what materials are placed into cavities?
5
composite resin
glass ionomer
amalgam
precious metal
ceramic
what are the disadvantages of restoratives?
3
may not make immediate contact with the tooth surface - secondary caries
heat released during setting/curing can damage pulp
release of chemicals may irritate pulp
what do cavity lining materials do?
2
prevent gaps
act as a protective barrier
what are the differences between cavity bases and linings?
cavity base
* thick mix placed in bulk
* dentine replacement to minimise bulk of material or block out undercuts
cavity lining
* thin coating over exposed dentine
* dentine sealer to promote health of pulp
what is the purpose of a cavity liner?
3
- pulpal protection from chemical stimuli, thermal stimuli and bacteria and endotoxins
- therapeutic to reduce inflammationn within pulp
- palliative to reduce symptoms prior to definitive treatment
what are the properties of lining materials?
9
- ease of use
- thermal properties
- mechanical properties
- radiopaque
- marginal seal
- solubility
- cariostatic
- biocompatible
- compatible with restorative materials
how are lining materials easy to use?
3
easy to mix
long working time to allow easy placement
short setting time
what are the thermal properties of lining materials?
3
low thermal conductivity
similar thermal expansion coefficient to dentine
similar or lower thermal diffusity to dentine
what are the mechanical properties of lining materials?
2
high compressive strength
modulus similar to dentine
why should lining materials be radiopaque?
2
should be easy to see the difference between lining and tooth
easier to see of there are any leakages or secondary caries
why should the lining material be a marginal seal?
should form a chemical bond to dentine which is permanent and impermeable
how soluble should a lining material be?
low solubility
how is a lining material cariostatic?
3
releases fluoride
antibacterial
prevents secondary caries around restoration
how is the lining material biocompatible?
3
non-toxic
doesn’t damage pulp (ph neutral, no excess heat when setting)
low thermal conductivity
what types of materials can be bases or liners?
4
setting calcium hydroxide: liner
zinc oxide based cements: base
glass ionomer and resin modified glass ionomer: base or liner
palliative cements: base
what kind of reaction occurs with setting calcium hydroxide and what is the reaction between? what does it result in?
3
setting reaction is a chelation reaction
between ZnO (filler material) and butylene glycol disalicylate (reactive element)
results in a cement with an initia pH of around 12
how does setting calcium hydroxide work?
2
- kills cariogenic bacteria as creates a highly alkaline environment
- irritates the odontoblast layer to start making reparative tertiary dentine (calcified bridge forms at base - calcium comes from pulp)
what are the properties of setting calcium hydroxide?
5
quick setting time ✓
radiopaque ✓
easy to use ✓
low compressive strength ✖
unstable and soluble ✖
soluble=if cavity leaks then lining disappears-may be due to wet dentine
what are examples of zinc oxide based cements?
5
zinc phosphate
zino polycarboxylate
zinc oxide eugenol (ZOE)
resin modified ZOE
ethoxybenzoic acid (EBA) ZOE
what makes up the powder and liquid components of zinc phosphate cement?
powder
* zinc oxide
* magnesium dioxide
* alumina and silica oxides
liquid
* phosphoric acid (aq)
* oxides which are buffers - aluminum and zinc oxides
aluminium oxide - even consisteny, zinc oxide - slows reaction
what reaction occurs with zinc phosphate cement and what is the end product?
3
ZnO + 2H3PO4 -> Zn(H2PO4)2 + H2O (acid base reaction)
ZnO + Zn(H2PO4)2 + H2O -> Zn3(H2PO4)2.4H2O (hydration)
crystalised phosphate matrix produced
what are problems with the zinc phosphate cement?
7
- low initial pH around 2 = pulpal irritation
- exothermic setting reaction (gives off heat)
- not adhesive to tooth or restoration
- not cariostatic
- final set takes 24 hours
- brittle
- opaque
what are the advantages with zinc polycarboxylate cement?
4
- bonds to tooth surface
- less heat from reaction
- low initial pH but returns to neutral quickly
cheap
what are the disadvantages with zinc polycarboxylate cement?
5
- difficult to mix
- difficult to manipulate
- soluble in oral environment at lower pH
- opaque
- lower modulus and compressive strength than zinc phosphate
