Cavity lining materials Flashcards
purpose of cavity lining materials
- 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
ideal properties of cavity lining materials
- 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)
names of cavity lining materials
- resin modified glass ionomer/glass ionomer
- palliative cements (seldom)
- setting calcium hydroxide
- zinc oxide based cements
what is setting calcium hydroxide and why good/bad
- 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)
types of zinc oxide cements and insight into properties
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