Composite 2

Question 1

What are qualities of conventional, microfine and hybrid?

Answer 1

• Conventional:
  – strong but problems with finishing and staining
• Microfine:
  – smaller particles - inferior mechanical properties but smooth
• Hybrid:
  – originally compromise between conventional &
  microfine
  – most modern composites are hybrids
• improved filler loading and coupling agents have led to improvement in mechanical properties

Question 2

What is the compressive strenght and young’s modulus of composite?

Answer 2

compressive stress of around 350 MPa
high Young’s modulus of around 15 GPa

Question 3

What is hardness?

Answer 3

Resistance to scratching material surface (indentation existence)

Question 4

What is abrasion?

Answer 4

Removal of surface layers when two surfaces make frictional contact

Question 5

What does surface roughness affect?

Answer 5

Appearance
Plaque retention
Sensation when in contact with tongue

Question 6

What component of composite is hard?

Answer 6

Filler particles

Question 7

What are material factors affecting wear?

Answer 7

• filler material
• particle size distribution
• filler loading
• resin formulation
• coupling agent

Question 8

What are clinical factors affecting wear?

Answer 8

• cavity size & design
• tooth position
• occlusion
• placement technique
• cure efficiency
• finishing methods

Question 9

What is a beneficial property of composite?

Answer 9

Bond to tooth/ compatible with bonding systems

Question 10

How does composite bond to enamel and denting?

Answer 10

• enamel - acid etch technique
• dentine - dentine / universal bonding systems

Question 11

What is the acid etch technique?

Answer 11

30% phosphoric acid for 20 secs on original enamel surface

Question 12

What is the typical bond strength in MPa dependent on surface preparation of tissue, composite brand and test method?

Answer 12

40 MPa

Question 13

What does a good bond cause?

Answer 13

• reduce microleakage
• counteract polymerisation shrinkage
• good bond will reduce likelihood of gap between restoration and tooth

Question 14

How should cavity design be for composite?

Answer 14

Minimise cavity design - no need for retention undercuts as the bond holds the restoration in place

Question 15

What is good bonding in relation to stress?

Answer 15

Good bonding - stress spreads over contact areas

restoration does not have to withstand full stress - stress transferred to tooth and bone

However poor bond to tooth concentrates stress at the interface so failure more likely

Question 16

What should the thermal conductivity of composite be?

Answer 16

of composite resin should be low to avoid pulpal damage from hot & cold foods/fluids - it is low

Question 17

What is thermal diffusivity and how should it be for composite?

Answer 17

• How readily a material transmits heat when exposed to a short/transient stimulus
• ideally it should be low – it’s similar to dentine

Question 18

What should the thermal expansion of composite be?

Answer 18

of composite resin should be equal to tooth, to reduce microleakage- BUT it’s high-which is poor

Question 19

What are properties of composite?

Answer 19

• Aesthetics - good, range of shades
• Radiopaque - some radiopaque (diagnose secondary caries)
• Handling / viscosity - variations in viscosity between products affects handling technique

Question 20

What are components of aesthetics?

Answer 20

• shade range
• translucency
• maintenance of properties over lifetime
• resistance to staining
• surface finish

Question 21

What are the handling/ viscosity components that should be considered?

Answer 21

• light curing
• viscosity
• should be “user friendly”
  – but not at expense of other properties

Question 22

What is the shrinkage of composite?

Answer 22

• low setting shrinkage
– polymerisation shrinkage still a problem
as stresses develop at hard tissue surfaces (making de-bonding more likely)
– bonding agents and clinical techniques help minimise impact of this

Question 23

What is the biocompatibility of composite?

Answer 23

– generally thought to be OK
– but increasing concern about resins in general (NB not all monomer is polymerised ! )

Question 24

When is RMGI used, when is compomer used and when is composite resin used?

Answer 24

Resin Modified GI
- high caries risk
- frequent attenders

Compomer
- caries under control
- regular attenders

Composite resin
- low caries risk patients