Rest: Materials

Question 1

COMPOSITE

What are the five components of composite ?

Answer 1

• Glass filler particles i.e. alumina, silica, borosilicate.
• Resin i.e. BisGMA.
• Photoinitiator i.e. camphorquinoine.
• Silane coupling agent.
• Low weight dimethacrylates i.e. TEGDMA.
  *

Question 2

COMPOSITE

What is the benefits/disadvanatges of smaller filler particle size vs. large ?

Answer 2

• Small filler particles - better aesthetics, poorer mechanical properties.
• Large filler particles - better mechnical properties, likely to stain and poorer aesthetics.

Question 3

COMPOSITE

What is the function of resin ?

Answer 3

• Resin is involved in setting reaction.
• Long monomer chains with C=C.
• Undergoes activation by photoinitiator.
• Causes free radical polymerisation.
• Crosslinking occurs generating monomer growth.
• Which results in increased viscosity and mechnical properties.
• Hydrophobic end also bonds with DBA.

Question 4

COMPOSITE

What is the purpose of camphorquinoine ?

Answer 4

• Photoinitiator.
• Acivtated by blue light.
• Causes release of free radical which initiates free radical polymerisation of resin.
• Resulting in increased molecular weight, viscosity and mechnical properties.

Always some unreacted monomer - risk of leaching and pulp irritation.

Question 5

COMPOSITE

What is the purpose of silane coupling agent ?

Answer 5

• Removes moisture from the surface of glass particles which allows resin and glass particle bonding.
• Methoxy group hydrolyses hydroxy group.

Question 6

COMPOSITE

What is the purpose of low weight dimethacrylates ?

Answer 6

Changes viscosity and polymerisation rate.

Question 7

COMPOSITE

What is the standard depth of cure for composite ?

Answer 7

2mm.

Knoop Hardness Test (ISO 4049).

Question 8

COMPOSITE

What problems can arise which might affect light cure systems ?

Answer 8

• Premature setting due to dental light.
• Optimistic depth of cure (use increments - 2mm).
• Polymerisation shrinkage (risk of cuspal fracture and microleakage).

Question 9

COMPOSITE

List some benefical properties of enamel.

Answer 9

Aesthetics. Smooth surface. Biocompatible. Anticariogenic. Radiopaque. Low thermal diffusivity and conductivity. Similar mechnical properties to dentine.

Question 10

COMPOSITE

What is the biggest disadvantage with composite’s properties ?

Answer 10

• High thermal expansion coefficient.
• High polymerisation contraction.

Question 11

BONDING SYSTEMS - COMPOSITE TO ENAMEL/DENTINE

Bonding to enamel - what material is used ?

Answer 11

37% phosphoric acid.

Question 12

BONDING SYSTEMS - COMPOSITE TO ENAMEL/DENTINE

How does acid etch improve bonding to enamel ?

Answer 12

• Etch roughens long enamel prisms containing hydroxyapetite crystals - changing the structure to a ‘keyhole’ appearance.
• Etch also increases the surface energy of enamel by removing the smear layer and increases surface wettability.
• This allows micromechnical bonding of resin through interlocking.

Question 13

BONDING SYSTEMS - COMPOSITE TO ENAMEL/DENTINE

Explain why bonding to dentine is more difficult than bonding to enamel.

Answer 13

• Non-inert surface and continuously releases water which prevents flow of DBA into the dentinal tubules and results in low surface energy.
• There are also varying sizes/densities of dentinal tubules.
• Also has smear layer.

Question 14

BONDING SYSTEMS - COMPOSITE TO ENAMEL/DENTINE

What properties should dentine bonding agent have ?

Answer 14

• Low viscosity.
• Able to make intimate contact with dentine.
• Allow adhesion with resin.

Question 15

BONDING SYSTEMS - COMPOSITE TO ENAMEL/DENTINE

In what two ways does dentine bonding agent facilitate bonding between resin and tooth surface ?

Answer 15

• Allows for interlocking forming mechnical bond.
• Molecular entanglement occurs forming chemical bond.

