Cavity lining materials

Question 1

purpose of cavity lining materials

Answer 1

• protects pulp from irritants and heat (transmission and exothermic setting)
• more intimate contact with tooth
• calm the pulp, protecting from bacterial endotoxins when used in prior temporary restoration and kept in for permanent

Question 2

ideal properties of cavity lining materials

Answer 2

• same thermal expansion, diffusivity and modulus as dentine
• low thermal conductivity
• long work time and quick setting on command
• chemical bond to dentine
• radiopaque
• cariostatic (F releasing or antibacterial)

Question 3

names of cavity lining materials

Answer 3

1. resin modified glass ionomer/glass ionomer
2. palliative cements (seldom)
3. setting calcium hydroxide
4. zinc oxide based cements

Question 4

what is setting calcium hydroxide and why good/bad

Answer 4

• two pastes, base (calcium hydroxide) and catalyst
• chelation reaction with pH of 12

benefits

 - alkaline so anti acid secreting bacteria
 - tertiary dentine seals off moist dentine as this paste necrotic to odontoblast processes
 - quick setting and easy use
 - radiopaque

negatives

 - low compressive strength
 - unstable and soluble (will dissolve if leakage or water from dentine)

Question 5

types of zinc oxide cements and insight into properties

Answer 5

i. zinc phosphate
- acid (phosphoric acid) - base (zinc oxide), powder liquid reaction
good:
- cheap and easy
bad:
- early pH = 2 and exothermic setting can damage pulp
- nonadhesive to tooth or restoration, opaque, brittle, set takes 24hrs and non cariostatic

ii. zinc polycarboxylate
- same as above but polyacrylic acid instead
- means can bond to tooth surfaces
- however more difficult to use and lower modulus and compressive strength

iii. zinc oxide eugenol (ZOE)
- used for under amalgam, root canal sealers (slow 24hr setting) and periodontal dressing (fast 5min setting)
- same reaction except eugenol acid instead
good:
- radiopaque, good work and setting time, low thermal conductivity
bad:
- released eugenol inhibits resin setting (cant use with composite)
- high solubility and low strength

iv. resin modified ZOE
- same as ZOE but resin added = not involved in reaction, increased compressive strength and decreased solubility
- used for temporary restorations

v. ethoxybenzoic acid ZOE (EBA ZOE)
- same as ZOE except this acid used and quartz and aluminia added