Composite

Question 1

Give the components of Composite Resin

Answer 1

• Glass filler particles
• Resin (BIS-GMA monomer)
• Camphorquinone
• Low weight dimethacrylates
• Silane coupling agent

Question 2

Give some glass filler particles examples

Answer 2

• Microfine silica
• quartz
• Lithium aluminum silicate

Question 3

What is BIS-GMA a reaction of ?

Answer 3

• Bisphenol-A and Glycidyl methacrylate

Question 4

What happens to the Resin monomer BIS-GMA?

Answer 4

• Contains C=C to facilate crosslinking
• Undergoes free radical addition polymerisation

Question 5

Give an example of low weight dimethacrylate and why are they used in composite resin?

Answer 5

• TEGDMA
• Added to adjust viscosity and polymerisation reactivity

Question 6

What does Camphorquinone do?

Answer 6

• Photoinitator (activate by blue light)
• Initiates free radical addition polymerization of BIS-GMA
• Increases viscosity and strength of resin

Question 7

Why are Silane coupling agents used in composite resins?

Answer 7

• Create good bond between glass filler particles and resin
• Bonds instead of water which is good

Question 8

What is the effect of adding glass particles?

Answer 8

• Improved mechanical properties (strength and rigodity and hardness)
• Lower thermal expansion
• Lower polymeristaion shrinkage
• Less heat of polymerisation
• Improved aesthetics

Question 9

How is composite activated in self curing composite resins?

Answer 9

• Benzoyl peroxide + aromatic tertiary amine
• Forms free radicals to break resin C=C bonds
• Induces free radical addition polymerisation

Question 10

How is composite activated in light curing composite resins?

Answer 10

• Photoinitiator camphorquinone + blue light (430-490nm)
• Induces free radical addition polymeristaion

Question 11

What is the definition of Depth of Cure? Why does is it apply to composite resin?

Answer 11

• Depth at which material Hardness is about 80% that of cured surface
• Indicates increment thickness of 2mm of less when building restoration
• Increments >2mm results in under polymerised base (soggy base)

Question 12

Why can you use Bulk Fill composites up to 6mm increments?

Answer 12

• Has Lucerin intitiator as well as Camphorquinone
• Has diff optical absorption spectrum so need UV and blue light to polymerise material

Question 13

What are some potential problems from light curing?

Answer 13

• Premature polymerisation from dental lights
• Polymerisation shrinkage (affects bond to tooth - potential for cuspal fracture and microleakage)

Question 14

What thermal properties does composite posess?

Answer 14

• Low thermal conductivity (low to avoid pulpal damage)
• Low thermal diffusivity (sim to dentine)
• High thermal expansion coefficient (not good as this increases risk of microleakage of saliva or bacterial ingress)

Question 15

What type of patients would you give composite, compomer and RMGI to?

Answer 15

Composite resins - low caries risk
Compomer - Med caries risk
RMGI - High caries risk

Question 16

What properties makes composite ideal for usage?

Answer 16

good aesthetics

good handling qualities

light or self cure

anti-cariogenic (some claim to release fluoride)

radiopaque

biocompatible (not all monomer polymerised though)

polishable

Question 17

Pros and cons to light cure

Answer 17

cure on demand
extended working time
less waste

premature polymerisation from dental light
polymerisation shrinkage (affects bond to tooth - potential for cuspal fracture and microleakage)
depth of cure
light and material mismatch

Question 18

How is Flowable comp different to conventional comp?

Answer 18

flowable composite has much smaller and less filler particles, hence increased viscosity however it is weaker.

viscosity allows it to adapt to base of cavity