Lining Materials Flashcards
what is the purpose of a liner
thermal - protect pulp from temperature damage
chemical - protect pulp from chemicals released from restoration
bacteria - protect pulp from bacteria due to microleakage from restoration
what is the difference between a therapeutic liner and a palliative liner
therapeutic - put down to reduce inflammation of pulp, stops thermal conduction of restorative material, definitive restoration can be placed on top
palliative - put down in reversible pulpitis, causes pulp to regress and tertiary dentine is formed, temp restoration placed over, can then go back and do definitive restoration
give some examples of ideal properties of a liner material
low thermal conduction - reduce heat transferred to pulp to prevent pulpal injury
thermal expansion - should be similar to that of dentine and enamel, prevent micro leakage, 8 or 11
mechanical strength - needs to be high to withstand pressure of placing restorative material on top
low solubility - if soluble, dentinal fluid will cause it to wash away
why is a calcium hydroxide liner useful
creates an environment with a pH of 12, bacteria requires an acidic environment, therefore, kills any bacteria remaining. also irritates the dentine, causing odontoblasts to produce tertiary dentine, results mineralised layer between pulp and restoration
what is a disadvantage of calcium hydroxide
low mechanical strength, and highly soluble, any microleakage can result in the lining disappearing
what are the constituents of zinc phosphate liner and what is the reaction
zinc oxide and phosphoric acid, acid base reaction followed by a hydration reaction
what is a problem associated with zinc phosphate
has an initial low pH, can cause pulpal irritation, also an exothermic reaction and heat damages the pulp, doesnt bind to the tooth tissue, micro leakage is possible
what is the difference between zinc phosphate and zinc polycarboxylate
both use zinc oxide but different acids
what benefits does zinc polycarboxylate acid have
bonds to tooth in similar way to GIC, less heat released, has a low initial pH but returns to normal much faster
what are some disadvantages of zinc polycarboxylate
lower mechanical strength than zinc phosphate, high solubility, opaque
what is the reaction in zinc oxide eugenol
chelation reaction between zinc oxide and eugenol, produces zinc eugenolate mix, integrates unreacted zinc oxide into material
what are some properties of ZOE
low thermal conduction, soluble - bad as break down material but good as eugenol is released which calms down the pulp, low mechanical strength - cant be used under amalgam as wouldnt withstand packing
why can ZOE not be used under composite restorations
prevents the resin from setting
how is ZOE resin modified
addition of resin, doesnt interact with setting reaction just increases mechanical strength
what is added in EBA ZOE
ethoxybenzoic acid, quartz and alumina
