Dental Materials Science Exam 2 Materials

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an element that ionizes positively in solution is called a: Pure Metal

examples in dentsitry are
gold, mercury, platinum, silver, tin, copper, zinc
the presence of metallic bonds allows metals to readily what with heat and electricity: conduct them
whats another name for metallic bonds: electron "cloud" or "gas"
How do metallic bonds form: when metal valence electrons leave the nucleus and move about in the space lattice, this creates positively charged ionic cores and a negatively charged "cloud"
What are the characteristic properties of metals: ability to conduct thermal energy and electricity, luster, high density and strenght, opacity, ability to undergo significant permanent deformation
an intimate atomic level mixture of 2 or more pure metals is called a what: Alloy

NOTE alloys are usually stronger than their individual components
What are the differences between pure metals and alloys: pure metals are weak and soft while alloys are hard and strong
pure metals are eaisly corroded while alloys are less easily corroded especially after Cr treatment
Pure metals are 1 element metals, while alloys are 2 element metals
Pure metals have a melting point while alloys have a melting range
What is the melting range of ADA Class III gold: 932-960 deg C
know the table and slide info for Solidification of Metals slide on 2nd page of Metals/Alloys handout: know slide
Nucleus formation that results from a random process that has equal probability of occuring anywhere in the melt is called: homogenous nucleation
When foreign bodies such as container walls or dust "seed" the nucleus and the formation of nuclei are not random its called what: Heterogeous Nucleation
The radius at which a nucleus of crystallization is formed is called: Critical Radius

defined- is the radius when the resultant free energy decrease as radius increases
How do crystal dendrites form: they form outward from the nucleus, appearing like snowflakes
When dendrites meet during growth, they form what: grain boundary

this demarcates each individual crystal(called a grain)
When each grain is a single unit that is oriented differnently from the others and consists of 1000s of grains its called: polycrystalline
a difference in composition in the grains from the nucleus outward is known as: Coring
T or F small grain(fine) alloys tend to be weaker than large(coarse) grain alloys: F, small grain alloys are stronger due to there being more grain boundaries that stop the dislocation movement
Hardening Heat treatment(age hardening) results in what with respect to strength, hardness and ductility: higher strength and hardness

lower ductility
The process of melting a material that has been coldworked(eg. strain hardening) is called: annealing

this process can be used to decrease hardness and strength while increasing ductility
Know the difference between the time-temp curves of a pure metal versus an alloy: know it
page 3 of Metals/alloys handout
How are alloys classified: By use- crowns, inlays, remov partial dentures, implants
By major elements - Ag, Au, Co, Ni, Pd, Ti
by nobility - HN "high nobility", N "noble", and PB "predominantly base"
by principal elemnts - Au-Pd-Ag, Ni-Cr-Be, Ti-Al-V
by dominant phase system - peritectic, intermetallic, isomorphous, and eutectic
What is a physically distinct, homogenous mechanically separable portion of a system with a unique crystal structure and unique physical properties known as: Metallurgic phase
What are the 4 types of alloys: Solid solutions, Intermetallic, Eutectic, and Peritectic
When two or more pure metals are completely soluble in each other at all percentages what is it called: Complete solid solution
When limited amounts of one metal dissolve in another metal, the alloy formed is called what: limited solid solution
What are the 2 types of solid solutions: interstitial - atom of 2nd atoms is in lattice of 1st atom

substitutional - 2 different atoms substitute into spaces of solvents crystal lattice
What are the factors that determine the extent of solid solubility: atom size
valence
chemical affinity
crystal structure
Chemical compounds that result from solidification of 2 or more metals in near stoichiometric ratios are called: Intermetallic compounds

these are usually hard, brittle and have unpredictable properties
give some examples of intermetallic compounds used in dentistry: Ag3Sn, Ag2Hg2 in dental amalgams and Fe3C
Alloys formed from metals that are msicible in the liquid state but separate in the solid state are called: Eutectic alloys

these have a melting point instead of range, they are brittle, weak and have low corrosion resistance

Example Ag-Cu found in high copper spherical amalgam
When an alloy is made with two solid solutions that have limited solubility its called: peritectic alloy

these are brittle, weak and have low corossion resistance

also susceptible to coring where the cores have higher solidus temps and the surrounding matrix has compositions with lower temps

example Ag-Sn amalgams and Pt-Ag in casting alloys
an alloy containing grains of one phase that have a homogenous structure and are solid solution alloys are called: isomorphous alloys
Alloys can also be classified by number of elements give some examples: Binary alloy(2 elements)
Tertiary alloy(3 elements)
Quaternary(4 elements)
an alloy that contains mercury(Hg) is called an: Amalgam
what is the process of mixing Hg with other metals called: amalgamation
Whats the difference between dental amalgam alloy(Amalgam Alloy) and dental amalgam(amalgam): Dental Amalgam Alloy is an alloy made of Ag, Cu and Sn

while dental amalgam is an alloy containing Hg and Dental Amlagam Alloy
the forceful mixing of Hg and amalgam alloy powder is called: Trituration

is performed in triturator or amalgamator which can control the duration and amount of energy put into the capsule
What are the specifics for the ADA spec 1 amalgam: predominantly Ag and Sn
if > 0.01 wt% Zn its called zinc containing
if <= 0.01 wt% Zn its called non-zinc containing

copper content is not given in revised ADA spec #1
Whats another name for low copper amalgam alloys: lathe cut alloys
65% wt Ag, 29 wt% Sn and <6 wt% Cu
What are the 2 types of high copper amalgams: Spherical alloy - between 13-30 wt% Cu

