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Dental Materials > Cements 4 > Flashcards

Cements 4 Flashcards

1
Q

Compare resin based composites and acid-based cements like GIC

A
  • resins are tougher, quick setting and insoluble
  • GICs are brittle, slow setting, soluble and fluoride releasing
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2
Q

What was the first attempt at a hybrid material?

A
  • composite with degradable glass filler
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3
Q

How did composite with degradable glass filler work?

A
  • fluoride release initially high (not as high as GIC)
  • tails off over days/weeks, related to the glass on the surface
  • once exhausted, no more release
  • filler degrades over time reducing the mechanical properties
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4
Q

Was composite with degradable glass filler successful?

A
  • not an initial success
  • alternatives made
  • still active research made - potential for more to be released
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5
Q

What bridges the gap between composite to GIC?

A
  • composites
  • compomers 2nd
  • giomers 3rd
  • RM GICs 1st
  • GICs
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6
Q

What is resin modified GIC?

A
  • combination of GIC ingredients (glass powder, polyacids, water)
  • with monomers (similar to composites UDMA) hydrophilic monomers/HEMA, initiators (all have photo-initiators, some have chemical ones)
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7
Q

Setting reactions for resin modified GIC

A
  • acid and base reaction - from mixing powder with liquid
  • polymerisation (light or chemical activation)
  • once powder and liquid are mixed, acid base reaction begins. If chemically activated, polymerisation begins
  • light activated polymerisation delayed until light is switched on
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8
Q

Compare reaction rates of light activated, chemically activated polymerisation and acid base reaction

A
  • light activated first
  • then chemical activated
  • then acid-base
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9
Q

Polymerisation stabilizes against …

A

moisture
- less moisture sensitive

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10
Q

Resin-modified glass ionomer applications

A
  • direct filling for lining, base and luting
  • light activated for lining and base applications (some luting apps)
  • chemically activated for luting and orthodontics
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11
Q

Compare setting in resin modified GICs and GICs

A

polymerisation is faster than acid-base reaction

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12
Q

Compare fluoride release in resin modified GICs and GICs

A
  • acid and base reaction liberates fluoride
  • lower levels released than GIC
  • can be recharged
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13
Q

Compare adhesion in resin modified GICs and GICs

A
  • COO- can still react with calcium ions
  • limited by lower acid group content
  • maybe not as high as GICs
  • bonding agent often required
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14
Q

How does polymerisation of RMGIC affect solubility?

A
  • polymerisation leads to a lower initial solubility
  • faster reaction produces crosslinked network
  • no need to apply varnish during setting or when doing subsequent work
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15
Q

Mechanical properties are better in GIC or RMGIC?

A
  • better in GICs
  • properties are worse than composites
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16
Q

Dimensional changes in RMGIC

A
  • initial shrinkage on setting - polymerisation causes volumetric contraction
  • long-term expansion as HEMA is hydrophilic and absorbs water
  • ISO 4049 has the maximum allowed water absorption, RMGICs have higher absorption
17
Q

Disadvantages of water absorption in RMGIC

A
  • can cause swelling/pressure, degradation or discolouration
18
Q

What are compomers?

A
  • acid-modified composites
  • similar to RMGIC
  • strontium fluorisilicate glass - radio-opaque
  • UDMA modified with acid groups
  • hydrophilic monomer - HEMA or glycerol dimethacrylate
  • no water
19
Q

Are compomers light activated or chemically?

A
  • light for restoratives
  • chemical for luting
20
Q

Setting reactions in compomers

A
  • stage 1 is polymerisation (light or chemical)
  • stage 2 is water uptake from oral env - gives ionic environment
  • stage 3 is acid base reaction - glass and aqueous acid
21
Q

Fluoride release from compomers

A
  • some fluoride release may occur in water uptake
  • most significantly in acid base reaction though
22
Q

Structure of compomers

A
  • matrix resin with acid
  • water
  • reactive glass filler
23
Q

Role of HEMA in compomer

A
  • allows water to enter matrix and therefore further acid-base reaction and fluoride release
  • can lead to a gap forming around glass particles which weakens the compomers over time
24
Q

Manipulation characteristics in compomers

A
  • good
  • flow well and adapt to cavity easily
  • tend to not stick to instruments
25
Q

Mechanical properties of compomers

A
  • similar to composites of equivalent filler concentration
  • may deteriorate - aging effect
26
Q

Fluoride release in compomers

A
  • limited by acid base reaction
  • no burst effect like in GICs
  • sustained
27
Q

Dimensional stability in compomers

A
  • polymerisation reaction leads to shrinkage
28
Q

What are compomer luting materials?

A
  • chemically activated products for luting
  • normally a powder-liquid e.g Dyract Cem
  • similar to restoratives with same brand name
  • air block gel to prevent oxygen inhibition
  • resin cement with some fluoride release
  • chemically activated polymerisation - minimal acid base reaction
29
Q

Compomer luting materials have greater … and … than acid base cements

A
  • strength and toughness
30
Q

Bonding of compomers

A
  • don’t naturally bond to enamel and dentine
  • too viscous, insufficient free acid groups in resin, insufficient ionic character (no water)
  • needs a dentine bonding agent - equivalent to composite, required for restoration and luting applications
31
Q

What are giomers?

A
  • composite with pre-reacted glass ionomer glass filler
  • acid and glass pre-reacted by manufacturer
  • particles surface treated to aid mechanical properties
  • blend with resin to form composite
32
Q

2 main types of giomer

A
  • S-PRG - surface reaction type glass filler
  • F-PRG - full reaction type glass filler
33
Q

Mechanical properties of giomers

A
  • S-PRG similar to composite
  • F type is weaker
34
Q

Fluoride release in giomers

A
  • due to GIC component
  • minimal release and recharge in S-PRG
35
Q

Water absorption in giomers

A
  • F-PRG contains HEMA
  • can lead to expansion in cavity
  • radial pressure against cavity walls
36
Q

Adhesion of giomers

A
  • requires adhesives
  • similar to composites

Dental Materials (17 decks)

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