Composite 1

Question 1

What clinical cases can direct filling materials be applied in?

Answer 1

• new dental caries
• abrasion / erosion
• failed restoration/secondary caries
• trauma

Question 2

What are the components of composite resin?

Answer 2

1. Filler particles
2. Resin
3. Camphorquinone
4. Low weight dimethacrylates
5. Silane coupling agent

Question 3

What are the types of filler particles?

Answer 3

types of glass

– microfine silica
– quartz
– borosilicate glass
– lithium aluminium silicate
– barium aluminium silicate

Question 4

What are the types of resin?

Answer 4

Monomers used:-
– BIS-GMA - reaction product of bisphenol-A and glycidyl methacrylate
– urethane dimethacrylates

Question 5

What are the key characteristics of resin monomers?

Answer 5

• bifunctional molecule
  (C=C bonds – facilitate crosslinking)
  – undergoes free radical addition polymerisation

Question 6

What are properties of camphorquinone and why is it added?

Answer 6

– activated by blue light
– produces radical molecules
– these initiate free radical addition polymerisation of BIS-GMA
– leading to changes in resin properties
(ie increased molecular weight, so increased viscosity, and strength)

Question 7

Why are low weight dimethacrylates (e.g TEDGDMA) added?

Answer 7

added to adjust viscosity & reactivity

Question 8

Why is a silane coupling agent added?

Answer 8

– normally water will adhere to glass filler particles, preventing resin from bonding to the glass surface
– a coupling agent is used to preferentially bond to glass and also bond to resin

Question 9

What are the classifications of composite?

Answer 9

• Curing method
  – light cured
• self cured
• Filler type:
  – microfilled
• submicron hybrid
• heavily filled
• Handling characteristics
  – condensable
  – syringeable
  – flowable

Question 10

What are the 3 steps of composite development?

Answer 10

• filler particles
• curing (activation)
• particle /resin bonding

Question 11

What is the advantageous effect of adding filler particles?

Answer 11

• improved mechanical properties
  – strength, rigidity, hardness, abrasion resistance etc
• lower thermal expansion (still not perfect)
• lower polymerisation shrinkage (still a problem)
• less heat of polymerisation (BUT not negligible)
• improved aesthetics
• some radiopaque

Question 12

What are the ways composite can be cured?

Answer 12

• self curing (two pastes)
• Light curing (blue light 440nm, one paste)

Question 13

How is composite actived in the curing process of self curing and light curing?

Answer 13

self curing = benzoyl peroxide + aromatic tertiary amine

light curing = camphorquinone + blue light

=

free radicals are formed (polymerisation)

Question 14

What are the two lights used for light curing?

Answer 14

halogen
LED

Question 15

What are the advantages of a light curing system?

Answer 15

• extended working time
  – on-demand set, triggered when light activated
• less finishing
• immediate finishing
• less waste
• higher filler levels (not mixing two pastes)
• less porosity (not mixing two pastes)

Question 16

What layer of composite sets best/first in light curing?

Answer 16

Most of blue light is absorbed close to the surface.

Composite resin nearest the surface sets the most readily and becomes hard.

Question 17

What is used to signify the depth of cure? (system)

Answer 17

• Surface hardness profile is accepted as more realistic
• Instrumentation used to create indentations on surface, that are quantified
• And then sub-surface measurements related to this
• DoC is defined as depth at which material HARDNESS is about 80% that of the cured surface

Question 18

What is the depth of cure and what is it used to assess?

Answer 18

Depth of cure
– the depth to which the composite resin polymerises sufficiently

it’s HARDNESS is about 80% (to 90%) of the cured surface (D = 0mm)

typically 2mm

indicates increment thickness to use when building a restoration

using increment > 2mm results in UNDER-POLYMERISED base “soggy bottom” poor bonding to tooth….early failure !

Question 19

What layer thickness should be used for hybrid composites?

Answer 19

2mm

Question 20

What are bulk fill composites?

why are they used

Answer 20

Has lucerin initiator as well as camphorquinone

UV and blue light needed to polymerise (cure) material fully

produce a deeper DOC resulting in less time wasted

Question 21

What layer thickness is recommended for bulk fill composites?

Answer 21

4-6mm

Question 22

What are the problems that can occur with light curing?

Answer 22

• light / material mismatch - overexpose
• premature polymerisation from dental lights - avoid exposure
• optimistic “depth of cure” values (small increments)
• recommended setting times too short
• polymerisation shrinkage

Question 23

What are the safety concerns for light curing?

Answer 23

thermal trauma from heat generation (exothermic reaction)
ocular damage from intense light sources,