endodontic materials

Question 1

categories of endo materials

Answer 1

Instruments
Irrigants
Intra-canal medicaments
Obturation materials
Sealers
Pulp Capping materials
Root-end filling materials

Question 2

endo instruments

Answer 2

Mechanical phase of chemomechanical disinfection

Metal files used to remove soft and hard tissues
Removes micro-organisms
Creates spaces for disinfectants/medicaments
Creates appropriate shape for obturation

Question 3

physical properties of endo materials

Answer 3

Stress - tensile/compressive/shear

Stress concentration point - abrupt changes in the geo shape that leads to higher stress in that point

Strain = response to stress = how much deformation undergoes

Elastic limit = maximal strain that when applied to file, allows file to return to original dimensions

Elastic deformation = reversible deformation that does not exceed elastic limit

Shape memory

Plastic deformation

Plastic limit

Question 4

cyclic fatigue

Answer 4

Freely rotating in a curvature
Generation of tension/compression cycles
Cyclic fatigue
Failure

Question 5

endo instrument fracture causes

Answer 5

• Training and proficiency in the NiTi system of choice
• Create a manual glide path
• Employ a crown-down instrumentation technique to ensure straight-line access
• Use an electric speed and torque controlled motor
• NiTi files should be used in constant motion using gentle pressure
• Avoid triggering or disable the autoreverse mode
• Use of rotary files in abruptly curved or dilacerated canals should be avoided

Question 6

stainless steel hand files

Answer 6

Alloy of iron, carbon and chromium
Nickel may also be present
Improved carbon steel – rusting
13-26% chromium prevents rusting
Passivation layer of chromium oxide

work hardening = strengthening by deformation
dislocations interact and create obstructions in crystal lattice
resistance to dislocation formation develops

Question 7

nitinol

Answer 7

Equiatomic alloy of nickel and titanium
Exotic metal – does not conform to typical rules of mettalurgy
Super-elasticity – application of stress does not result in usual proportional strain

Temperature-dependent structures martensite and austenite
Crystal lattice structure altered by temperature or stress

Question 8

shape memory

Answer 8

shape memory alloys are materials that can be deformed at one temperature but when heated or cooled, return to their original shape.

Question 9

components of an endo rotary instrument

Answer 9

Taper – diameter change along working surface
Flute – groove to collect dentine and soft tissue
Leading/Cutting edge – forms and 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 10

irrigant role in endo treatment

Answer 10

Facilitate removal of debris
Lubrication
Dissolution of organic and inorganic matter
Penetration to canal periphery
Kill bacteria/yeasts/viruses
Biofilm disruption
Biological compatibility
Does not weaken tooth structure

Question 11

sodium hypochlorite (NaOCl)

Answer 11

NaOCl ionises in water into NA+ and the hypochlorite ion, OCl-
Establishes equilibrium with hypochlorous acid (HOCl)
Acid/Neutral HOCl predominates
pH 9 and above OCl- predominates
HOCl is responsible for antibacterial activity
Effect on organic material
Inability to remove smear layer by itself
Possible effect on dentine properties

Question 12

factors important for NaOCl function

Answer 12

concentration
volume
contact
mechanical agitation
exchange

Question 13

removal of smear layer

Answer 13

17% EDTA
10% Citric Acid
MTAD (Mixture of a Tetracycline isomer, an Acid, and a Detergent
Sonic and Ultrasonic irrigation

Watch apical control!

Question 14

irritant interactions

Answer 14

Interaction with NaOCl forms para-chloroaniline
Cytotoxic and carcinogenic
Uncertain bioavailability

Question 15

properties of an ideal obturation material

Answer 15

Easily manipulated with ample working time
Dimensionally by tissue fluids stable
Seals the canal laterally and apically
Non-irritatant
Impervious to moisture
Unaffected by tissue fluids
Inhibits bacterial growth
Radiopaque
Does not discolour tooth
Sterile
Easily removed if necessary

Question 16

gp

Answer 16

Natural rubber and gutta percha are polymers of same monomer - isoprene
Trans isomer of polyisoprene
Exists in two crystalline forms alpha and beta
Alpha phase is the naturally occurring form
Alpha phase heated above 65C melts into amorphous phase
Cooled slowly returns to alpha phase
Cooled rapidly recrystalises as beta phase
Beta phase used in commercially prepared dental gutta-percha

