CSA glass polyalkenotes Flashcards
how do we activate glass polyalkenoate?
Chemical activation
what is light AND chemical activation for?
- Fissure sealants
- Dental composites
- Polyacid Modified Resins
- Resin modified polyalkenoate
What are glass polyakkenoates aka glass ionomer cements?
composite & comprised of 3 distinct components in the reacted (set) material
o Polymer
o Silica gel
o Ionomer glass
What is the setting reaction?
ionomer glass & polyacrylic acid packaged together & are mixed with liquid (water)
What is the chemical activation once powder and liquid have mixed?
polymer chains acidic:
o Polyacid + Base > Polysalt + water
What are polysalts formed made into?
cohesive solid glass polyalkenoate cements
What are the specifics of setting reaction ?
- acid dissolves in water forming a viscous aqueous solution with glass dispersed
- H+ ions displaced from polyacid then displace cations on surface of glass
- cations migrate away and react with negatively charged polymer ions
- modified glass surface becomes silica gel; reaction continues as further ions diffuse through gel to surface
What happens when cations migrate away and react with negative polymer ions?
Cross linking them to become long polymer chains (Polysalts)
When does GIC reach full strength?
after 1 week, petr. jelly used to reduce cracking after a week
What does GPAC do?
- Releases fluoride
- GPAC acts a fluoride sponge
- GPAC reacts with calcium ions in tooth
What does GPAC releasing fluoride react wtih?
neighbouring HAP tooth tissue forming fluroapatite, has greater acidic resistance and prevent secondary caries
What does GPAC fluoride sponge do?
absorbing fluoride from toothpaste etc. and then release it over a longer period of time
What happens when GPAC reacts with calcium ions?
- create direct chemical bond with GPAC & tooth
- seals the surface between the 2 materials, preventing entry of microbes
How to improve strength of GPAC?
- hybrid of GPAC known as cermets
- copolymer of polyvinyl phosphoric acid + polyacrylic acid
What are disadvantages of GPAC?
- Wear resistance is poor
- too opaque
- grey appearance of cermets
What can’t GPAC be used on?
occlusal surfaces for restorations
What are the advantages of GPAC?
- No cavity prep
- used as intermediate material > under amalgam or composite
- Good as a luting cement
how is structure of dental composites different to GPAC?
glass in glass polyalkenotes is inert & plays no part in the addition reaction
Why is inert filler included in structure?
- Decreases shrinkage of polymer & shrinkage of composite overall
- Decreases swelling due to water absorption & chance of staining.
- Decreases thermal expansion > Dec risk of tooth fracture >Dec sensitivity
- Fillers improve strength, increase young’s modulus, increase wear resistance, better aesthetics of composite
What does a decrease in shrinkage of polymer do?
decreases risk of tooth fracture
What does high coefficient of polymer mean?
o Decreases sensitivity caused by fluid movement in tubules
What is microfilled composite?
o Smaller filler used to improve surface finish
o incr. filler SA, more matrix required to produce workable product
What is hybrid composite?
o Mixture of conventional (5-10 micrometres) intermediate and small (0.04 micrometre) fillers
o 75-85% by volume of filler
What is the polymer matrix?
Bisphenol glycidyl methacrylate (Bis-GMA) blended with urethane dimethacrylate (UDMA)
What are drawbacks of composites?
- Blue light used to cure so built up incrementally
- Blue light bulb ages
- Material is hydrophobic so needs to be dry
- Doesn’t bond to teeth so bonding agent required
- Polymerisation shrinkage
Why do we build up incrementally ?
reduce shrinkage and RO fracture
What does polymerisation shrinkage lead to?
bacterial ingress so prone to recurrent caries
What are current bonding agents?
unfilled resin which is diluted with a carrier which may be hydrophilic
What does etch remove?
SMear layer created by cavity prep
What is smear layer?
layer of debris caused by cutting into dentine which blocks tubules
How is mechanical bonding achieved ?
tags forming, enter dentinal tubules
Whys is silaine coupling agent added to surface of glass filler?
filler & matrix will bond
What are resin modified polyalkenoates?
light cured glass ionomers where polyacid modified to have functional groups
How is RMGIC different to GPAC?
polished immediately after light activated reaction therefore less susceptible to desiccation
What is HEMA Hydroxyethyl methacrylate used for
addition polymerisation cross links
What are polyacid modified resins (compomers) ?
o Dental composite precursors changed so have acid groups
- material is light activated
What happens once compomers take in water from saliva?
causes disassociation of acid groups
- acid base reaction is initiated with ionomer glass (Secondary reaction)
- primary reaction isaddition polymerisation reaction
What are advantages of compomers?
Superior aesthetics to GPAC
Fluoride released
What are disadvantages of compomers?
System takes in oral fluids risk of staining
When is strength higher ?
with materials of high addition polymerisation reaction occurring
What are advantages of composites?
- Good strength & good aesthetics
- Command set ability
What are disadvantages of composites?
- Poor bonding to tooth tissue
- No fluoride release
When are fissure sealants used?
seal vulnerable fissures on occlusal surfaces of posterior teeth and prevent ingress of microbes
IS FS similar to composite?
no filler is present FS more flowable
What is FS unable to do?
bond directly to enamel and requires etch
An advantage of GPAC?
doesn’t require etch
Why are FS pigmented?
pigmented (for aesthetics) or clear for clinician to monitor caries formation underneath
What source of fluoride can be used under FS?
3M ESPE incorporated TBATFB
