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106 Cards in this Set
- Front
- Back
an element that ionizes positively in solution is called a
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Pure Metal
examples in dentsitry are gold, mercury, platinum, silver, tin, copper, zinc |
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the presence of metallic bonds allows metals to readily what with heat and electricity
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conduct them
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whats another name for metallic bonds
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electron "cloud" or "gas"
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How do metallic bonds form
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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"
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What are the characteristic properties of metals
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ability to conduct thermal energy and electricity, luster, high density and strenght, opacity, ability to undergo significant permanent deformation
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an intimate atomic level mixture of 2 or more pure metals is called a what
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Alloy
NOTE alloys are usually stronger than their individual components |
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What are the differences between pure metals and alloys
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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 |
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What is the melting range of ADA Class III gold
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932-960 deg C
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know the table and slide info for Solidification of Metals slide on 2nd page of Metals/Alloys handout
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know slide
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Nucleus formation that results from a random process that has equal probability of occuring anywhere in the melt is called
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homogenous nucleation
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When foreign bodies such as container walls or dust "seed" the nucleus and the formation of nuclei are not random its called what
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Heterogeous Nucleation
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The radius at which a nucleus of crystallization is formed is called
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Critical Radius
defined- is the radius when the resultant free energy decrease as radius increases |
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How do crystal dendrites form
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they form outward from the nucleus, appearing like snowflakes
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When dendrites meet during growth, they form what
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grain boundary
this demarcates each individual crystal(called a grain) |
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When each grain is a single unit that is oriented differnently from the others and consists of 1000s of grains its called
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polycrystalline
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a difference in composition in the grains from the nucleus outward is known as
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Coring
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T or F small grain(fine) alloys tend to be weaker than large(coarse) grain alloys
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F, small grain alloys are stronger due to there being more grain boundaries that stop the dislocation movement
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Hardening Heat treatment(age hardening) results in what with respect to strength, hardness and ductility
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higher strength and hardness
lower ductility |
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The process of melting a material that has been coldworked(eg. strain hardening) is called
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annealing
this process can be used to decrease hardness and strength while increasing ductility |
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Know the difference between the time-temp curves of a pure metal versus an alloy
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know it
page 3 of Metals/alloys handout |
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How are alloys classified
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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 |
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What is a physically distinct, homogenous mechanically separable portion of a system with a unique crystal structure and unique physical properties known as
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Metallurgic phase
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What are the 4 types of alloys
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Solid solutions, Intermetallic, Eutectic, and Peritectic
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When two or more pure metals are completely soluble in each other at all percentages what is it called
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Complete solid solution
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When limited amounts of one metal dissolve in another metal, the alloy formed is called what
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limited solid solution
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What are the 2 types of solid solutions
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interstitial - atom of 2nd atoms is in lattice of 1st atom
substitutional - 2 different atoms substitute into spaces of solvents crystal lattice |
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What are the factors that determine the extent of solid solubility
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atom size
valence chemical affinity crystal structure |
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Chemical compounds that result from solidification of 2 or more metals in near stoichiometric ratios are called
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Intermetallic compounds
these are usually hard, brittle and have unpredictable properties |
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give some examples of intermetallic compounds used in dentistry
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Ag3Sn, Ag2Hg2 in dental amalgams and Fe3C
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Alloys formed from metals that are msicible in the liquid state but separate in the solid state are called
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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 |
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When an alloy is made with two solid solutions that have limited solubility its called
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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 |
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an alloy containing grains of one phase that have a homogenous structure and are solid solution alloys are called
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isomorphous alloys
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Alloys can also be classified by number of elements give some examples
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Binary alloy(2 elements)
Tertiary alloy(3 elements) Quaternary(4 elements) |
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an alloy that contains mercury(Hg) is called an
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Amalgam
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what is the process of mixing Hg with other metals called
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amalgamation
