CSA clinical aspects of resin composite Flashcards
Properties of resin composite?
tooth coloured
• strong
• hard wearing
• Relatively easy to place
What are the liquid components of composite?
- Bis-GMA
- TEGDMA
- Yellow solution has foil as when light exposed sets hard
What are the solid components of composite?
• Silica Filler >stirred into mixture >forms mouldable paste
What is the chemistry of resin composite?
- Resin matrix = where polymerisation occurs
* Filler particles bond to resin matrix via silane coupling agent
What do filler particles do?
reduce shrinkage and make substance harder
What are the negatives of composite?
- Polymerisation shrinkage
- Technique sensitive
- Highly affected by moisture
- Doesn’t bond to tooth Needs a bonding agent
What is polymerisation shrinkage?
• Monomers form a clinical bond to each other when set
space between them reduced as occurs
what helps in reducing shrinkage?
BisGMA and Filler particles
What does shrinkage cause?
gaps - prone to microleakage , plaque go in and recurrent caries
- sensitivity too since air reach
Why is moisture control needed for composite ?
hydrophobic
cotton wool rubber dam needed
good gingiva health so less bleeding
What happens when there’s areas where moisture control can’t be achieved ?
subgingival restoration
How to place composite?
- Cavity prep by drilling out caries
- Etch area (enamel & dentine for 15 s) > wash off acid for least 15 s
- Dry,don’t over dry ( for 5 seconds)
- Apply bond > this is what composite bonds to
- Light cure for 10-20 seconds
What does etching cause enamel to do?
- etch goes down prisms in enamel and opens up gap
- incr. SA and more retentive
what happens when bond applied?
micro mechanical retention
What is bonding agent?
unfilled resin, flowable and enter pores made into enamel
What does composite chemically adhere to ?
layer of bonding agent
What is cavity modification for composite?
- must bevel edges of cavity > with bur at 45-degree angle to tooth
- so etch & bond make more contact with more enamel prisms
What does cavity modification for composite ensure?
o Avoids unsupported enamel
o Presents ends of enamel prisms for etching
o Provides larger SA to bond to
o Helps blend colour of restoration with rest of tooth
what does etching beyond margins of cavity ensure
Helps in blending the restoration with the tooth
What is process for bonding to dentine?
etching > priming >Bonding
why is harder to cause retention to dentine?
it is wet , mix of collagen fibres and HAP
What dissolves dentine smear layer?
Acid and mineral content of dentine
What does priming do, adding HEMA bifunctional monomer solvent ?
has end sticks to composite & end sticks to organic materials > attract collagen fibres
•Primer pushes water out way
don’t overdry when priming?
collagen fibres fall
then apply composite and light cure
