Dental Materials Science Exam Materials Flashcards

Terms Definitions
Gypsum~ Powder Form
calcium sulfate hemihydrate
a hemihydrate
dental stonewell formed crystals, dense, more regular
American National Standards Institute standards developed by the ADA Standards Committee on Dental Products are adopted by ANSI and designated as what type of specifications?
ANSI/ADA Specifications
material loss by dissolutiion of surface is called
Solubility
Force that cause attraction between two unlike molecules is what?
Adhesion
Very small particles(< 3 micrometers) have a larger surface area per unit volume of powder and therefore requrire more
Hg
sharply localized corrosion on base metals in presence of chlorides, resulting in pinpoint break down of passivating oxide film is called
Pitting Corrosion
Covalently bonded oxygen and hydrogen atoms creat dipoles whose charged poles attract each other in bonds known as what?
hydrogen bonds
"Basic research leads to new knowledge. It provides scientific capital. It creaes the fund from which the practical applications of knowledge must be drawn." was said by whom?
Vannevar Bush
the resistance of a material to indentation is called?
Hardness
an internal force that resists an external load or force thats measured per unit area is called
Stress
Who invented the minimal Hg technique in 1959
Eames
failure at the interface between 2 materials that are bonded is known as what?
Adhesive failure
The use of rotary dental stone to close the open margins of a metal crown on a die is called what?
Burnish
the stress value that is calculated using the initial cross sectional area of the object before it is tested is called
Engineering Stress
amalgam is considered to be
technique insensitiveeven our dumbasses cant fuk it up
the presence of metallic bonds allows metals to readily what with heat and electricity
conduct them
What is the maximum of creep allowed by ADA
2%
This type of bond involves sharing of electrons, sp3 configurations and is usually seen in organic materials like polymers. it results in a precise directional orientation and typically has open structures with low densities and easily deforms at high te
Covalent Bonds
Name 5 chemical properties of matter.
Galvanism, Solubility, Adsorption, Absorption and Tarnish and Corrosion
The 2 types of adhesion are:
Primary(chemical) bonding - chemisorptionSecondary(physical) bonding - physisorption
When a material cannont return to its original shape it is considered
plastic shear
what are the conditions nescessary for electrochemical corrosion?
Metal oxidation and reductionElectrolytic contact between anode and cathodelow electrical resistance between anode and cathode
change in shape of a material that has been stressd so that normal interatomic equilibrium can be restored is called.
Structural Relaxation
the smallest unit in a space lattice that can be repeated in 3-D to produce a crystal structure is called a what?
unit cell
The type of corrosion to an amalgam that helps seal the interface and stop microleakage is usually caused by
Crevice Corrosion
When limited amounts of one metal dissolve in another metal, the alloy formed is called what
limited solid solution
Common types of forces include
Tensile <- ->Shear \/ /\compressive -> <-torsional - rotation about an axisflexural - like a bridge between 2 pointsbending - just one point fixed other end bends like a diving board
If you remove a metal crown from a die before you burnish it, what will the metal margins exhibit if the elastic strain is exceeded?
Plastic strain
What did Taveau invent?
Likely to have invented First dental amalgam in 1816 in france
Atoms at the surface of a SOLID have a (higher or lower) energy state than those within the material due to non-uniform forces acting upon them. this condition leads to a force called what?
HigherSurface Energy
A liquid that becomes less viscous under pressure is called?
Thixotropicexamples are prophylaxis pastes, resin cements, gypsum and some impression materials
A noncrystalline structure that has short range order(i.e. the arrangement of crystals is interspersed by disordered units) is called what?
Amorphous solid or supercooled liquid
What 2 things affect creep of an amalgam
Microstructure and manipulation
When dendrites meet during growth, they form what
grain boundarythis demarcates each individual crystal(called a grain)
What are the factors that determine the extent of solid solubility
atom sizevalence chemical affinitycrystal structure
What are the 4 types of alloys
Solid solutions, Intermetallic, Eutectic, and Peritectic
the measure of heat transferred through a material by conductive flow is?
