cavity lining materials

Question 1

functions

Answer 1

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

Question 2

base

Answer 2

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

Question 3

lining

Answer 3

thin coating <0.5mm

over exposed dentine

Question 4

materials

Answer 4

setting CaOH - liner
ZnO cements: base
GI/RMGIC
(palliative cements - base)

Question 5

guidelines

Answer 5

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

Question 6

ideal properties

Answer 6

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

Question 7

thermal conductivity

Answer 7

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

Question 8

TEC

Answer 8

change in length per unit length for a temp rise of 1 degree

ppm degree celsius -1

Question 9

thermal diffusivity

Answer 9

similar to conductivity

cm2/sec

Question 10

setting CaOH liner chemistry

Answer 10

2 pastes e.g. life, decal
base
catalyst

Question 11

setting CaOH liner base

Answer 11

CaOH 50% active ingredient
ZnO 10% filler
Zn stearate <1% filler
plasticiser

Question 12

setting CaOH liner catalyst

Answer 12

butylene glycol disalicylate 40% reactive ingredient
TiO2 filler
CaSO4 filler
Ca tungstate filler and radiopaquer

Question 13

setting CaOH liner setting reaction

Answer 13

acid base
chelation reaction between ZnO and butylene glycol disalicylate
= cement with initial pH 12

Question 14

setting CaOH liner mode of action

Answer 14

bactericidal to cariogenic bacteria
- alkaline env
irritant - reparative tertiary dentine formation
- irritation and necrosis to odontoblast layer
- pulp shrinks away
- calcified bridge - from pulp

Question 15

setting CaOH liner advantages

Answer 15

quick setting time
radiopaque
easy to use

Question 16

setting CaOH liner disadvantages

Answer 16

low compressive strength = v soft so can’t put amalgam on top
unstable and soluble - dissolves away v easily even with just moist dentine

Question 17

ZnO based cements

Answer 17

zinc phosphate
zinc polycarboxylate
ZOE
resin modified ZOE
ethoxybenzoic acid (EBA) ZOE

Question 18

which ZnO based cements arent really used nowadays?

Answer 18

zinc phosphate

zinc polycarboxylate

Question 19

ZOE cements uses

Answer 19

linings/base in deep cavities
 - under amalgam Rxs
temporary Rxs
RC sealer - slow setting 24hrs
PD dressings - fast setting 5mins

Question 20

zinc phosphate cement advantages

Answer 20

lasts for a v long time in cavities
easy to use
cheap

Question 21

zinc phosphate cement constituents - powder

Answer 21

ZnO >90%
MgO2 <10% - white colour, increases compressive strength
other oxides (Al and Si) - improve physical properties and alter shade

Question 22

zinc phosphate cement constituents - liquid

Answer 22

H3PO4 50%

oxides to buffer - Al, Zn

Question 23

zinc phosphate cement reaction

Answer 23

initially acid base
then hydration - form a crystallised phosphate matrix
maturation - binds water from setting reaction - stronger, less porous

Question 24

zinc phosphate cement problems

Answer 24

low initial pH2
exothermic setting reaction
not adhesive to tooth or Rx
not cariostatic
final set takes 24hrs
brittle
opaque

Question 25

zinc polycarboxylate cement chemistry

Answer 25

phosphoric acid replaced by poly acrylic acid

Question 26

zinc polycarboxylate cement advantages

Answer 26

bonds to tooth
less heat of reaction
pH returns to neutral more quickly and longer chain acids don’t penetrate dentine as easily
cheap

Question 27

zinc polycarboxylate cement disadvantages

Answer 27

difficult to mix and manipulate
soluble in oral env at lower pH
opaque
lower modulus and compressive strength than ZnPO4

Question 28

RMZOE

Answer 28

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

Question 29

ZOE cement chemistry

Answer 29

acid base reaction
ZnO + Eugenol (acid) - zinc oxide eugenolate
setting - chelation reaction, matrix bonds the unreacted ZnO particles

Question 30

advantages of ZOE cement

Answer 30

working and setting time
low thermal conductivity
radiopaque

Question 31

disadvantages of ZOE cement

Answer 31

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

Question 32

EBA ZOE cement chemistry

Answer 32

powder: ZnO, quartz/alumina, hydrogenated rosin
liquid: eugenol, EBA

Question 33

EBA ZOE cement setting

Answer 33

as with ZOE but EBA ‘encourages crystalline structure which imparts greater strength to set material’

Question 34

EBA ZOE cement properties

Answer 34

stronger than ZOE/RMZOE

less soluble

Question 35

(RM) GI lining

Answer 35

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