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Whats the difference between dental amalgam alloy(Amalgam Alloy) and dental amalgam(amalgam)
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Dental Amalgam Alloy is an alloy made of Ag, Cu and Sn
while dental amalgam is an alloy containing Hg and Dental Amlagam Alloy |
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the forceful mixing of Hg and amalgam alloy powder is called
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Trituration
is performed in triturator or amalgamator which can control the duration and amount of energy put into the capsule |
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What are the specifics for the ADA spec 1 amalgam
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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 |
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Whats another name for low copper amalgam alloys
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lathe cut alloys
65% wt Ag, 29 wt% Sn and <6 wt% Cu |
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What are the 2 types of high copper amalgams
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Spherical alloy - between 13-30 wt% Cu
Admixed alloy - between 9-20 wt% Cu |
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T or F products that condense well are harder to shape
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F, the better the condensation the easier it is to shape
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adding 4-5 wt% Cu as a substitute for Ag in the Ag-Sn system results in an alloy that is
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harder and stronger and easier to comminute(mix)
Zinc makse the alloy less brittle and acts as a deoxidizer - "reducing agent" |
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The addition of Hg, In or Pd to the amalgam alloy compositino is for what purpose
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to improve handling properties
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How are both lathe-cut and spherical amalgams alloys manufactured
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Lathe cut are ground in a lathe or milled
Spherical are cast by blowing molten alloy thru a nozzle to form small spheres(atomization) |
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How is admixed alloy manufactured
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45-60 wt% lathe cut plus 30-55 wt% spherical are added together
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How are the grains of an amalgam alloy homogeninzed in manufacturing them
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heat treatment
different methods of cooling the ingot produce different phases |
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treatment of the ground particles with ______ results in preferential dissolution of certain components and increases the reactivity of the particles
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acid
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Very small particles(< 3 micrometers) have a larger surface area per unit volume of powder and therefore requrire more
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Hg
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smaller particle sizes result in
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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
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T or F spherical alloys resist condensation better than admixed and lather cut amalgams
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F lathe cut and admixed resist condensation better
thus spherical amalgams are harder to adapt to contoured proximal surfaces |
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T or F spherical alloys require less Hg because they have smaller surface area per volume that lather cut alloys
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T
low Hg content alloys usually have better properties |
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T or F Low Cu amalgams have better mechanical properties, corrosion resistance and marginal integrity than high Cu amalgams
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F, High Cu amalgams have better mechanical properties, corrosion resistance and marginal integrity
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During trituration of the alloy powder Hg disolves the surface of the alloy particles to form what
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some new phases
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Upon completion of trituration the setting reaction starts and the material hardens usually within what time period
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1 hour
any remaining liquid Hg is almost completely consumed in the seting reaction |
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know table 17-1 in the book
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know phases, formulas and greek letter abbr.
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What is the lathe cut(low copper) particle called in Ag-SN setting reaction for lathe cut alloys
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gamma
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Describe the setting reaction for lathe cut alloy
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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) |
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What is formed in the lathe cut seeting reaction that we dont want but cant help but form
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Gamma 2, it sucks, its weak and corrodes
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Describe the setting reaction for single composition alloy Example Tytin System
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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) |
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Describe the setting reaction for Admixed alloy
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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) |
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Most modern amalgams show net contraction in first how many hours
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24
ADA spec #1 limits it to 20 micrometers/cm change |
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If there is sufficient Hg in the matrix the outward growth of what can cause expansion
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Gamma1
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Contraction or expansion of amalgam depends on what 2 factors
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manipulation and how much it is constrained
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What can cause contraction of the amalgam
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higher condensation pressures, lower Hg to alloy ratios, longer trituration times and smaller particle size
NOTE opposites of all these can cause expansion |
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exposure of a zinc containing amalgam to water after trituration or condensation can cause what
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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 |
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To prevent delayed expansion of the amalgam due to exposure to water after trituration what precaution should be taken
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use a rubber dam
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T or F Amalgam is a brittle material that is weaker in compression than tension
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F amalgam is weaker in tension(48-70 MPa) than to compression(310-510 MPa)
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What can affect the strength of an amalgam
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Trituration, condensation, Hg content, porosities and hardening rate
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What 2 things affect creep of an amalgam
