Dental Materials Test II

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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: combination of 2 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: where cores have composition higher solidus temp and the surrounding matrix has compositions with lower temps
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
isomorphous alloy: contains grains of one phase, has a homogenous structure, and is solid in sln alloys
amalgum: an alloy containing mercury
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: 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

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