1
Q
What are the different categories of endodontic materials?
A
- instruments
- irrigants
- intra-canal medicaments
- obturation materials
- sealers
- pulp capping materials
- root-end filling materials
2
Q
What are the functions of endodontic instruments?
A
the mechanical phase of chemo-mechanical disinfection
- removal of hard and soft tissues
- removal of microorganisms
- creation of space for disinfectants/medicaments
- creation of appropriate space for obturation
3
Q
What area of a stress-strain curve should endodontic files be kept in?
A
the elastic region
- does not exceed the elastic limit
- reduced the risk of fracture
4
Q
What happens if an endodontic file passes the plastic limit?
A
instrument separation
- strain experienced by the instrument was too great
- fracture point of the instrument reached
- instrument failure
- challenging clinically
5
Q
What is the relevance of torsional fatigue in relation to endodontic files?
A
- instrument binds to dentinal wall and is rotated
- bound portion does not rotate like driven portion
- increased rotation causes torque
- elastic limit is reached
- plastic deformation experienced resulting in failure
6
Q
What practice must be used with NiTi files to prevent instrument fracture?
A
- glide path must be created to reduce torsional fatigue
- straight line access in crown-down instrumentation technique to prevent instruments from working in a high stress form
- electric speed and torque controlled motors limit the torque applied to instruments
- rotation can be reversed if inappropriate torque is sensed but this point should not be reached
- rotary files in abruptly curved or dilacerated canals should be avoided.
- instruments should not be overloaded, use gently.
7
Q
What different classifications of endodontic instruments exist?
A
- manually operated (ISO No.3630-1)
- low speed instruments
- engine-driven NiTi rotary instruments
- engine driven instruments adapting to canal (XP shapers)
- engine driven reciprocating instruments
- ultrasonic instruments
8
Q
Describe the components of stainless steel used for endodontic files
A
- alloy of iron, carbon and chromium
- some contain nickel
- improved carbon steel to reduce rusting
- chromium (13-26%) prevents rusting
- passivation layer of chromium oxide prevents degradation
- rust resistance is less important in single use files
9
Q
Describe the 2 ways in which endodontic files can be manufactured
A
- Twisting
- machined stainless steel wire
- wire has square or triangular cross section
- wire is twisted
- work hardening occurs
- Cutting
- machine stainless steel wire into desired shape
- work hardening occurs
10
Q
Is work hardening desirable in endodontic files?
A
Yes, it improves the physical properties
11
Q
Describe the process of work hardening
A
strengthening of a metal by plastic deformation
- crystal lattice is regular in organisation
- crystal structure is dislocated when strain is applied to the point of plastic deformation
- dislocations create obstructions in the crystal lattice which create resistance to further dislocations
- increased hardness of material
12
Q
What is nitinol?
A
equiatomic alloy of nickel and titanium
- exotic metal which does not conform to the typical rules of metallurgy
13
Q
What property of nitinol is different to that of most metals?
A
Super-elasticity
- application of stress does not result in usual proportional strain
14
Q
Describe the crystal structure of NiTi
A
- temperature dependent structures, altered crystal lattice
- character and proportions determine the mechanical properties of the metal
15
Q
What are the two crystal structures of NiTi
A
Martensite
- soft
- ductile
- easily deformed
Austenite
- strong
- hard
16
Q
What instrument uses the two crystal structures of NiTi?
A
XP shaper files
- malleable and relaxed shape in martensitic phase
- robust shape in austenitic phase (when heated)
17
Q
What are the components of an endodontic rotary instrument?
A
- taper
- flute
- leading/cutting edge
- land
- relief
- helix angle
18
Q
What is the taper of an endodontic file?
A
the diameter change along the working surface
19
Q
What is the flute of an endodontic file?
A
the groove to collect dentine and soft tissues
20
Q
What is the leading/cutting edge of an endodontic file?
A
the edge which forms and deflects dentine chips
21
Q
What is the land of an endodontic file?
A
the surface extending between flutes
- touches the wall of the canal
- develops considerable friction
22
Q
What is the relief of an endodontic file?
A
the reduction in surface of land
- reduces friction
23
Q
What is the helix angle of an endodontic file?
