Plastic Restorations - Compomers Flashcards Preview

Semester II - Dental Materials > Plastic Restorations - Compomers > Flashcards

Flashcards in Plastic Restorations - Compomers Deck (19)
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1

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

2

What's the generic name of Compomer?

Polyacid-modified resin composite

- Describes their composition and by implication their setting mechanism

3

What are the Resin constituents of Compomer?

Contains 2 monomeric components:

1. Dimethacrylate (urethane dimethacrylate)

2. Difunctional resin monomer containing both carboxyl and methacrylate groups

4

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

5

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

6

What's the setting reaction for Compomer?

2 stages - primarily a polymerisation reaction which is complete on exposure to curing light energy

Stage 1:
1. Initial setting reaction is initiated by light
2. Free radical polymerisation reaction
3. 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

7

What are the mechanical properties of Compomer?

Compared to resin comp, it has lower:

1. Compressive strengths
2. Flexural strengths
3. Elastic moduli

- Not useful for higher stress situations

8

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

9

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

10

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

11

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

12

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

13

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

14

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

-

15

What are the other drawbacks of water sorption with Compomer?

Uptake of fluids leads to discolouration of restoration - relatively shortly after placement

16

How resistance to wear is Compomer?

Poor resistance - wear observed quite quickly after placement

17

What are the indications for Compomer?

Class III cavities - strong enough and aesthetically acceptable (I woudn't recommend though)

Class V cavities - flexible matrix so able to retain in abfraction lesion

Restoration of deciduous teeth - bonds to tooth tissue

18

What are the contraindications for Compomer?

Where aesthetics is important - composite is better doesn't stain like compomer

Core build-ups - not strong enough as water uptake is needed to fully cure material

Class I, II, IV cavities - material not strong enough

Inter-visit restoration of endodontic access cavities - poor ability to seal as demonstrated by microleakage studies

19

Summary

- Relatively limited area of application

- Sticky in nature so handling can be difficult