Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
162 Cards in this Set
- Front
- Back
pure metal
|
element that ionizes positively in sln
|
|
are elemental metals used in frequently in dentistry?
|
NO
|
|
Pure metals used in dentistry
|
gold, mercury, platinum, silver, tin, copper, and zinc
|
|
properties of pure metal
|
conduct heat and electricity bc of metallic bonds (e-cloud)
|
|
when are metallic bonds formed?
|
when metal valence e- leave the nucleus and move about in the metal space lattice creating positively charged ionic cores and the e- cloud
Ex in dentistry is ZnO is metal oxide |
|
what is responsible for characteristic physcial properties of metals?
|
luster
high strength ability to undergo permanent deformation hi density opaacity thermal/electrical conductive |
|
what form are most common pure metals in?
|
alloy form
|
|
alloy
|
intimate atomic level mixture of two or more pure metals
|
|
why is alloy better than pure metal?
|
harder and stronger
|
|
difference between pure metals and alloys
|
pure metal is one element, alloy is two or more elemental metals
pure metals have one melting temp, alloys have meltin RANGE pure metals are soft and weak, alloys are hard and strong pure metals corrode easily, alloys are more resistant to corrosion |
|
pure metal
|
element that ionizes positively in sln
|
|
are elemental metals used in frequently in dentistry?
|
NO
|
|
Pure metals used in dentistry
|
gold, mercury, platinum, silver, tin, copper, and zinc
|
|
properties of pure metal
|
conduct heat and electricity bc of metallic bonds (e-cloud)
|
|
when are metallic bonds formed?
|
when metal valence e- leave the nucleus and move about in the metal space lattice creating positively charged ionic cores and the e- cloud
Ex in dentistry is ZnO is metal oxide |
|
what is responsible for characteristic physcial properties of metals?
|
luster
high strength ability to undergo permanent deformation hi density opaacity thermal/electrical conductive |
|
what form are most common pure metals in?
|
alloy form
|
|
alloy
|
intimate atomic level mixture of two or more pure metals
|
|
why is alloy better than pure metal?
|
harder and stronger
|
|
difference between pure metals and alloys
|
pure metal is one element, alloy is two or more elemental metals
pure metals have one melting temp, alloys have meltin RANGE pure metals are soft and weak, alloys are hard and strong pure metals corrode easily, alloys are more resistant to corrosion |
|
Tf
|
solidification tepmperature of a pure metal on colling and melting temp on heating
|
|
supercooling
|
cools past melting temp. occurs when crystallization begins
|
|
steps of metal solidification
|
nucleus formation
dendrite formation grain/boundary formation |
|
2 ways nucleus formation can happen
|
homogenous nucleation
heterogenous nucleation Homogenous is BEST |
|
homogenous nucleation
|
upon cooling from a completely melted alloy, solidificaition starts from a nucleus. the formation of nuclei in random process and has equal probablity of occuring at any point in the melt
|
|
what does metal solidificatin start from
|
nucleus
|
|
heterogenous nucleation
|
when foreign bodies seed the nucleus. The distribution of foreign bodies is NOT random
|
|
after nucleus formation, dendrite grwoth occurs but what does dendrite need?
|
critical radius
|
|
critical radius
|
minimus radius at which a nucleus of crystalization is formed. It is the radius when the resultant free energy decreases as radius increases
|
|
dendrite formation step of metal solidification
|
crystal dendrites form outward from the nucleus appearing like snow flakes
|
|
what demarcates each individual crystal during metal solidifcation?
|
when dendrites meet during growth and a grain boundary is formed
|
|
polycrystalline
|
when each grain is a single usit that is oriented differently that others. It consists of thousands of crystals/grains
|
|
coring
|
the difference in composition of grains from the nucleus outward
|
|
effect of grain size on alloy properties
|
small, fine grain alloys are stronger than large, course grain alloys of the same composition bc of the prescence of greater number of barriers such as grain boundaries which stop the dislocation of movement
|
|
what does hardening heat treatment (age hardening) result in?
|
increased tensile strenght and hardness, and reduced ductility of alloy
|
|
What can reverse the effects of cold working (strain hardening, lower ductility, and distortored grains)
|
heating the metal. the process is called annealing and results in eventual recrystallizaton of the metal which softens the alloy making it easier to finish and adjust the metal
|
|
how is alloy altered w/ annealing?
