inlays and onlays
What is type 3 gold
hard, crown and bridge
what is type 4 gold
extra hard, partial dentures
