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57 Cards in this Set

  • Front
  • Back
what is the setting reaction for amalgam
Ag3Sn + Hg = Ag2Hg3 + Sn7-8Hg + Ag3Sn
what is the amalgam setting reaction in terms of gamma
gamma via trituration with mercury yields gamma 1+ gamma 2+ gamma
what is amalgam composed of and how does each element contribute to amalgam
-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
what do the following metals do to expansion, flow, and strength
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
what is comminution
when smaller particles of the alloy are created through shavings, filings, or ball mill filings
what does spherical alloys do to the strength of an alloy
it increases strength, BUT make it harder to carve
what is coworking
distortion of structures when resisting tensile forces, but this distortion wont stretch as far before it breaks (behaves more brittle)
what undoes coworking

(stress relieving and annealing can undo the stress that caused deformation)
what does increasing strength do...
decrease ductility
what is the latent heat of fusion
the kinetic energy required during cooling of metals (free molecular motion stops)
what is the microscopic appearance of casting alloys
crystalline and dendritic
what are the properties of Wrought alloys
high strength/hardness
decreased ductility with cold work
used for wires/bands/bars
microscopic structures is fibrous
what does annealing a metal allow
removal of induced stress
grain growth
what are the characteristics of alloy blends
change the physical properties of pure metals
change the hardness of metals
result in a melting range, not melting temp.
alloy blends can be classified as...
solid solutions
what is the purpose of bases, liners, and varnishes
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
what is dentin composed of (%)
10% water
70% inorganic (hydroxyapetite)
20% organic (type I collagen, phosphoproteins, proteoglycans)
how does the composition of enamel differ from denting
enamel has more ORGANIC components and 5 times the amount of WATER
what is the dentin smear layer and what is it made of
a 2-10 micron layer on tooth surface made of...
-denatured collagen
-broken hydroxyapetite
-smeared proteoglycans/phosphoproteins
if the dentin smear layer was removed with acids, what is exposed
dentin tubules
what does sensitivity arise from
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
what are varnishes made of
made of resins of NATURAL GUMS
(copal, urethane isocyanate, polyamide)
what is the role of varnishes
to seal dentin/amalgam tooth interface

**CANNOT be used under materials that have adhesive properties (like composites)
Do varnishes have theraputic effects?
They have little therapeutic effects
(primary function is to SEAL dentin-amalgam tooth interface)
what is the function of liners
limit leakages
where are liners applied to
-axial/pulpal walls (<0.5mm)
-not placed on the margins of restorations since that would be washed away with saliva
what are the 3 kinds of liners
calcium hydroxide
zinc oxide and eugenol (ZOE)
glass ionomers
what does calcium hydroxide liners do
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
what properties does modified ZOE display
-increased strength and reduced solubility
-can also promote secondary dentin due to slight irritation
what does glass ionomers release into dentin as a therapeutic benefit
release FLUORIDE as a therapeutic benefit to dentin
What can be a problem with glass ionomer liners over time
can SHRINK over time and therefore LEAK

(light cured models show LESS LEAKAGE over time)
when are bases used
when extensive amounts of tooth structure has been removed
what do bases do
-provide thermal insulation and restore the ideal cavity form
-show high strength, and can be used as temporary materials (like IRM= interim restorative materials)
what are some examples of bases
thick zinc phosphate
silicate cements
**calcium hydroxide is added to limit the acid production
what is adhesion
the bonding of dissimilar materials by the attraction of atoms/molecules
what is adhesion weakened by...
1. differences in thermal expansion
2. dimensional changes during adhesive setting
3. hydrolytic degradation of bond
what is chemical adhesion
bonding at the atomic/molecular level
what is mechanical adhesion
interlocking/penetration of surfaces
how does etching the enamel increase adhesion
*allows for more MECHANICAL adhesion to occur
*greater surface area for CHEMICAL adhesion to occur
what 2 things does hydroxyethyl methacrylate bind to
*dentin at one end and
*a hydrophobic composite at the other end
what are smear layers usually incorporated into
smear layers are usually incorporated into the restoration
what is the adhesion quotient (AQ)
*difference between SURFACE ENERGY and SURFACE TENSION
*the magic number is 0
what can contact areas be modified by
what is required for adhesion between phases
what is cohesion
force of attachment between atoms of the same material
what does composite strength depend on
1. geometry of the filler (irregular shapes allow for more chemical/mechanical bonding)
2. volume fraction on each phase
3. composition of each phase
what is the most common matrix phase for composite resins and what are its properties(polymerization shrinkage, and flow)
-polymerization shrinkage = 6.5%
-flow into cavity prep is difficult, because this is a VERY STIFF MATERIAL
What is the shrinkage of TEGMA
shrinkage = 10%
*when mixed with BIS-GMA = 8%
*addition of fillers makes shrinkage = 1%
what are the requirements for the particles of inorganic phase of composite resins
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
what are the properties that arise when filler particles are added
-tensile strength doesn't change
-HARDNESS is increased
describe the different stresses that arise between the INTERACTION of FILLER PARTICLES with MATRIX
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)
describe hybrid particles of composite restorations
-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
what is the grain size for glass ionomers
13-19 microns
Describe glass ionomer setting reaction
-acid attacks powder to release fluoride and cations
-interaction with anion forms gel matrix
-aluminum ions have stabilizing effect on matrix
what does acid from glass ionomers latch onto to bind it to enamel and dentin
acid latches onto calcium within the dental enamel
what are the properties of glass ionomer cements
-high compressive strength
-low tensile strength (compared to resin-based cements)
-higher solubility
-can cause prolonged hypersensitivity
what is glass ionomer cements used for
-primarily for permanent cementation as a base
-used on orthodontic bands