|
tensile strength and hardness are reduced but ductility is increased
|
|
classification of alloys
|
1. by use (inlay, crown, bridge, partial denture,etc)
2. by major element 3. by nobility (ADA classification; HN, N, PB) 4. By principle elements 5. By dominant phase system (isomorphous, eutectic, peritectic, etc) |
|
meallurgic phase
|
physically distinct, homogenous, mechanically sperable portion of a system w/ a unique crystal and structure and unique physical properties. A phase is separated from other phases by a boundary
|
|
what is equilibrium phase diagram used for?
|
so we can ID melting range
|
|
when is a complete solid sln formed?
|
when two or more pure metals are completely soluble in each other in all percentages. Examples of complete solid slns in dentistry are Ag-Pd and Au-Cu
|
|
what is limited solid solution?
|
when limited amounts of one metal dissolve in another metal. Most metals do this.
examples are Ag-Sn and Ag-Cu |
|
2 types of solid solutions
|
1. interstitial
2. substitutial depends on positio of solute atoms in the crystal space lattice |
|
factors that determine the extent of solid solubility
|
atom size
valence chem affinity crystal structure |
|
intermetallic compounds
|
chem compounds formed by solidification of two or more metals in stoichiometric ratios. cmpds like this are hard, brittle, and have unpredictable properties.
Ex in dentistry are Ag3Sn, Ag2Hg3 both are in dental amalgum, and Fe3C |
|
Eutectic alloys
|
formed by combo of metals that are miscible in liquid state but seperate in solid state. alloys at the eutectic compositon melt at one temp and comp instead of melting over a melting range. they are brittle, weak, and have low corrosion resistance.
example in dentistry is Ag-Cu found in hi copper amalgums |
|
peritectic alloys
|
due to limited solubility of two solid slns. alloys have invariant rxn at peritectic compostion and are brittle, week and have lo corrosion resistance. They are susceptible to coring
ex in dentistry are Ag-Sn in dental amalgum alloy and Pt-Ag in casting alloys |
|
coring
|
where cores have composition higher solidus temp and the surrounding matrix has compositions with lower temps
|
|
isomorphous alloy
|
contains grains of one phase, has a homogenous structure, and is solid in sln alloys
|
|
alloy
|
combination of 2 or more pure metals
|
|
amalgum
|
an alloy containing mercury
|
|
can you open mercury capsule?
|
No bc if mercury falls you have to buy special chem to clean it up
|
|
amalgamation
|
process of mixing mercury w/other metals to form amalgam
|
|
dental amalgum aka amalgam alloy
|
alloy made of silver, copper, tin, etc
|
|
how is amalgum alloy sold?
|
as loose powder, capsule, pellets, or pills
|
|
Dental amalgum aka Amalgum
|
Alloy containing mercury and dental amalgum alloy
this is final alloy |
|
3 main metals in Amalgum alloy
|
silver
copper tin |
|
Trituration
|
Forceful mixing of mercury and amalgam alloy powder
|
|
where is trituration performed?
|
in an amalgamator or triturator
this tears membrane so alloy and mercury mix |
|
who controls the amalgamator
|
operator controls the duration and amount of energy used for mexing
|
|
Amalgum alloy predominant composition
|
silver and tim
|
|
amalgam alloy with more than 0.01 %wt Zn
|
zinc containing
|
|
amalgam alloy with less than 0.01 %wt Zn
|
non zinc containing
|
|
What are zinc alloys more susceptible to?
|
moisture and delayed expansion
|
|
low copper amalgum alloys
|
called lathe cut alloys
65% wt Ag 29% wt Sn less that 6% wt Cu |
|
2 types of hi copper amalgum alloys
|
spherical alloy
admixed alloy |
|
spherical alloy
|
type of hi copper amalgum alloys
between 13-30 wt% Cu |
|
admixed alloy
|
type of hi copper amalgum alloy
between 9-20 wt% Cu |
|
what influence properties of amalgum?
|
Cu and Zn
|
|
what is a substitue for Ag in amalgam alloy?
