Cements 4 Flashcards
Compare resin based composites and acid-based cements like GIC
- resins are tougher, quick setting and insoluble
- GICs are brittle, slow setting, soluble and fluoride releasing
What was the first attempt at a hybrid material?
- composite with degradable glass filler
How did composite with degradable glass filler work?
- 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
Was composite with degradable glass filler successful?
- not an initial success
- alternatives made
- still active research made - potential for more to be released
What bridges the gap between composite to GIC?
- composites
- compomers 2nd
- giomers 3rd
- RM GICs 1st
- GICs
What is resin modified GIC?
- 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)
Setting reactions for resin modified GIC
- 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
Compare reaction rates of light activated, chemically activated polymerisation and acid base reaction
- light activated first
- then chemical activated
- then acid-base
Polymerisation stabilizes against …
moisture
- less moisture sensitive
Resin-modified glass ionomer applications
- direct filling for lining, base and luting
- light activated for lining and base applications (some luting apps)
- chemically activated for luting and orthodontics
Compare setting in resin modified GICs and GICs
polymerisation is faster than acid-base reaction
Compare fluoride release in resin modified GICs and GICs
- acid and base reaction liberates fluoride
- lower levels released than GIC
- can be recharged
Compare adhesion in resin modified GICs and GICs
- COO- can still react with calcium ions
- limited by lower acid group content
- maybe not as high as GICs
- bonding agent often required
How does polymerisation of RMGIC affect solubility?
- polymerisation leads to a lower initial solubility
- faster reaction produces crosslinked network
- no need to apply varnish during setting or when doing subsequent work
Mechanical properties are better in GIC or RMGIC?
- better in GICs
- properties are worse than composites
Dimensional changes in RMGIC
- 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
Disadvantages of water absorption in RMGIC
- can cause swelling/pressure, degradation or discolouration
What are compomers?
- acid-modified composites
- similar to RMGIC
- strontium fluorisilicate glass - radio-opaque
- UDMA modified with acid groups
- hydrophilic monomer - HEMA or glycerol dimethacrylate
- no water
Are compomers light activated or chemically?
- light for restoratives
- chemical for luting
Setting reactions in compomers
- 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
Fluoride release from compomers
- some fluoride release may occur in water uptake
- most significantly in acid base reaction though
Structure of compomers
- matrix resin with acid
- water
- reactive glass filler
Role of HEMA in compomer
- 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
Manipulation characteristics in compomers
- good
- flow well and adapt to cavity easily
- tend to not stick to instruments
Mechanical properties of compomers
- similar to composites of equivalent filler concentration
- may deteriorate - aging effect
Fluoride release in compomers
- limited by acid base reaction
- no burst effect like in GICs
- sustained
Dimensional stability in compomers
- polymerisation reaction leads to shrinkage
What are compomer luting materials?
- 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
Compomer luting materials have greater … and … than acid base cements
- strength and toughness
Bonding of compomers
- 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
What are giomers?
- 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
2 main types of giomer
- S-PRG - surface reaction type glass filler
- F-PRG - full reaction type glass filler
Mechanical properties of giomers
- S-PRG similar to composite
- F type is weaker
Fluoride release in giomers
- due to GIC component
- minimal release and recharge in S-PRG
Water absorption in giomers
- F-PRG contains HEMA
- can lead to expansion in cavity
- radial pressure against cavity walls
Adhesion of giomers
- requires adhesives
- similar to composites
