Cavity lining materials
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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