cavity lining materials Flashcards
what is the most widely used lining material?
glass ionomer
why is glass ionomer a good lining material?
it can bond and seal dentine
it can bond to the composite on top
it releases fluoride over time and can be cariostatic
why is glass ionomer easy to use?
mixing is simple two paste
light cured so command set
long working time short setting time
what is GIC thermal conductivity and diffusivity lower than?
dentine
how is thermal expansion in GIC compared to dentine?
similar
what is the compressive strength of GI lining materials?
> 170MPa
what are the benefits of glass ionomer linings?
radiopaque
marginal seal best as there is a chemical bond to enamel and dentine
only material to predictable seal dentinal tubules
-reduced microleakage & post op sensitivity
compare GIC to RMGIC
GIC greater solubility
GIC less soluble than other liners except zinc phosphate cement
RMGIC less soluble than any other cement
what are the disadvantages of glass inonomers?
fluoride release possible & cariostatic
benzoyl iodides and bromides released during polymerisation reaction
-cytotoxic and can be effective against residual cavity bacterial
complete cure required as unreacted HEMA may damage pulp
what lining material require etching but no surface tx?
glass ionomer
when is RMGIC used?
for cavities in dentine for amalgam and larger composite cavities
when is calcium hydroxide used?
only when cavity approaches pulp
what should calcium hydroxide be covered with?
RMGIC
-protects and prevents dissolution beneath rest.
what are the base constituents of Ca OH liner?
calcium hydroxide 50%
zonc oxide 10%
zinc stearate
N-ethyl toluene sulphonamine 40%
what are the catalyst constituents of Ca OH?
butylene glycol disaliclate
titanium dioxide
ca sulphate
ca tungstate
what is the setting reaction of a Ca OH liner?
chelation reaction between ZnO and butylene glycol disalicylate
what is the initial pH of Ca OH?
12
how is CaOH bactericidal to cariogenic bacteria?
highly alkaline liner kills bugs
how does CaOH irritation lead to reparative dentine formation?
cement causes irritation to odontoblast layer, causes necrosis -> tertiary dentine -> calcified bridge walling base of cavity from pulp
what are the properties of CaOH liners?
quick setting time radiopaque easy to use low compressive strength unstable soluble
what are the zinc oxide based cements?
zinc phosphate zinc polycarboxylate zinc oxide eugenol resin modified ZOE ethoxybenzoic acid ZOE
describe zinc phosphate cement
acid base reaction powder & liquid excellent clinical service easy to use cheap
what are the powders in zinc phosphate cement?
zinc oxide 90% magnesium dioxide -colour -compressive strength other oxides -improved physical properties
what are the liquids in zinc phosphate cement?
aqueous solution of phosphoric acid
oxides which buffer the solution
-aluminium oxide
-zinc oxide
what are the 2 reactions of zinc phosphate?
acid base
hydration
what are the problems with zinc phosphate cement?
initial pH 2 exothermic setting reaction not adhesive not cariostatic final set takes 24 hrs brittle opaque
describe the setting of zinc phosphate
aluminium oxide prevents crystalisation leading to amorphous glassy matrix of acid salt surrounding unreacted ZnO powder
matrix almost insoluble, porous contains free water from setting reaction
cement subsequently matures binding water leading to strong, less porous material
what is zinc polycarboxylate cement?
similar to zinc phosphate but phosphoric acid replaced by polyacrylic acid
what are the advantages of zinc polycarboxylate cement?
bonds to tooth surfaces like glass ionomer
less reaction heat
pH low to begin but becomes neutral faster
cheap
what are the disadvantages of zinc polycarboxylate cement?
difficult to mix difficult to manipulate soluble in oral environment at lower pH opaque lower modulus and compressive strength than zinc phosphate
what are the uses of ZOE and related materials?
linings in deep cavities -under amalgam temporary restorations root canal sealer periodontal dressings
what is the reaction of ZOE?
acid base
base is ZnO
acid is eugenol
describe the setting reaction of ZOE
chelation reaction of zinc oxide with eugenol to form zinc eugenolate matrix
matric bonds unreacted ZnO particles
what are the properties of ZOE?
adequate working time relatively rapid setting time low thermal conductivity low strength (20MPA) radiopaque
what are the consequences of ZOE high solubility?
eugenol constantly released
eugenol replaced by water -> disintegration of the material
eugenol when liberated has obtundant effect on pulp and can reduce pain
why should ZOE materials not be used under composite resin materials?
eugenol inhibits set of resin based materials
-softens and can cause discoloration
describe resin modified ZOE
resins added to powder and liquid -PMMA -polystrene in kalzinol do not take part on reaction but give a stronger backbone to set material increases compressive strength (40MPa) decreases solubility
what are the powder components of EBA cement?
ZnO 65%
quarts/alumina 35%
hydrogenated rosin 6%
what are the liquid components of EBA cement?
eugenol 37%
ethoxybenzoic acid EBA 63%
describe EBA setting
as with ZOE but EBA
-encourages crystalline structure which imparts greater strength to the set material
what are the properties of EBA?
stronger that ZOE/resin modified ZOE (60MPa)
less soluble
why are lining materials needed?
restoratives:
- may not make intimate contact w/ tooth surface
- heat released during setting/curing
- release of chemicals
- pulpal irritant
what is the function of lining material?
prevents gaps
acts as a protective barrier
what is a cavity base?
thick mix placed in bulk
dentine replacement used to minimise bulk of material or block out undercuts
more common in metal rest.
what is a cavity lining?
thin coating over exposed dentine
what does a liner protect the pulp from?
chemical stimuli from unreacted chemicals in filling material
thermal stimuli eg exothermic setting
bacterial and endotoxins eg microleakage
what is the therapeutic purpose of a liner?
to calm down inflammation w/i pulp and promote pulpal healing
what is the palliative purpose of a liner?
to reduce px syptoms prior to definitive tx carried out
-common in reversible pulpitis
what are the properties of lining materials
ease of use thermal properties mechanical properties radiopaque marginal seal solubility cariostatic biocompatible compatible with rest material
what is ease of use?
easy to mix
long working time
setting time short
-ideally command set
what are thermal properties?
thermal conductivity should be low
thermal expansion coefficient should be similar to dentine
thermal diffusivity should be similar to dentine or lower
what is thermal conductivity?
how well heat energy is transferred through a material
what is thermal expansion coefficient?
change in length per unit length for a temp rise of 1 degree
ideally liner should match tooth
what is thermal diffusivity
similar to conductivity
ideally as low as tooth
what are mechanical properties?
high compressive strength
-allow placement w/o brealomg
modulus similar to dentine
describe radiopaque
should be easy to see dif between lining and tooth
-easier to see if there is any leakage/secondary caries
describe marginal seal
ideally lining should form a chemical bond to dentine
bond should be permanent and impenetrable
what should solubility be?
low
what is cariostatic?
fluoride releasing
antibacterial
prevents secondary caries
what is biocompatibility?
non-toxic not damaging to pulp -pH -excessive heat low thermal conductivity