Question 17

gp cones

Answer 17

20% Gutta-percha
65% Zinc Oxide
10% Radiopacifiers
5% Plasticizers
Standardised, non-standardised and size-matched

Question 18

sealer function

Answer 18

Seals space between dentinal wall and core
Fills voids and irregularities in canal, lateral canals and between gutta-percha points used in lateral condensation
Lubricates during obturation

Question 19

properties on an ideal sealer

Answer 19

Exhibits tackiness to provide good adhesion
Establishes a hermetic seal
Radiopacity
Easily mixed
No shrinkage on setting
Non-staining
Bacteriostatic or does not encourage growth
Slow set
Insoluble in tissue fluids
Tissue tolerant
Soluble on retreatment

Question 20

zinc oxide and eugenol

Answer 20

Mixing vehicle mostly eugenol
Finely sifted zinc oxide to enhance flow
Radio-opacity < gutta-percha
Can be modified with germicides
Rosin or Canada Balsam to increased dentine adhesion
Corticosteroids
Zinc Oxide effective antimicrobial and may afford cytoprotection
Resin acids 90% component of Rosins affect lipids in cell membrane thus strongly antimicrobial/cytotoxic
Although toxic, may overall be beneficial with longlasting antimicrobial effect combined with cytoprotective effects
Setting is a chemical process combined with physical embedding of zinc oxide in a matrix of zinc eugenolate
Eugenolate formation constitutes hardening – CaOH accelerates this process so must be removed from canals
Free eugenol which remains can act as an irritant
Lose volume with time due to dissolution – resins can modify this

Question 21

GI sealers

Answer 21

advocate due to dentine bonding properties
Removal upon retreatment is difficult
Minimal antimicrobial activity

Question 22

resin sealers

Answer 22

Long history of use – development of AH26
Epoxy Resin
Paste-Paste mixing
Slow setting - 8 hours
Good sealing ability
Good flow
Initial toxicity declining after 24 hours

Epiphany – dual cure dental resin composite sealer – used with Resilon
BisGMA
Ethoxylated BisGMA
Urethane-dimethacrylate UDMA
Hydrophilic difunctional methacrylates
Fillers of calcium hydroxide, barium sulphate, barium glass and silica
Requires self-etch primer

EndoRez is a UDMA resin-based sealer
Hydrophilic
Good penetration into tubules
Biocompatible
Good radio-opacity

Question 23

calcium silicate sealers

Answer 23

High pH (12.8) during the initial 24 hours of the setting
Hydrophilic
Enhanced biocompatibility
Does not shrink on setting
Non-resorbable
Excellent sealing ability
Quick set - three to four hours – requires moisture
Easy to use

Question 24

medicated sealers

Answer 24

Sealers containing paraformaldehyde not acceptable
Lead and mercury components removed
Severe and permanent toxic effects on periradicular tissues
Sargenti paste, Endomethasone, SPAD

Question 25

what happens when conditions change?

Answer 25

pulp cap
pulpotomy and pulp regeneration
lateral perforation repair
apicoectomy
furcation perforation repair
root resorption repair
apexification

Question 26

mineral trioxide aggregate

Answer 26

grey =
Earliest formulations
Less toxic than Portland cement
Better setting characteristics
Tooth discolouration

Tricalcium silicate
Dicalcium silicate
Tricalcium Aluminate
Tetracalcium aluminoferrite
Bismuth oxide

white =
Smaller particle size
Reduced discolouration

Tricalcium silicate
Dicalcium silicate
Calcium aluminate
Bismuth oxide
Calcium sulphate dehydrated

Question 27

setting reaction

Answer 27

Hydraulic cements
Composed of several phases
When mixed with water a chemical reaction occurs between these phases and water (Hydration)

White and grey MTA undergo different setting reactions

Extended setting times
Modifications to change characteristics

Question 28

the ideal root filling

Answer 28

Various endodontic materials have been used
Generally a core material and sealer
Always sealer used to create a fluid-tight seal
AAE states NSRCT “involves the use of biologically acceptable chemical and mechanical treatment of the root canal system to promote healing and repair of the periradicular tissues”