|
4-5% Cu which results in an alloy that is harder and stronger and makes the alloy easier to comminute (mix)
|
|
what does Zn do to alloy?
|
makes alloy less brittle and acts as a deoxidizer (reducing agent)
|
|
why doe some alloy powders contain trace amounts of Hg, In or Pd?
|
to improve handling properties
|
|
ingots
|
amalgum alloy manufacturing where it is ground in a lathe or milled
|
|
molten metal
|
cast by blowing molten alloy through a nozzle to form small spheres (atomization)
this is spherical processing |
|
Admixed manufacturing process of amalgum alloy
|
lathe cut 45-60%
and spherical 30-55% |
|
homogenizing anneal of ingot
|
heat treatment to homogenize the grains; different methodes of cooling of the ingot produce different phases
|
|
partical treatment of amalgum alloy
|
treatment of ground particales w/acid results in preferential dissolution of certain particles. Particles are softened (annealed) to relieve the stresses created during grinding
|
|
particle size of amalgum alloy
|
15 micrometers to 35 micrometers.
|
|
what is different about v. small particle size of amalgum alloy?
|
less that 3 micrometers have a larger surface area per unit volume of powder and so require more Hg
smaller particle sizes result in more rapid hardening and higher early strentght less likely to get pulled out of amalgum microstructure during carving or finishing leaves behind smoother surface less likely to corrode |
|
when comaring amalgum alloy types, what alloys resist condensation better than spherical alloys?
|
lathe cut and admixed amalgum alloys resist condenstaion better than spherical alloys so spherical amagum alloys are more difficult to adapt to contoured proximal surfaces
|
|
what alloys require less Hg?
|
Spherical alloys bc they have smaller surface area per volume than lathe cut alloys
|
|
what do alloys with lo hg content have?
|
better properties
|
|
what do hi Cu amalgums have?
|
better mechanical properties
resist corrosion marginal integrity |
|
shape of lathe cut amalgum alloy
|
no consistant shape of size
|
|
shape of lathe cut amalgum alloy
|
consistant spherical shape
|
|
Describe setting rxn of dental amalgum
|
during trituration of alloy powder, mercury dissoves the surface of the alloy particles to form new phases.
on completion of trituration, the setting rxn starts and the material hardens wi first hours. Any remaining liquid mercury is completely consumed in setting rxn so no Hg residue |
|
what is Ag-Sn lathe cut lo copper particle called?
|
Gamma
|
|
When Ag-Sn lathe cut goes into sln what does Ag react with?
|
Ag goes into sln and reacts w/Hg
Ag + Hg = Ag2Hg3 called Gamma1 holds everything together |
|
When Ag-Sn lathe cut goes into solution what does Sn react with?
|
Sn goes into sln with Hg
Sn + Hg = Sn7hg called Gamma2 corrodes easily v. weak Sn combines with Cu Sn + Cu = Cu3Sn called epsilon |
|
when spherical hi Cu particle (Ag-Sn-Cu) goes into sln, what does Ag react with?
|
Ag reacts with Hg
Ag + Hg = Ag2Hg3 Gamma 1 |
|
when spherical hi Cu particle (Ag-Sn-Cu) goes into sln, what does Sn react with?
|
Sn + Hg = Sn8Hg
but v. little gamma 2 mainly reacts with the Cu Cu + Sn + Cu6Sn5 called Eta Does not corrode |
|
When doe most modern amalgams show net contraction
|
in first 24 hrs
ADA specification #1 limits 20 micrometers/cm change |
|
What does outward growth of gamma1 crystals cause?
|
expansion if sufficient amount of Hg in matrix
After rigid matrix is formed, gamma1 crystals grown into interstices containging Hg and continue this rxn |
|
What does contraction or expansio of amalgum depend on?
|
manipulation and how much it is constrained
|
|
What results in contraction of alloy?
|
hi condensation pressure
lo Hg:alloy ratios longer trituration times smaller particle size alloy |
|
Why is there a gradual expansion of Zn containing amalgam after exposure to water during trituration or condensation?
|
Caused by formation of H2 gas in restroation resulting in increased internal pressure and subsequent creep
occurs after 24 hrs but most likely after 3-5 days |
|
most common defect in amalgam
|
marginal defects. they can lead to secondary decay when plaque has accumulated at the margins
|
|
amalgums tension and compression
|
amalgum is v. brittle.
