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)