A
the angle the cutting axis forms with the long axis of the file
24
Q
What is the function of shaped files?
A
the expanded form sweeps the wall of the root canal to more effectively debride the root surface
25
What are the functions of irrigants?
- facilitates removal of debris
- lubrication
- dissolution of organic and inorganic matter in root canal space
- penetration to canal periphery
- antimicrobial activity
- disruption of biofilm
- biological compatibility
- does not weaken tooth structure
26
What is the primary irritant used in endodontic treatment?
sodium hypochlorite (NaOCl)
27
Describe the structure and behaviour of sodium hypochlorite (NaOCl)
- NaOCl ionises in water into Na+ and OCl -
- equilibrium established with hypochlorous acid (HOCl)
- at pH 7 and below HOCl predominates
- at pH 9 and above OCl- predominates
28
Describe the function of sodium hypochlorite (NaOCl)
- has effect on organic material
- cannot remove the smear layer but can disrupt the organic component
- may have an effect of dentine properties
- HOCl is responsible for significant antimicrobial activity
29
What factors determine successful function of NaOCl?
- concentration
- volume
- contact with tissue
- mechanical agitation
- exchange
30
How is the smear layer formed and what challenges does it pose?
- formed during preparation
- composed of organic plural material and inorganic dentinal debris
- layer superficial at 1-5 micrometers depth with packing into tubules
- results in bacterial contamination
- interferes with disinfection
- prevents sealer penetration
31
How is the smear layer removed
- 17% EDTA
- 10% citric acid
- MTAD (Mixture of Tetracycline isomer, Acid and Detergent)
- sonic and ultrasonic irrigation (activates irritant, increases efficacy)
32
What must be considered careful when removing the smear layer?
- apical control
33
Why must irritants not be mixed?
precipitates can form
- sodium hypochlorite must be withdrawn
- EDTA can then be added
- sterile water may be used in between
parachloroaniline formed by NaOCl interactions
- cytotoxic
- carcinogenic
- uncertain bioavailability
34
What is 0.2% chlorhexidine used for?
- checking dam integrity
35
Why would 2% chlorhexidine be used?
- check for iatrogenic damage
- sodium hypochlorite contraindicated
36
What are the desired propertied of an obturation material?
- easily manipulated
- ample working time
- seals canal laterally and apically
- non-irritant
- impervious to moisture
- unaffected by tissue fluids
- inhibits bacterial growth
- radiopaque
- does not discolour tooth
- sterile
- easily removed if necessary
37
What is the most common obturation material?
gutta-percha
38
What is gutta-percha made from?
sap of trees from the sapodilla family
39
What is the structure of gutta-percha?
- trans isomer of polyisoprene
40
Describe the two forms of gutta-percha
Both are crystalline forms - alpha and beta
Alpha
- naturally occurring
- melts into amorphous phase at 65 degrees
- returns to alpha phase when cooled slowly
- recrystallises to beta phase when cooled rapidly
Beta
- commercially prepared dental gutta-percha
41
What is the composition of gutta-percha cones?
- 20% gutta-percha
- 65% zinc oxide
- 10% radiopacifiers
- 5% plasticisers
42
What are the different formats in which gutta-percha is available?
- standardised
- non-standardised
- size matched
- thermal obturation (carrier-base system)
- injectable pellets
43
In what ways can gutta-percha be modified to improve its characteristics?
- coatings can be added
- material impregnated
- improve antimicrobial activity
- improve interactions with sealers
- improved handling (bi-ceramic nanoparticles)
44
What are the functions of sealers?
- seal space between dentinal wall and core
- fill voids and irregularities in canal, lateral canals and GP points used in lateral condensation
- lubrication during obturation
45
What are the ideal properties of a sealer?
- tacky to provide good adhesion
- establish hermetic seal
- radiopaque
- easily mixed
- no shrinkage on setting
- non-staining
- bacteriostatic (ideally) or does not encourage growth
- slow set
- insoluble in tissue fluids
- tissue tolerant
- soluble on retreatment
46
What are the components of zinc oxide and eugenol?
- eugenol (mixing vehicle)
- finely sifted zinc oxide (enhances flow)
- may be modified with germicides
- rosin or canada balsam
- corticosteroids
47
What are the properties of zinc oxide and eugenol?