amalgum is weaker in tension (48-70 MPa) than in compression (310-510 MPa) |
|
What affect strength of dental amalgum?
|
trituration, condensation, Hg content, porosities, and hardening rate
|
|
what affect creep of dental amalgum?
|
microstructure and manipulation
|
|
Manipulation old technique
|
mercury/alloy ration
used excess Hg that was triturated with mortar and pestle, then Hg was sqeezed out in a cloth and also during cndensation resulting in variable mercury/alloy ratio |
|
what did eames tecnique used?
|
manipulation
used minimal Hg |
|
What changes mercury/alloy ratio?
|
composition
particle size shape heat treatment of alloy |
|
contemporary lathe cut mercury/alloy ratio
|
1:1
|
|
spherical mercury/alloy ratio
|
48/52
|
|
what are pros/cons of preproportional capsules with Hg/alloy ratio that are reliable?
|
convenient
eliminate Hg spill eliminate Hg exposure but are expensive and hg/alloy ratio cant be adjusted |
|
what does Hg-rich mix (too much Hg) do?
|
expands, has lower strength, increased creep and marginal breakdown
|
|
What does Hg-poor mix (too little Hg) do?
|
contracts, has lo strength, corrodes easily, rough
|
|
what happens if Hg and alloy are mixed too long (overtriturated)?
|
forces more alloy to dissolve
forms more rxn product product has smaller volume than compnonets build up heat mechanical nrg keeps crystals from growing and hitting (no expansion) material is weaker excessive contration and sets up faster |
|
What happens if Hg and alloy are not mixed long enough (undertriturated)?
|
little dissolution of alloy into Hg
Small portion of total rxn occurs crystals formed can grow and hit each other material is grainy, weak, shows hi expansion, sets slower, is rougher, and corrodes and tarnishes easily |
|
Describe setting rxn for single composition alloy (spherical)
|
It is composed of Ag-Sn-Cu
Ag goes into sln and reacts with Hg to make Gamma 1 Sn goes into sln and reacts with the Cu in the sln to make Eta which does not corrode |
|
Describe setting rxn for admixed alloy
|
Well the Ag reacts with Hg in sln to make Gamma1.
Sn reacts w/Hg to make Gamma2 but the gamma 2 reats with the Cu to make Eta only Gamma1 and Eta made (no Gamma2!) |
|
When do most modern amalgams show net contraction?
|
in first 24 hours
ADA Spec #1 limits only 20 micromol/cm change |
|
4 things that result in contraction of amalgum
|
1. hi condensation pressure
2. lo Hg:alloy ratio 3. long triuration times 4. small particle size alloys |
|
4 things that result in expansion of amalgum
|
1. lo condensation pressure
2. hi Hg:alloy ratio 3. short trituration times 4. large particle size alloys |
|
Most important whaty to avoid creep
|
Isolation
|
|
Most common defects in amalgum
|
Marginal defects bc they can lead to secondary decay
|
|
properties that effect amalgum strength
|
1. trituration
2. condensation 3. Hg content 4. porosities 5. hardening rate |
|
What properties effect amalgum creep?
|
microstructure and manipulation
|
|
Describe properties of low copper amalgum
|
hi creep
max strength at 7 days so cant polish immediately |
|
types of amalgum with lo creep
|
single and admix
|
|
Purposes of condensation
|
1. adaptation of amalgam against cavity wall
2. decrease amount of residual Hg 3. Decrease number of voids bc fewer voids improve physical properties 4. cause layers of amalgum to adhere |
|
physical properties of amalgum with more Hg
|
diminished physical properties
|
|
what happens to amalgum the longer the time elapsed between trituration and condensation
|
the weaker the amalgum
|
|
where does condenation start?
|
at the center of the restoration and stepped toward margins
|
|
why should condensatoin be performed in small increments?
|
to reduce void fromation and improve adaptation unless a large cavity is to restroed
|
|
when is Hg overfilled cavity removed?
|
during carving
|
|
what has a big effect on condensation pressure when the force is held constant?
|
the condenser
|
|
after amalgaum condenses what 3 steps occur wi the same appointment?