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Microstructure and manipulation
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Who invented the minimal Hg technique in 1959
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Eames
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What are some of the ratios of the different amalgam mixtures(hg/alloy)
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Contemporary lathe-cut 50/50
spherical 42/58 admixed 48/52 |
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what can happend to an amalgam that is Hg rich
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expansion, lower strength, increase creep and marginal breakdown
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What can happen to an Hg poor amalgam
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contracts, low strength, corrodes easily and is rough
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know the different things that happen to the amalgams if you have low Hg high Hg over mixed, under mixed
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see picture on last page of Amalgam 1 handout
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If Hg and alloy are mixed to long(overtriturated) what happens
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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 |
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If Hg and alloy not mixed long enough what happens
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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 |
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What is the maximum of creep allowed by ADA
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2%
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What are the purposes of condensation
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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 |
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T or F the longer the time before trituration and condensation the stronger the amalgam is
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F, the more time between trituration and condensation the weaker the amalgam will be
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Describe how condensation should be performed
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start at the center of the restoration and stepped toward margins, perform it in small increments to reduce void formation and improve adaptation
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Condensation pressure is increased/decreased with a condenser of smaller diameter
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increased
P - F/A if A is getting smaller then F is getting larger |
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What reproduces a tooths missing anatomy and occlusal function
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Carving
done after completion of initial set(5 minutes) |
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What helps bring Hg to surface, smooths surface and helps adapt margins of restoration with tooth strucutre to reduce microleakage
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Burnishing
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a mechanical process by which gross irregularities are reduced and desired contours are developed is known as
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Finishing
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What are the steps for polishing amalgams
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flour of pumice with rubber dam
tin oxide or Amalgloss wait 24 hours before polishing so that it has adequate compressive strength |
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T or F you should use the leading edge when doing your amalgam polish
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F, the leading edge can lead to gouges in the amalgam
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T or F tarnish(black Ag2S) means that there is active corrosion on the amalgam
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F
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The type of corrosion to an amalgam that helps seal the interface and stop microleakage is usually caused by
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Crevice Corrosion
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T or F high Cu alloys form corroson products more slowly
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T
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What restorations in either proximal or occlusal contact with amalgams can cause galvanic corrosion
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Gold
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amalgam is considered to be
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technique insensitive
even our dumbasses cant fuk it up |
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What must be laid down below the amalgam since amalgams are good conductors of heat
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insulator "base" cement
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What can result in hypomargination
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carving to soon
if patient bites to soon you can get fractures of amgalgams |
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T or F high Cu alloys have shorter average lives than low Cu alloys
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F, High Cu have longer lives
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T or F Zn containing alloys have higher life expectancy than non zinc alloys
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T
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The worst survival rates are seen in what alloys
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low Cu non Zn
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Factors that the dentist controls on the overall quality of an amalgam restoration
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Selection of alloy
Hg:alloy ratio Trituration procedure condesation technique marginal integrity antatomical characteristics finsihing procedure |
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Manufacturer controlled factors that determine amalgam quality
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composition of alloy
heat treatment of alloy manufacturing method surface treatment of particles form of supply of alloy |
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What is the maximum safe environmental concentration allowed in the dental office
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0.05 mg/m3(50 micrograms/meter cubed)
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How is Hg absorbed in humans
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ingestion, inhalation, and thru the skin
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What is the name for the allergic reaction of a patient to amalgams that lasts more than 2 weeks
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Type IV Hypersensitivity - refer to allergist
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T or F Mercury is volitile and has low surface tension
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F, it has high surface tension which causes it to bead up on the floor if spilled
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What are the 3 forms of mercury
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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 |
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What affects mercury toxicity and exposure
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the form of mercury
Organic(methyl or ethyl mercury) is the most dangerous |
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how long is the half-life of mercury in the body
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20-90 days
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Dont vacuum hg spill use clean up or spill kit
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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) |