- less radiopaque than gutta-percha
- effective antimicrobial
- may provide cytoprotection
- dentine adhesion (rosin/canada balsam)
- resin acids in rosin affect lipids in the cell membrane so are antimicrobial/cytotoxic
- toxic in the early stages of setting
48
Describe the setting process of zinc oxide and eugenol
- chemical process combined with physical embedding of zinc oxide in matrix of zinc eugenolate
- eugenolate formation constitutes hardening (accelerated by CaOH so must be removed from canals)
49
What are the disadvantages of zinc oxide and eugenol as a sealer?
- free, unreacted eugenol can act as an irritant
- volume lost over time due to dissolution (apical seal especially diminished)
- dissolution evident on extrusion of previous treatments
- unstable long term
50
What are the advantages and disadvantages of glass ionomer sealers?
Advantages
- good dentine bonding properties
Disadvantages
- removal on pretreatment is difficult
- minimal antimicrobial activity
- little clinical data to support use
Not widely adopted in practice
51
Give examples of resin sealers
- AH Plus
- Epiphany + Resilon
- EndoRez
52
Describe AH Plus
- endodontic sealer
- contains epoxy resin
- paste-paste mixing
- slow setting (8 hours)
- good sealing ability
- good flow
- rapid decline in toxicity (24 hours)
53
Describe Epiphany + Resilon
dual cure resin composite endodontic sealer
Contains - BisGMA
- Ethoxylated BisGMA
- Urethane-dimethacrylate (UDMA)
- Hydrophilic difunctional methacrylate
- fillers (CaOh, BaSO4, Ba glass, silica)
- required self etch primer which is challenging to used in canals
54
Describe EndoRez
- resin endodontic sealer
- hydrophilic
- good penetration into dentine tubules
- biocompatible
- good radiopacity
55
Describe Calcium Silicate Sealers
- high pH
- pH 12.8
- initial 24 hours
- antimicrobial
- osteoinductive
- hydrophilic
- react well with moisture in dentinal tubules
- enhanced biocompatibility
- apical tissues found to react well adjacent
- no setting shrinkage
- non-resorbable
- excellent sealing ability
- quick setting
- 3-4 hours
- requires moisture
- easy to use
- increasingly used in practice
- expensive
- potentially challenging to retreat
56
Describe medicated sealers
NOT USED NOW
- sealers containing paraformaldehyde
- lead and mercury components have been removed
- severe, permanent toxic effects on periradicular tissue
- highly antimicrobial
- Sargenti paste, endomethasone, SPAD
57
What is mineral trioxide aggregate?
- pulp capping/root end filling material
58
What is the difference between grey and white mineral trioxide aggregate?
Grey
- earliest formulations
- results in tooth discolouration
- contains - tricalcium silicate
- dicalcium silicate
- tricalcium aluminate
- tertracalcium aluminoferrite
- bismuth oxide
White
- smaller particle size
- reduced discolouration
- contains - tricalcium silicate
- dicalcium silicate
- calcium aluminate
- dehydrated calcium sulphate
- bismuth oxide
59
What is the mineral trioxide aggregate setting reaction?
- several phases of hydraulic cement setting
- water is required for setting
- delayed setting reaction with a dormancy period in which the material remains unset
- delayed hardening until final set (many hours)
60
What can mineral trioxide aggregate be used for?
- apical areas
- perforation
good where moisture can be drawn upon by surrounding tissues
61
What can mineral trioxide aggregate not be used for?
restorations in the oral cavity
- material will be washed away before it sets
62
What is biodentine?
- bioceramic cement (modified MTA)
63
How is biodentine used?
- direct pulp capping
- building up restorations (cut back and restored with composite)
64
What are the advantageous properties of biodentine?
- sets rapidly (within minutes)
- can be used in anterior teeth (reduced staining)
65
What is the tissue response to MTA?
- where MTA is placed osteogenesis is induced
- osteogenesis related to pH change
- hydroxyapatite formed on surface
- cementum forms directly on MTA plug
66
Who can use orthograde MTA?
only hight specialised practitioners should use this
- used instead of GP
- very difficult to manipulate and remove
