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57 Cards in this Set
- Front
- Back
what is the setting reaction for amalgam
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Ag3Sn + Hg = Ag2Hg3 + Sn7-8Hg + Ag3Sn
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what is the amalgam setting reaction in terms of gamma
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gamma via trituration with mercury yields gamma 1+ gamma 2+ gamma
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what is amalgam composed of and how does each element contribute to amalgam
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-silver (67-74%): for strength/hardness
-tin (25-28%): aids in amalgamation....reduces corrosion resistance -copper (0-10%): for strength/hardness...creates uniform setting time -zinc: oxide scavenger |
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what do the following metals do to expansion, flow, and strength
1.silver 2.copper 3.zinc 4.tin 5.mercury |
1. silver: increase, decrease, increase
2. copper: increase, decrease, increase 3. zinc: decrease, N/A, decrease 4. tin: decrease, increase, decrease 5. mercury: increase, increase, decrease |
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what is comminution
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when smaller particles of the alloy are created through shavings, filings, or ball mill filings
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what does spherical alloys do to the strength of an alloy
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it increases strength, BUT make it harder to carve
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what is coworking
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distortion of structures when resisting tensile forces, but this distortion wont stretch as far before it breaks (behaves more brittle)
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what undoes coworking
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heat-treating
(stress relieving and annealing can undo the stress that caused deformation) |
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what does increasing strength do...
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decrease ductility
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what is the latent heat of fusion
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the kinetic energy required during cooling of metals (free molecular motion stops)
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what is the microscopic appearance of casting alloys
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crystalline and dendritic
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what are the properties of Wrought alloys
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high strength/hardness
decreased ductility with cold work used for wires/bands/bars microscopic structures is fibrous |
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what does annealing a metal allow
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removal of induced stress
recrystalization grain growth |
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what are the characteristics of alloy blends
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change the physical properties of pure metals
change the hardness of metals result in a melting range, not melting temp. |
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alloy blends can be classified as...
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solid solutions
eutectic intermetallic |
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what is the purpose of bases, liners, and varnishes
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1. provides a seal between enamel/dentin and the restorative material
2. protects the pulp from bacteria, thermal change, and irritants 3. limits the microleakage at the margins, and into the dentin tubules |
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what is dentin composed of (%)
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10% water
70% inorganic (hydroxyapetite) 20% organic (type I collagen, phosphoproteins, proteoglycans) |
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how does the composition of enamel differ from denting
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enamel has more ORGANIC components and 5 times the amount of WATER
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what is the dentin smear layer and what is it made of
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a 2-10 micron layer on tooth surface made of...
-denatured collagen -broken hydroxyapetite -smeared proteoglycans/phosphoproteins |
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if the dentin smear layer was removed with acids, what is exposed
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dentin tubules
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what does sensitivity arise from
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1. Open dentin tubules, which increase they hydrodynamic flow
2. Bacteria leakage, which cause a change in pulpal morphology 3. restorative materials RARELY cause sensitivity |
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what are varnishes made of
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made of resins of NATURAL GUMS
(copal, urethane isocyanate, polyamide) |
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what is the role of varnishes
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to seal dentin/amalgam tooth interface
**CANNOT be used under materials that have adhesive properties (like composites) |
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Do varnishes have theraputic effects?
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They have little therapeutic effects
(primary function is to SEAL dentin-amalgam tooth interface) |
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what is the function of liners
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limit leakages
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where are liners applied to
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-axial/pulpal walls (<0.5mm)
-not placed on the margins of restorations since that would be washed away with saliva |
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what are the 3 kinds of liners
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calcium hydroxide
zinc oxide and eugenol (ZOE) glass ionomers |
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what does calcium hydroxide liners do
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1. irritate pulp to form secondary (sclerotic) dentin to seal tubules
2. kill most bacteria due to high pH **material is applied to surface of dentin |
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what properties does modified ZOE display
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-increased strength and reduced solubility
-can also promote secondary dentin due to slight irritation |
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what does glass ionomers release into dentin as a therapeutic benefit
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release FLUORIDE as a therapeutic benefit to dentin
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What can be a problem with glass ionomer liners over time
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can SHRINK over time and therefore LEAK
(light cured models show LESS LEAKAGE over time) |
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when are bases used
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when extensive amounts of tooth structure has been removed
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what do bases do
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-provide thermal insulation and restore the ideal cavity form
-show high strength, and can be used as temporary materials (like IRM= interim restorative materials) |
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what are some examples of bases
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thick zinc phosphate
silicate cements **calcium hydroxide is added to limit the acid production |
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what is adhesion
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the bonding of dissimilar materials by the attraction of atoms/molecules
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what is adhesion weakened by...
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1. differences in thermal expansion
2. dimensional changes during adhesive setting 3. hydrolytic degradation of bond |
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what is chemical adhesion
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bonding at the atomic/molecular level
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what is mechanical adhesion
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interlocking/penetration of surfaces
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how does etching the enamel increase adhesion
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*allows for more MECHANICAL adhesion to occur
*greater surface area for CHEMICAL adhesion to occur |
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what 2 things does hydroxyethyl methacrylate bind to
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*dentin at one end and
*a hydrophobic composite at the other end |
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what are smear layers usually incorporated into
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smear layers are usually incorporated into the restoration
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what is the adhesion quotient (AQ)
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*difference between SURFACE ENERGY and SURFACE TENSION
*the magic number is 0 |
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what can contact areas be modified by
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surfactants
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what is required for adhesion between phases
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wettability
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what is cohesion
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force of attachment between atoms of the same material
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what does composite strength depend on
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1. geometry of the filler (irregular shapes allow for more chemical/mechanical bonding)
2. volume fraction on each phase 3. composition of each phase |
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what is the most common matrix phase for composite resins and what are its properties(polymerization shrinkage, and flow)
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BIS-GMA
-polymerization shrinkage = 6.5% -flow into cavity prep is difficult, because this is a VERY STIFF MATERIAL |
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What is the shrinkage of TEGMA
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shrinkage = 10%
*when mixed with BIS-GMA = 8% *addition of fillers makes shrinkage = 1% |
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what are the requirements for the particles of inorganic phase of composite resins
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1. refractive index must be close to that of tooth structure
2. must be radiopaque 3. coefficient of thermal expansion must be similar to tooth |
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what are the properties that arise when filler particles are added
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-tensile strength doesn't change
-HARDNESS is increased -increases WEAR RESISTANCE -reduces COEFFICIENT OF THERMAL EXPANSION |
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describe the different stresses that arise between the INTERACTION of FILLER PARTICLES with MATRIX
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Hoop Stress= matrix will shrink around the particle
Interparticle Stress= occurs between particles...pulls matrix away from the particles (the weakest link between the bond and resin) |
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describe hybrid particles of composite restorations
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-combined microfilled and small particles (0.5-5 microns in size)
-microfilled particles insert themselves between small particles **this delays the time it takes to fracture, and increases overall strength |
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what is the grain size for glass ionomers
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13-19 microns
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Describe glass ionomer setting reaction
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-acid attacks powder to release fluoride and cations
-interaction with anion forms gel matrix -aluminum ions have stabilizing effect on matrix |
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what does acid from glass ionomers latch onto to bind it to enamel and dentin
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acid latches onto calcium within the dental enamel
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what are the properties of glass ionomer cements
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-high compressive strength
-low tensile strength (compared to resin-based cements) -higher solubility -can cause prolonged hypersensitivity |
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what is glass ionomer cements used for
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-primarily for permanent cementation as a base
-used on orthodontic bands |