Composite 3 Flashcards
What does a one paste system?
no mixing required
2 one paste systems for composites
- syringe and bottle systems
- capsules
Explain syringe and bottle systems
- transfer to cavity using spatula
- dispense onto mixing pad
- don’t take straight from bottle - cross infection risk
Advantages and disadvantages of capsules
- pre-measured dose size and easy to transfer
- more waste
4 steps of free radical addition polymerisation
- activation
- initiation
- propagation
- termination
Explain propagation
- monomer converts to polymer, chains crosslink
- mechanical/physical properties related to molecular weight
- proceeds for as long as possible
3 steps of termination
- viscosity increases too high to allow radicals and monomers to meet
- two radicals meeting - cancel each other out
- impurity atoms react with radicals (oxygen can react easily but oxygen radicals much less reactive)
What is the oxygen inhibition layer?
- often called air inhibition
- prematurely terminated polymer
- weak, soft layer - easily damaged
- potentially leads to composite restoration failing
Explain matrix strip
- typically a thin polymer film
- provides barrier between composite and atmosphere during polymerisation
- reduces oxygen inhibition must be used carefully
A freshly polymerised surface is … and …
smooth and glossy
How does polishing and finishing happen?
- polished to adapt margins
- use a range of products with different particle sizes and abrasive types
- glaze applied
Traditional vs modern glaze technique
- trad is not filled, like acrylic resin so had poor abrasion resistance
- modern some are filled for better abrasion resistance
Process of choosing aesthetics of composite
- initial shade matching by shade and polish/gloss
- time constraints - accurate matching is time constraining
- requirements for location (posterior vs anterior)
How does staining affect aesthetics?
- dietary considerations
- solvents like alcohol, mouthwashes
- dietary factors like coffee, wine, turmeric
- whitening agents
How do CQ influence long term colour?
yellowing over time
How does roughening affect long term stability?
- abrasion from food and oral hygeine
- matrix removed
- lose gloss
How does marginal staining affect aesthetics over time?
- polymerisation shrinkage pulls away from margin
- microleakage
- amount of shrinkage related to adhesion strength
Chemical activation patterns
- shrinkage is uniform within filling
Light activation patterns of shrinkage
- non-uniform within filling
- shrinkage tends to be towards light
- relevant to adhesion - different stress depending on cavity
Magnitude of shrinkage depends on …
- degree of conversion
- monomer molecular weight
- filler concentration
- strength of adhesion to tooth tissue
- configuration factor termed C-factor
How does degree of conversion affect polymerisation shrinkage?
- monomers take up more volume than polymer
- greater conversion the greater the contraction
How does monomer molecular weight affect polymerisation shrinkage?
- greater monomer mass lower shrinkage
How does filler concentration affect polymerisation shrinkage?
- more filler leads to lower shrinkage
How does strength of adhesion to tooth tissue affect polymerisation shrinkage?
- composites don’t bond to enamel or dentine
- need an adhesive
The more surfaces composite bonded to, …
- shrinkage will have more effect
- shrinkage affects different cavities classes differently
C factor =
ratio of bonded surfaces to free surfaces
High C factor indicates …
shrinkage is a problem
What is meant by
- C factor 0
- C factor 0.2
- C factor 0.5
- no bonded surfaces
- one bonded surface
- two bonded surfaces
Failure composite restorations is due to …
- posterior restorations
(secondary caries, wear, fracture) - 1-5% anterior restorations
Failure depends on what factors?
- number of restored walls (C factor)
- composite volume (size of cavity)
- endodontic treatment
- correct use of composite by clinician
Properties of light activated composites depend on degree of conversion. How?
- requires good illumination
- make sure light guides are clean from contamination
- greater conversion near surface - use matrix strip to reduce air inhibition
- limited depth of cure
Polymerisation is a exo/endothermic reaction
Explain
- exothermic
- temp rise is proportional to volume
- larger cavities = larger temp rise
- light unit will contribute to heat
Light activated composites are available in what varieties?
- microfilled
- hybrid
- universal
- bulk fill
- packable
Composites vs amalgam in appearance
- composites tooth coloured
- patients prefer ‘invisible’ restorations
- tooth matching only at time of placement
Compare biocompatibility of composite and amalgam
- mercury in amalgam is public health issue
- no evidence it poses a health risk to people
- composites contain BisGMA with BPA, concerns of estrogenicity
- all monomers and amines are cytotoxic
- polishing comp leads to aerosols of silica - can cause pneumo-silicosis
Cavity design of composite vs amalgam
- undercuts required for amalgam
- amalgam weak in thin sections - angle at interface with enamel important
- composite adhesively attached to enamel and dentine - can be conservative
Composite vs amalgam for cavity sealing
- bonding of composite to enamel and dentine reduces marginal leakage
- depends on successful bonding and magnitude of polymerisation shrinkage
- amalgams not normally bonded - corrosion products
Compare durability of composite and amalgam
- hardness, stregnth and toughness are similar as composite is improving
- amalgam slightly more so as thick sections