Admixed alloy - between 9-20 wt% Cu
T or F products that condense well are harder to shape: F, the better the condensation the easier it is to shape
adding 4-5 wt% Cu as a substitute for Ag in the Ag-Sn system results in an alloy that is: harder and stronger and easier to comminute(mix)

Zinc makse the alloy less brittle and acts as a deoxidizer - "reducing agent"
The addition of Hg, In or Pd to the amalgam alloy compositino is for what purpose: to improve handling properties
How are both lathe-cut and spherical amalgams alloys manufactured: Lathe cut are ground in a lathe or milled

Spherical are cast by blowing molten alloy thru a nozzle to form small spheres(atomization)
How is admixed alloy manufactured: 45-60 wt% lathe cut plus 30-55 wt% spherical are added together
How are the grains of an amalgam alloy homogeninzed in manufacturing them: heat treatment

different methods of cooling the ingot produce different phases
treatment of the ground particles with ______ results in preferential dissolution of certain components and increases the reactivity of the particles: acid
Very small particles(< 3 micrometers) have a larger surface area per unit volume of powder and therefore requrire more: Hg
smaller particle sizes result in: rapid hardening and higher early strength and are less likely to get pulled out of the amalgam microstructure during carving or finishing, thus leaving behind a smoother surface that is less likely to corode
T or F spherical alloys resist condensation better than admixed and lather cut amalgams: F lathe cut and admixed resist condensation better

thus spherical amalgams are harder to adapt to contoured proximal surfaces
T or F spherical alloys require less Hg because they have smaller surface area per volume that lather cut alloys: T

low Hg content alloys usually have better properties
T or F Low Cu amalgams have better mechanical properties, corrosion resistance and marginal integrity than high Cu amalgams: F, High Cu amalgams have better mechanical properties, corrosion resistance and marginal integrity
During trituration of the alloy powder Hg disolves the surface of the alloy particles to form what: some new phases
Upon completion of trituration the setting reaction starts and the material hardens usually within what time period: 1 hour

any remaining liquid Hg is almost completely consumed in the seting reaction
know table 17-1 in the book: know phases, formulas and greek letter abbr.
What is the lathe cut(low copper) particle called in Ag-SN setting reaction for lathe cut alloys: gamma
Describe the setting reaction for lathe cut alloy: start with Ag-Sn complex

Ag goes into solution and reacts with Hg to form Ag2Hg3 (Gamma 1)this holds everything together

Sn goes into solution with Hg and forms Sn7-8Hg (Gamma2)this corrodes easily and is weak

Sn comines with Cu to form Cu3Sn (Epsilon)
What is formed in the lathe cut seeting reaction that we dont want but cant help but form: Gamma 2, it sucks, its weak and corrodes
Describe the setting reaction for single composition alloy Example Tytin System: Ag-Sn-Cu spherical(high copper) particle starting material

Ag goes into solution reacts with Hg to form Ag2Hg3 (gamma 1)

Sn goes into solution and very little or no Sn7-8Hg(Gamma2)is formed, instead Sn goes onto react with Cu to form Cu6Sn5 (Eta) which does not corrode

Cu enters solution and preferentially reacts with Sn to form Cu6Sn5 (Eta)
Describe the setting reaction for Admixed alloy: start out with both Ag-Sn lathe cut(low Cu)particle and Ag-Sn-Cu spherical(high Cu) particles

The Ag-Sn can take 2 paths
Ag goes into solution to react with Hg and make Ag2Hg3 (gamma1)
while the Sn reacts with Hg to make Sn7-8Hg (gamma2) DONT FEAR THIS BAD BYPRODUCT IS USED UP BY THE Ag-Sn-Cu side of things

Ag-Sn-Cu
the Cu enters solution and preferentially reacts with the Sn-Hg created from above and forms Cu6Sn5(Eta) + Hg
Now this Hg reacts with the free Ag from the Ag-Sn-Cu to make AgHg(gamma 1)
Most modern amalgams show net contraction in first how many hours: 24

ADA spec #1 limits it to 20 micrometers/cm change
If there is sufficient Hg in the matrix the outward growth of what can cause expansion: Gamma1
Contraction or expansion of amalgam depends on what 2 factors: manipulation and how much it is constrained
What can cause contraction of the amalgam: higher condensation pressures, lower Hg to alloy ratios, longer trituration times and smaller particle size