Thermal Conductivitykappa = J * Change in X/ Change in TempJ is heat fluxUnits cal/cm*s*deg C, W/m*K
True or false Hardness Comparisons of materials with similar compostions is acceptable.
True, however comparisons across material types are not valid
Inlay gold alloy contains what elements
Au, Cu, Ag, Pt and/or Pd
the property related to the rigidity of a material under stress is called
Modulus of Elasticityalso called Youngs Modulus and its the ratio of Engineering Stress to Strain and is denoted by EE = sigma/funny looking Eequivalent to stress/strainUnits same as stress cause funny looking E is deminsionless
Differnces that can lead to corrosion include
Chemical compostion and EMFMetallic ion concentration in an elctrolytedepolarization, due to different concentration of the electrolyte in gasseous oxygen
4 types of viscous materials are
Newtonian - shear stress proportional to shear strain so viscosity is constantPlastic - initial shear stress level has to be reached, then behaves like newtonian fluidDilatant - increase in viscosity as shear rate increases(more difficult to mix as rate of mixing increases)Pseudoplastic - decrease in viscosity as shear rate increases(easier to mix as rate of mixing increases)
exposure of a zinc containing amalgam to water after trituration or condensation can cause what
gradual expansionits caused by formation of H2 gas in the restoration which drives internal pressure up and subsequent creep occursoccurs after 24 hours typically after 3-5 days
What affects mercury toxicity and exposure
the form of mercuryOrganic(methyl or ethyl mercury) is the most dangerous
How do crystal dendrites form
they form outward from the nucleus, appearing like snowflakes
How are dental materials used in the mouth?
Restoration and replacement of damaged tooth/oral structures. IE fillings, bridges, crowns and dentures
give some examples of intermetallic compounds used in dentistry
Ag3Sn, Ag2Hg2 in dental amalgams and Fe3C
Give the name and symbol for each of the following measurment units.Lengthmasselectrical currentthermodynamic temp.amount of substanceluminous intesitytime
meter mkilogram kgampere Akelvin Kmole molcandela cdsecond s
The value of stress at which a small amount of predetermined plastic strain has occurred is called?
Yield Strength(Proof Test)Note: yield strength is used to determine the exact point on the stress-strain curve at which linearity ends. typical values of percent offset are .1-.2% plastic strain
give examples of each type of bonds in dental materials
Ionic - sodium fluoride, sodium chloride, gypsum, phosphate cementCovalent- silicon dioxide, carbon, dental resinsMetalic- Silver, goldVan der Waals - resins like polyethelyne, polymethylmethacrylateHydrogen - water sorption by dental resin
T or F spherical alloys resist condensation better than admixed and lather cut amalgams
F lathe cut and admixed resist condensation betterthus spherical amalgams are harder to adapt to contoured proximal surfaces
an intimate atomic level mixture of 2 or more pure metals is called a what
AlloyNOTE alloys are usually stronger than their individual components
T or F spherical alloys require less Hg because they have smaller surface area per volume that lather cut alloys
Tlow Hg content alloys usually have better properties
If Hg and alloy not mixed long enough what happens
little disolution of alloy into Hgsmall portion of reaction occurscrystals formed can grow and hit each othermaterial is grainy, weak, shows high expansion, sets slower, is rougher and corrodes and tarnishes easily
What is the name of the group in the ADA that studies evaluates, and dessiminates info regarding safety, efficacy and promotional claims of dental therapeutic agents, materials, instruments and equipment?
Council on Scientifc Affairs formerly known as Council on Dental Materials, Instruments and Devices)
What are the 2 types of high copper amalgams
Spherical alloy - between 13-30 wt% CuAdmixed alloy - between 9-20 wt% Cu
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
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
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