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BDS3 DMS > Endodontic Materials > Flashcards

Endodontic Materials Flashcards

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
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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
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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

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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

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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
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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.
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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
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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
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9
Q

Describe the 2 ways in which endodontic files can be manufactured

A
  1. Twisting
    • machined stainless steel wire
    • wire has square or triangular cross section
    • wire is twisted
    • work hardening occurs
  2. Cutting
    • machine stainless steel wire into desired shape
    • work hardening occurs
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10
Q

Is work hardening desirable in endodontic files?

A

Yes, it improves the physical properties

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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
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12
Q

What is nitinol?

A

equiatomic alloy of nickel and titanium

  • exotic metal which does not conform to the typical rules of metallurgy
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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

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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
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15
Q

What are the two crystal structures of NiTi

A

Martensite
- soft
- ductile
- easily deformed

Austenite
- strong
- hard

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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)

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17
Q

What are the components of an endodontic rotary instrument?

A
  • taper
  • flute
  • leading/cutting edge
  • land
  • relief
  • helix angle
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18
Q

What is the taper of an endodontic file?

A

the diameter change along the working surface

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19
Q

What is the flute of an endodontic file?

A

the groove to collect dentine and soft tissues

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20
Q

What is the leading/cutting edge of an endodontic file?

A

the edge which forms and deflects dentine chips

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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

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22
Q

What is the relief of an endodontic file?

A

the reduction in surface of land
- reduces friction

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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

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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

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25
Q

What are the functions of irrigants?

A
  • 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
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26
Q

What is the primary irritant used in endodontic treatment?

A

sodium hypochlorite (NaOCl)

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27
Q

Describe the structure and behaviour of sodium hypochlorite (NaOCl)

A
  • 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
Q

Describe the function of sodium hypochlorite (NaOCl)

A
  • 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
Q

What factors determine successful function of NaOCl?

A
  • concentration
  • volume
  • contact with tissue
  • mechanical agitation
  • exchange
30
Q

How is the smear layer formed and what challenges does it pose?

A
  • 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
Q

How is the smear layer removed

A
  • 17% EDTA
  • 10% citric acid
  • MTAD (Mixture of Tetracycline isomer, Acid and Detergent)
  • sonic and ultrasonic irrigation (activates irritant, increases efficacy)
32
Q

What must be considered careful when removing the smear layer?

A
  • apical control
33
Q

Why must irritants not be mixed?

A

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
Q

What is 0.2% chlorhexidine used for?

A
  • checking dam integrity
35
Q

Why would 2% chlorhexidine be used?

A
  • check for iatrogenic damage
  • sodium hypochlorite contraindicated
36
Q

What are the desired propertied of an obturation material?

A
  • 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
Q

What is the most common obturation material?

A

gutta-percha

38
Q

What is gutta-percha made from?

A

sap of trees from the sapodilla family

39
Q

What is the structure of gutta-percha?

A
  • trans isomer of polyisoprene
40
Q

Describe the two forms of gutta-percha

A

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
Q

What is the composition of gutta-percha cones?

A
  • 20% gutta-percha
  • 65% zinc oxide
  • 10% radiopacifiers
  • 5% plasticisers
42
Q

What are the different formats in which gutta-percha is available?

A
  • standardised
  • non-standardised
  • size matched
  • thermal obturation (carrier-base system)
  • injectable pellets
43
Q

In what ways can gutta-percha be modified to improve its characteristics?

A
  • coatings can be added
  • material impregnated
  • improve antimicrobial activity
  • improve interactions with sealers
  • improved handling (bi-ceramic nanoparticles)
44
Q

What are the functions of sealers?

A
  • 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
Q

What are the ideal properties of a sealer?

A
  • 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
Q

What are the components of zinc oxide and eugenol?

A
  • eugenol (mixing vehicle)
  • finely sifted zinc oxide (enhances flow)
  • may be modified with germicides
  • rosin or canada balsam
  • corticosteroids
47
Q

What are the properties of zinc oxide and eugenol?

A
  • 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
Q

Describe the setting process of zinc oxide and eugenol

A
  • 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
Q

What are the disadvantages of zinc oxide and eugenol as a sealer?

A
  • 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
Q

What are the advantages and disadvantages of glass ionomer sealers?

A

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
Q

Give examples of resin sealers

A
  • AH Plus
  • Epiphany + Resilon
  • EndoRez
52
Q

Describe AH Plus

A
  • endodontic sealer
  • contains epoxy resin
  • paste-paste mixing
  • slow setting (8 hours)
  • good sealing ability
  • good flow
  • rapid decline in toxicity (24 hours)
53
Q

Describe Epiphany + Resilon

A

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
Q

Describe EndoRez

A
  • resin endodontic sealer
  • hydrophilic
  • good penetration into dentine tubules
  • biocompatible
  • good radiopacity
55
Q

Describe Calcium Silicate Sealers

A
  • 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
Q

Describe medicated sealers

A

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
Q

What is mineral trioxide aggregate?

A
  • pulp capping/root end filling material
58
Q

What is the difference between grey and white mineral trioxide aggregate?

A

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
Q

What is the mineral trioxide aggregate setting reaction?

A
  • 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
Q

What can mineral trioxide aggregate be used for?

A
  • apical areas
  • perforation

good where moisture can be drawn upon by surrounding tissues

61
Q

What can mineral trioxide aggregate not be used for?

A

restorations in the oral cavity

  • material will be washed away before it sets
62
Q

What is biodentine?

A
  • bioceramic cement (modified MTA)
63
Q

How is biodentine used?

A
  • direct pulp capping
  • building up restorations (cut back and restored with composite)
64
Q

What are the advantageous properties of biodentine?

A
  • sets rapidly (within minutes)
  • can be used in anterior teeth (reduced staining)
65
Q

What is the tissue response to MTA?

A
  • where MTA is placed osteogenesis is induced
  • osteogenesis related to pH change
  • hydroxyapatite formed on surface
  • cementum forms directly on MTA plug
66
Q

Who can use orthograde MTA?

A

only hight specialised practitioners should use this
- used instead of GP
- very difficult to manipulate and remove

BDS3 DMS (10 decks)

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