Question 16

BONDING SYSTEMS - COMPOSITE TO ENAMEL/DENTINE

What are the three components of dentine bonding agent ?

Answer 16

• Dentine conditioner.
• Primer.
• Adhesive.
• Photoinitiator.

Question 17

BONDING SYSTEMS - COMPOSITE TO ENAMEL/DENTINE

What is the function of a dentine conditioner in DBA ?

Answer 17

Removal of smear layer.

Question 18

BONDING SYSTEMS - COMPOSITE TO ENAMEL/DENTINE

What is the purpose of primer (HEMA) in DBA ?

Answer 18

• Forms hydrophillic bond with dentine (hydroxyl group and collagen).
• Forms hydrophobic bond with resin (C=C).

Question 19

BONDING SYSTEMS - COMPOSITE TO ENAMEL/DENTINE

What is the purpose of adhesive (BisGMA or HEMA) in DBA ?

Answer 19

• Helps with micromechnical bond by infiltating tubules and encourages molecular entanglement.
• Forms hybrid layer by encorperating collagen and smear layer into bond.

Question 20

BONDING SYSTEMS - COMPOSITE TO ENAMEL/DENTINE

What is the difference between total etch vs. self etch ?

Answer 20

• Total etch - removes entire smear layer.
• Self etch - encorporates smear layer (organic materials) into bond, resulting in hybrid layer.

Question 21

CAVITY LINING MATERIALS

What is the aims of a cavity lining material ?

Answer 21

• Protection from thermal and chemical irritation.
• Protection from bacterial microleakage.
• Reduce inflammation and pain.

Question 22

CAVITY LINING MATERIALS

How thin should cavity lining material application be ?

Answer 22

0.5mm

Question 23

CAVITY LINING MATERIALS

What are the ideal properties of a cavity lining material ?

Answer 23

• Low thermal properties - prevent recurrent nerve stimulation.
• High mechnical properties - used under deep restorative materials.
• Provide good marginal seal - prevent microleakage.
• Be radiopaque - to see secondary caries formation.
• Cariostatic - prevent microleakage.

Question 24

CAVITY LINING MATERIALS

Name three different types of cavity lining materials.

Answer 24

• CaOH.
• ZOE or resin modified ZOE.
• Glass ionomer.

Question 25

# CAVITY LINING MATERIALS What is the setting reaction for CaOH lining material ?

Answer 25

* Chelation setting reaction. * Zinc oxide (base) and butylene glyco disilicate (catalyst).

Question 26

# CAVITY LINING MATERIALS What is the properties of CaOH lining material ?

Answer 26

* Bactericidal (pH12). * Pulpal irritant causing necrosis of odontoblasts & causing teritary dentine formation.

Question 27

# CAVITY LINING MATERIALS What are the disadvantages of CaOH lining material ?

Answer 27

* Low compressive strength. * Soluble and unstable. * Requires RMGI to be placed over the top.

Question 28

# CAVITY LINING MATERIALS What are the benefits of using RMGI as cavity lining material ?

Answer 28

* Bonds and seals dentine - prevents microleakage. * Resin filling materials can bond. * Low thermal conductivity & diffusivity. * Thermal expansion coeffient similar to dentine. * High compressive strength. * Provides good marginal seal. * Benzoyl idodines and bromides released as products from polymerisation reaction have bactericidal effects.

Question 29

# CAVITY LINING MATERIALS What is the main disadvantage of using RMGI as cavity liner ?

Answer 29

* Possibility of unreacted monomer (HEMA). * Cytotoxic and causes pulpal irritation.

Question 30

# CAVITY LINING MATERIALS When should CaOH (Dycal) and RMGI (Vitrebond) be used ?

Answer 30

* CaOH - direct or indirect pulp caps with RMGI over the top to prevent dissolution of CaOH. * RMGI on its own - on deep cavities under amalgam & composite restorations.

Question 31

# CAVITY LINING MATERIALS ZOE cavity lining can ONLY be used under what material ?

Answer 31

Amalgam - prevents resin setting in composites. ## Footnote But poor compressive strength - not used first choice for cavity lining. Can be used as temporary restorations, root canal sealant, PD dressings.