|
1. carving
2. burninshing 3. finishing |
|
Carving amalgum
|
reproduces tooth's missing anatomy and occlusal function. done after completion of initial set wi 5 min.
|
|
purposes of Burnishing amalgum
|
1. brings Hg to surface
2. smoothes surface 3. helps adapt margins to tooth structure to reduce microleakage |
|
Finishin amalgum
|
mechanical process by which gross irregularities are reduced and by which desired contours on restoration or tooth preparatation are developed
|
|
polishing amalgum
|
performed by using successively finer abrasives until a polished surface is achieved.
|
|
Steps for polishing amalgam
|
1. flour of pumice with rubber cup or bristle brush
2. tin oxide or Amalgloss 3. Wait 24 hours before polishing amalgam so that it adequate compressive strenght |
|
Tarnish of Amalgum
|
black Ag S. does not necessarily imply corrosion or failure
|
|
crevice corrosion
|
amalgam forms corrosion products that seal the tooth restoraiton interface over time and reduce microleakage
|
|
during surface corrosion what is formed in Cu alloys?
|
Sn oxides and chlorides are usually formed in lo and hi Cu alloys
|
|
What is formed in hi Cu alloys during surface corrosion?
|
Cu cmpds ar formed in hi cu alloys; hi cu alloys form corrsion more slowly
|
|
what can gold restoration in contact with amalgum result in?
|
galvanic corrosion and liberation of Hg
|
|
Is amalgum techinique sensitive or insensitvie?
|
technique insensitive
|
|
What is a base needed for amalgum?
|
bc amalgum conducts heat well to cememnt base is need to protect dentin and pulp
|
|
why does amalgum need to be put down in thicker sections?
|
bc it has inadequate strength in thin sections and must have minimum compressive strength of 310 MPA
|
|
What does carving amalgum too soon result in?
|
Hypomargination which results in fracture
|
|
What has better survival rates lo or hi Cu alloys?
|
hi Cu alloys have higher survival rates
|
|
What has better survival rates, with or with Zn alloys?
|
Zn containing have higher survival rates than non Zn
|
|
poorest performatnce of amalgum restoraiton
|
lo Cu non Zn amalgum
|
|
longevity of amalgum
|
12-15 years
|
|
factors controlled by dentist that determine quality of amalgum restoration
|
1. selection of alloy
2. Hg:alloy ratio 3. trituration procedure 4. condensation tecnique 5. Marginal integrity 6. Anatomical Characteristics 7. Finishing procedure |
|
factors controlled by manufactorer that determines the quality of amalgum restoration
|
1. compositon of alloy
2. heat treatment of alloy 3. manufacturing of alloy 4. surface treatment of part. 5. form of supply alloy |
|
What does UST ensure about Hg use?
|
that it has satisfactory purity wo surface contamination and has less than .02% residue (ADA Spec #6)
|
|
maximum safe environment conc of Hg vapor in air (OSHA rule)
|
0.05 mg/m3 or 50mirogram/m3
|
|
3 ways Hg gets in body
|
ingestion
inhalation skin |
|
3 formes of allergic responses to dental amalgums (Hg)
|
1. Elemental/metallic
2. inorganinc ion 3. Organic ion |
|
elemental/metallic Hg allergic response
|
absorbed via skin or by inhalation as a vapor
|
|
inorganic ion Hg allergic response
|
absorbed poorly in gut
|
|
organic (methyl or ethyl Hg) allergic response
|
methyl mercury produced from Hg by bacteria is most toxic form and v. effieiently absorbed in gut (comes from seafood)
|
|
half life of Hg in body
|
long 20-90 days
|
|
mulling
|
squeezing freshly mixed mass of amalgum to express Hg from masss
DONT DO |
|
Why should hi spped evacuation and rubber dam be used during removal of old fillings?
|
bc more Hg is released during removal of amalgum
|
|
how long has amalgum been used?
|
170 years with less than 100 cases of allergic rxns in 60 years
|
|
why are countries banning amalgum
|
environmental concerns
|
|
amt of Hg in food, air, and water vs Hg in amalgum
|
food= 15 micrograms
air= 1 microgram water= 0.4 microgram amalgum= 1.7 microgram |