Plastic Restorations - Compomers Flashcards
What are Compomers?
Developed to combine advantages of fluoride release with resin composites - RESIN COMP WHICH EXHIBITED A SUSTAINED AND EFFECTIVE RELEASE OF FLUORIDE
- Primarily a resin system with an additional (difunctional) resin is incorporated
What’s the generic name of Compomer?
Polyacid-modified resin composite
- Describes their composition and by implication their setting mechanism
What are the Resin constituents of Compomer?
Contains 2 monomeric components:
- Dimethacrylate (urethane dimethacrylate)
- Difunctional resin monomer containing both carboxyl and methacrylate groups
What’s Difunctional Resin Monomer
TCB resin = reaction product of butane tetracarboxylic acid and hydroxyethylmethacrylate
- cross-linking agent in a primary reaction
- Source of carboxyl groups for 2nd reaction with glass
Hydrophilic monomers - enhances water diffusion within resin matrix
- Hydrophobic and Hydrophilic ends
What are the other constituents of Compomer?
Filler:
- Fluoro-alumino-silicate glass (glass ionomer cement)
- Imparts strength
- Source of fluoride ions for use in 2nd reaction
- Forms a salt matrix with carboxylate groups
- Filler loading volume of between 42 & 67%
- Contain lithium to convey radiopacity
Photo-activators & Initiators:
- Camphorquinone
- Tertiary amine
What’s the setting reaction for Compomer?
2 stages - primarily a polymerisation reaction which is complete on exposure to curing light energy
Stage 1:
- Initial setting reaction is initiated by light
- Free radical polymerisation reaction
- Cross-linking of the end groups on the UDMA and Methacrylate groups to form a resin polymer matrix which the glass is trapped
(Difunctional monomer binds to dentine)
Stage 2:
- 2nd reaction occurs between the glass and carboxylate groups of the difunctional resin
- Requires restoration to be bathed in saliva
- Water is taken up by the resin system
- Hydrogen ions dissolve the outer surface of glass and release the fluoride ions
- Polysalt matrix is formed around the glass as fluoride is release
- Acid/base reaction that is aided by additions of small percentages of hydrophilic resin to the resin mi to encourage diffusion of water within the resin and fluoride out of it – diffusion takes several weeks
What are the mechanical properties of Compomer?
Compared to resin comp, it has lower:
- Compressive strengths
- Flexural strengths
- Elastic moduli
- Not useful for higher stress situations
What are the physical properties of Compomer?
- Displays polymerisation shrinkage due to resin - OCCURS IMMEDIATELY ON LIGHT CURING
- Can disrupt any bonding that is being formed
- Compensate for poly shrinkage should be same as resin comp
Should an intermediate bonding system be used for Compomer?
- YES
- Needed to achieve adhesion to too tissue
- Little or no adhesion achieved as a result of 2ndary setting reaction
- No chelation reaction unless the carboxylate groups are in close prox to the tooth surface
Do you etch with Compomers?
- Don.t need to etch
- Recommended though by some manufacturers as no acid etching results in reduced bond strength - so etch to maximise adhesion
How if fluoride released?
- Fluoride release is inferior to Conventional GIC
- Dependent on secondary setting reaction which occurs after placement
- Slow steady release with little fluoride burst seen initially
- Fluoride release is dependent on conc gradient between external environment and the restoration surface for diffusion of the fluoride ions
- Surface of restoration has a greater flu ion conc then the surroundings then migration of ions occurs
What determines the concentration of fluoride viable for release in Compomer?
- Rate of secondary reaction of the glass with the pendant carboxyl groups - determined by their proximity to the reactive glass surface
What’s the influence of water sorption within Compomer?
Typically water sorption adversely affects most hydrophobic resin systems
- Addition of hydrophilic resin can facilitate uptake of water and this material cannot fully set until water sorption has occurred and the secondary glass filler/carboxyl reaction has been completed
- Saturation occurs within a week of placement in the mouth
What is a potential drawback and benefit of water sorption?
Drawback:
- Uncontrolled reaction may lead to excessive expansion of the material with the risk of damage to the tooth
Benefit:
- Expansion may offset poly shrinkage
-
What are the other drawbacks of water sorption with Compomer?
Uptake of fluids leads to discolouration of restoration - relatively shortly after placement