NOTE opposites of all these can cause expansion
exposure of a zinc containing amalgam to water after trituration or condensation can cause what: gradual expansion

its caused by formation of H2 gas in the restoration which drives internal pressure up and subsequent creep occurs

occurs after 24 hours typically after 3-5 days
To prevent delayed expansion of the amalgam due to exposure to water after trituration what precaution should be taken: use a rubber dam
T or F Amalgam is a brittle material that is weaker in compression than tension: F amalgam is weaker in tension(48-70 MPa) than to compression(310-510 MPa)
What can affect the strength of an amalgam: Trituration, condensation, Hg content, porosities and hardening rate
What 2 things affect creep of an amalgam: Microstructure and manipulation
Who invented the minimal Hg technique in 1959: Eames
What are some of the ratios of the different amalgam mixtures(hg/alloy): Contemporary lathe-cut 50/50
spherical 42/58
admixed 48/52
what can happend to an amalgam that is Hg rich: expansion, lower strength, increase creep and marginal breakdown
What can happen to an Hg poor amalgam: contracts, low strength, corrodes easily and is rough
know the different things that happen to the amalgams if you have low Hg high Hg over mixed, under mixed: see picture on last page of Amalgam 1 handout
If Hg and alloy are mixed to long(overtriturated) what happens: more alloy is forced to dissolve
more reaction product is formed
product has smaller volume than components
build up heat
mechanical energy keeps crystal from growin and hitting(no expansion)
material is weaker, has excessive contraction and sets faster
If Hg and alloy not mixed long enough what happens: little disolution of alloy into Hg
small portion of reaction occurs
crystals formed can grow and hit each other
material is grainy, weak, shows high expansion, sets slower, is rougher and corrodes and tarnishes easily
What is the maximum of creep allowed by ADA: 2%
What are the purposes of condensation: adaptation of amalgam to cavity wall
decrease amount of residual Hg MORE Hg MEANS DIMINISHED PHYSICAL PROPERTIES
decrease number of voids because fewer voids results in better physical properties
Causes layers of amalgam to adhere
T or F the longer the time before trituration and condensation the stronger the amalgam is: F, the more time between trituration and condensation the weaker the amalgam will be
Describe how condensation should be performed: start at the center of the restoration and stepped toward margins, perform it in small increments to reduce void formation and improve adaptation
Condensation pressure is increased/decreased with a condenser of smaller diameter: increased
P - F/A if A is getting smaller then F is getting larger
What reproduces a tooths missing anatomy and occlusal function: Carving

done after completion of initial set(5 minutes)
What helps bring Hg to surface, smooths surface and helps adapt margins of restoration with tooth strucutre to reduce microleakage: Burnishing
a mechanical process by which gross irregularities are reduced and desired contours are developed is known as: Finishing
What are the steps for polishing amalgams: flour of pumice with rubber dam
tin oxide or Amalgloss
wait 24 hours before polishing so that it has adequate compressive strength
T or F you should use the leading edge when doing your amalgam polish: F, the leading edge can lead to gouges in the amalgam
T or F tarnish(black Ag2S) means that there is active corrosion on the amalgam: F
The type of corrosion to an amalgam that helps seal the interface and stop microleakage is usually caused by: Crevice Corrosion
T or F high Cu alloys form corroson products more slowly: T
What restorations in either proximal or occlusal contact with amalgams can cause galvanic corrosion: Gold
amalgam is considered to be: technique insensitive

even our dumbasses cant fuk it up
What must be laid down below the amalgam since amalgams are good conductors of heat: insulator "base" cement
What can result in hypomargination: carving to soon

if patient bites to soon you can get fractures of amgalgams
T or F high Cu alloys have shorter average lives than low Cu alloys: F, High Cu have longer lives
T or F Zn containing alloys have higher life expectancy than non zinc alloys: T
The worst survival rates are seen in what alloys: low Cu non Zn
Factors that the dentist controls on the overall quality of an amalgam restoration: Selection of alloy
Hg:alloy ratio
Trituration procedure
condesation technique
marginal integrity
antatomical characteristics
finsihing procedure
Manufacturer controlled factors that determine amalgam quality: composition of alloy
heat treatment of alloy
manufacturing method
surface treatment of particles
form of supply of alloy
What is the maximum safe environmental concentration allowed in the dental office: 0.05 mg/m3(50 micrograms/meter cubed)
How is Hg absorbed in humans: ingestion, inhalation, and thru the skin
What is the name for the allergic reaction of a patient to amalgams that lasts more than 2 weeks: Type IV Hypersensitivity - refer to allergist
T or F Mercury is volitile and has low surface tension: F, it has high surface tension which causes it to bead up on the floor if spilled
What are the 3 forms of mercury: elemental/metallic (Hg0)- absorbed via skin or by inhalation as vapor

Inorganic Ion(Hg2+) absorbed poorly in gut

Organic (Methyl or Ethyl Mercury)
Methyl produced by Hg0 bacteria and is most toxic form, its very efficiently absorbed in gut
What affects mercury toxicity and exposure: the form of mercury
Organic(methyl or ethyl mercury) is the most dangerous
how long is the half-life of mercury in the body: 20-90 days
Dont vacuum hg spill use clean up or spill kit: store amalgam in sealed container not in trash
use rubber dam and high speed evacuation when removing old amalgams
dont squeeze freshe amalgam with finger(mulling)

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