Endodontic Materials

Question 1

work hardening

Answer 1

strengthening of a metal by plastic deformation
- crystal structure dislocation
- dislocations interact & create obstructions in crystal lattice
- resistance to dislocation formation develops
- observed as work hardening

Question 2

martensite v austenite

Answer 2

crystal lattice structure altered by temp / stress
character & proportions determine mechanical properties of metal
martensite = soft & ductile, easily deformed
austenite = strong & hard

Question 3

components of endodontic rotary instrument

Answer 3

taper - diameter change along working surface
flute - groove to collect dentine & soft tissue
leading / cutting edge - forms & deflects dentine chips
land - surface extending between flutes
relief - reduction in surface of land
helix angle - angle cutting axis forms with long axis of file

Question 4

irrigant properties

Answer 4

• facilitate removal of debris
• lubrication
• dissolution of organic & inorganic matter
• penetration to canal periphery
• kill bacteria / yeast / viruses
• biofilm disruption
• biological compatibility
• does not weaken tooth structure

Question 5

sodium hypochlorite NaOCl

Answer 5

ionises in water into Na+ & OCl- (hypochlorite ion)
HOCl then formed is responsible for antibacterial activity

Question 6

effect of NaOCl

Answer 6

effect on organic material
inability to remove smear layer by itself
possible effect on dentine properties

Question 7

factors important for NaOCl function

Answer 7

1. concentration
2. volume
3. contact
4. mechanical agitation
5. exchange

Question 8

what happens during canal prep for obturation

Answer 8

smear layer formed during prep
this is organic pulpal material & inorganic dentinal debris
superficial 1-5um with packing into tubules
includes bacterial contamination, substrate & interferes with disinfection
prevents sealer penetration

Question 9

options for removal of smear layer

Answer 9

1. 17% EDTA
2. 10% citric acid
3. MTAD
4. sonic & ultrasonic irrigation

Question 10

properties of an ideal obturation material

Answer 10

easily manipulated with ample working time
dimensionally stable with tissue fluids
seals canal laterally & apically
non irritant
impervious to moisture
unaffected to tissue fluids
inhibits bacterial growth
radiopaque
does not discolour tooth
sterile
easily removed (if necessary)

Question 11

GP used in dentistry

Answer 11

beta form
naturally occurring is alpha form but when heated above 65o and cooled rapidly is recrystallises as beta form

Question 12

GP cones

Answer 12

20% GP
65% zinc oxide
10% radiopacifiers
5% plasticisers

Question 13

sealer functions

Answer 13

seals space between dentinal wall & core
fills voids & irregularities in canal, lateral canals and in between GP points used in lateral condensation
lubricates during obturation

Question 14

properties of an ideal sealer

Answer 14

• exhibits tackiness to provide good adhesion
• establishes a hermetic seal
• radiopacity
• easily mixed
• no shrinkage on setting
• non staining
• bacteriostatic
• slow set
• insoluble in tissue fluids
• tissue tolerant
• soluble on retreatment

Question 15

zinc oxide eugenol as sealer

Answer 15

free eugenol remains & can act as an irritant
loses volume with time due to dissolution (resins can modify this)

Question 16

glass ionomer sealers

Answer 16

advocated due to dentine bonding properties
removal upon re tx is difficult
minimal antimicrobial activity
little clinical data to support use

Question 17

resin sealers

Answer 17

AH +
epoxy resin with paste - paste mixing
slow setting ~ 8hrs
good sealing ability
good flow
initial toxicity declining after 24hrs

Question 18

MTA white

Answer 18

this is a bioceramic cement
smaller particle size than MTA grey and has reduced tooth discolouration
e.g. tri / dicalcium silicate, calcium aluminate