cavity lining materials Flashcards
functions
prevent gaps - microleakage
protective barrier - pulpal protection
- chemical stimuli - unreacted chemicals in filling material or initial pH
- thermal stimuli - exothermic setting reaction or heat conduction
therapeutic - calm inflammation in pulp
palliative
- reduce symptoms before definitive tx. reversible pulpitis
base
thick mix placed in bulk
dentine replacement used to minimise the bulk of the material or to block out undercuts
more common in metal Rxs
lining
thin coating <0.5mm
over exposed dentine
materials
setting CaOH - liner
ZnO cements: base
GI/RMGIC
(palliative cements - base)
guidelines
for cavities in dentine
- consider RMGIC for amalgam and for larger composite cavities
only use CaOH when cavity approaches pulp
- either as a direct or indirect pulp cap over deepest part of cavity
cover CaOH with RMGIC before final Rx
ideal properties
ease of use - easy to mix - long working time - short setting time high compressive strength modulus similar to D radiopaque - distinguish between lining and tooth - see leakage/secondary caries marginal seal - form chemical bond to dentine - permanent and impenetrable low solubility cariostatic biocompatible - pH neutral low thermal conductivity TEC should match tooth thermal diffusivity as low as tooth or lower
thermal conductivity
how well heat energy is transferred through a material
heat flow through a cylinder of unit CS area and unit length, with a temp difference of 1 degree between the ends
W/m-1/degrees Celsius -1
TEC
change in length per unit length for a temp rise of 1 degree
ppm degree celsius -1
thermal diffusivity
similar to conductivity
cm2/sec
setting CaOH liner chemistry
2 pastes e.g. life, decal
base
catalyst
setting CaOH liner base
CaOH 50% active ingredient
ZnO 10% filler
Zn stearate <1% filler
plasticiser
setting CaOH liner catalyst
butylene glycol disalicylate 40% reactive ingredient
TiO2 filler
CaSO4 filler
Ca tungstate filler and radiopaquer
setting CaOH liner setting reaction
acid base
chelation reaction between ZnO and butylene glycol disalicylate
= cement with initial pH 12
setting CaOH liner mode of action
bactericidal to cariogenic bacteria
- alkaline env
irritant - reparative tertiary dentine formation
- irritation and necrosis to odontoblast layer
- pulp shrinks away
- calcified bridge - from pulp
setting CaOH liner advantages
quick setting time
radiopaque
easy to use
setting CaOH liner disadvantages
low compressive strength = v soft so can’t put amalgam on top
unstable and soluble - dissolves away v easily even with just moist dentine
ZnO based cements
zinc phosphate zinc polycarboxylate ZOE resin modified ZOE ethoxybenzoic acid (EBA) ZOE
which ZnO based cements arent really used nowadays?
zinc phosphate
zinc polycarboxylate
ZOE cements uses
linings/base in deep cavities - under amalgam Rxs temporary Rxs RC sealer - slow setting 24hrs PD dressings - fast setting 5mins
zinc phosphate cement advantages
lasts for a v long time in cavities
easy to use
cheap
zinc phosphate cement constituents - powder
ZnO >90%
MgO2 <10% - white colour, increases compressive strength
other oxides (Al and Si) - improve physical properties and alter shade
zinc phosphate cement constituents - liquid
H3PO4 50%
oxides to buffer - Al, Zn
zinc phosphate cement reaction
initially acid base
then hydration - form a crystallised phosphate matrix
maturation - binds water from setting reaction - stronger, less porous
zinc phosphate cement problems
low initial pH2 exothermic setting reaction not adhesive to tooth or Rx not cariostatic final set takes 24hrs brittle opaque
zinc polycarboxylate cement chemistry
phosphoric acid replaced by poly acrylic acid
zinc polycarboxylate cement advantages
bonds to tooth
less heat of reaction
pH returns to neutral more quickly and longer chain acids don’t penetrate dentine as easily
cheap
zinc polycarboxylate cement disadvantages
difficult to mix and manipulate
soluble in oral env at lower pH
opaque
lower modulus and compressive strength than ZnPO4
RMZOE
resins added to powder and liquid
don’t take part in reaction but give a stronger backbone to the set material
increased compressive strength - lining
reduced solubliity
ZOE cement chemistry
acid base reaction
ZnO + Eugenol (acid) - zinc oxide eugenolate
setting - chelation reaction, matrix bonds the unreacted ZnO particles
advantages of ZOE cement
working and setting time
low thermal conductivity
radiopaque
disadvantages of ZOE cement
low strength (weak H bonds) - not strong enough below amalgam - packing pressure would damage it high solubility - Eugenol constantly released released Eugenol inhibits set of resin based filling materials. softens them and can cause discolouration - don't use under composite
EBA ZOE cement chemistry
powder: ZnO, quartz/alumina, hydrogenated rosin
liquid: eugenol, EBA
EBA ZOE cement setting
as with ZOE but EBA ‘encourages crystalline structure which imparts greater strength to set material’
EBA ZOE cement properties
stronger than ZOE/RMZOE
less soluble
(RM) GI lining
bond to dentine and composite 2 paste 'clicker' system good thermal properties good compressive strength radiopaque generally light cured can predictably seal dentinal tubules - reduces micro leakage and helps prevent post-tx sensitivity not too soluble
