Biomat
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- 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
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 - 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
-
heat-treating
(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
recrystalization
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...
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solid solutions
eutectic
intermetallic - 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
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*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
- surfactants
- what is required for adhesion between phases
- wettability
- 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)
-
BIS-GMA
-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
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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 - what are the properties that arise when filler particles are added
-
-tensile strength doesn't change
-HARDNESS is increased
-increases WEAR RESISTANCE
-reduces COEFFICIENT OF THERMAL EXPANSION - 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) - 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 - 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