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DDS1-biomaterials > possible test questions > Flashcards

possible test questions Flashcards

1
Q

why void-free layer?

A

it is important to have a void-free layer (voids are detrimental to retention and support of prosthesis)

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2
Q

describe the ideal surface energy and wetting abilities in dental cements?

A

good wettability results from low surface energy cement and high surface energy substrate

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3
Q

how to measure wettability, what would be good wetting?

A
  • contact angle

- need a small contact angle for good wetting

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4
Q

why do bubbles form in gypsum?

A

if the surface tension of gypsum is higher than surface energy of impression material

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5
Q

what is the difference between luting and bonding

A

luting: no adhesive interaction, just a filler material
bonding: true adhesion between 2 materials

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6
Q

what is the reaction for glass ionomer cements

A

glass powder and PAA

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7
Q

why do we add tartaric acid to glass ionomers?

A

large molecules of polycarboxylate acid react with glass particles and dentine slowly, causing long maturation and susceptibility to moisture, so the tartaric acid shortens the setting time

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8
Q

benefits of tartaric acid?

A
  • short setting time
  • decrease viscosity of PAA
  • actively removes Al and Ca from glass
  • stabilizes matrix gelation
  • improves hardness and compressive/tensile strengths
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9
Q

describe the mechanism of fluoride release by glass ionomers?

A
  • rapid F release from matrix
  • gradual F release from particle overtime
  • if F is low, F is released from glass ionomer
  • if F is high, F is recharged into glass ionomer
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10
Q

describe the dual bonding mechanism of glass ionomer to dentin

A
  • chemical: displacement of phosphate/calcium ions from hydroxyapetite by carboxylate ions of polyacid and incorporation of carboxylate into hydroxyapetite structure
  • mechanical: micromechanical interlocking formed by shallow hybridization of partially demineralized dentin
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11
Q

advantages for glass ionomer

A
  • good fluoride release

- less shrinkage

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12
Q

disadvantages for glass ionomer

A
  • susceptible to dehydration
  • poor abrasion resistance
  • low esthetics and color-stability
  • less tensile strength than resins
  • poor acid resistance
  • sensitivity to moisture at placement
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13
Q

what is different about RMGI than GI

A
  • has a methacrylate copolymer

- covalent link between resin matrix and polyacrylic matrix

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14
Q

what is the purpose of acid etching?

A

dissolve the smear layer and mineral matrix of dentin and enamel so that resin can penetrate into enamel prisms and collage fibrils (micro-mechanical interlocking)

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15
Q

what is the significance of the hybrid layer

A
  • layer where adhesive resin infiltrates the primed demineralized dentin
  • forms an interfacial micro-mechanical bond
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16
Q

what is the disadvantage of using smaller diluent monomers

A

they under greater polymerization shrinkage, which increases the risk of leakage in marginal gaps

17
Q

why use a filler?

A
  • lower polymerization shrinkage
  • lower thermal expansion
  • lower water sorption
  • lower viscosity
  • reinforcement
  • radiopacity
18
Q

advantages of smaller particles in fillers?

A
  • less scattering of light
  • less opacity
  • better curing depth
  • smooth surface
  • less stains
19
Q

mechanism of silanes coupling agent

A
  • methoxy groups are hydrolyzed to silanol groups
  • silanol groups bind with other silanol groups on the filler surface (siloxane bonds)
  • methacrylate groups form covalent bond with resin by polymerization
20
Q

example of elastic materials

A
  • alginate
  • polysulfides
  • polyethers
  • silicones
21
Q

alginate, polyethers, and heavy-body PVS can be considered what?

A
  • mucocompressive

- irreversible setting

22
Q

compare chain growth with step growth

A
  • chain has vinyl groups, free radicals, fast prop and MW increase, no by product
  • step: difunctional monomers, no free radicals, slow prop and MW increase, by-product!
23
Q

why are elastomers elastic?

A

they have random coils that represent maximum entropy, if they get straightened, then the entropic recoiling effect will restore random coils

24
Q

why do polysac materials like alginate have poorer dimensional stability

A

-they only rely on 2 cross linking mechanisms: H bonding and chelation

25
Q

types of elastomeric impression

A
  • polysulfides
  • condensation silicones
  • polyethers
  • addition silicones (PVS)
26
Q

why do materials undergoing step growth have polymerization shrinkage and dimensional changes

A

ethanol evaporation

27
Q

disadvantages of condensation PVS

A
  • lack of dimensional stability (ethanol evap)
  • short working time
  • long setting time
  • 1-3% permanent deformation
  • hydrophobic
  • pour in 1 hour
28
Q

addition PVS is better because

A
  • no ethanol or byproduct so no shrinkage/dimensional changes
  • also hydrophobic, but you can add surfactant!
29
Q

other advantages of addition PVS

A
  • highly accurate
  • high dimensional stability
  • pour in 1 week
  • multiple casts
  • easy to mix
  • pleasant odor
30
Q

disadvantages of addition pvs

A
  • expensive
  • sulfur INHIBITS set (found in latex gloves and retraction soln)
  • short working time
  • hydrophobic
31
Q

polyethers - also addition!!!

A

alkyl benzene sulfonate + imine => carbocation

32
Q

advantages of polyether

A
  • accurate and good dimensional stability
  • HYDROPHILIC! so it has good wettability and tolerates moisture WITHOUT bubbles
  • 3 days
33
Q

disadvantages of polyether

A
  • rigid

- HYDROPHILIC - dimensional changes when absorbs water

34
Q

what factors can decrease working time and setting time

A
  • increase in temp
  • increase in humidity
  • increase in viscosity
35
Q

setting time (greatest to least)

A

condensation and polysulfide > polyether > addition (VPS)

36
Q

time for pouring the impression

A

condensation - 1 hour
addition - 1 week
polyether - 3 days

37
Q

best way to remove impression

A

“snap” removal - fast and least amount of plastic deformation

38
Q

explain the paradox of hydrophilic vs hydrophobic materials

A

hydrophilic can capture better details of surfaces because it can handle residual moisture better, but has poor dimensional stability because it absorbs water, while hydrophobic materials have better dimensional stability

39
Q

how do we solve the issue of hydrophobic and hydrophilic materials

A

add surfactant to hydrophobic materials to make the surface more hydrophilic, so it is more accurate but also has dimensional stability

DDS1-biomaterials (7 decks)

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