Endodontic Materials Flashcards
What are the different categories of endodontic materials?
- instruments
- irrigants
- intra-canal medicaments
- obturation materials
- sealers
- pulp capping materials
- root-end filling materials
What are the functions of endodontic instruments?
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
What area of a stress-strain curve should endodontic files be kept in?
the elastic region
- does not exceed the elastic limit
- reduced the risk of fracture
What happens if an endodontic file passes the plastic limit?
instrument separation
- strain experienced by the instrument was too great
- fracture point of the instrument reached
- instrument failure
- challenging clinically
What is the relevance of torsional fatigue in relation to endodontic files?
- 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
What practice must be used with NiTi files to prevent instrument fracture?
- 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.
What different classifications of endodontic instruments exist?
- 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
Describe the components of stainless steel used for endodontic files
- 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
Describe the 2 ways in which endodontic files can be manufactured
- 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
Is work hardening desirable in endodontic files?
Yes, it improves the physical properties
Describe the process of work hardening
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
What is nitinol?
equiatomic alloy of nickel and titanium
- exotic metal which does not conform to the typical rules of metallurgy
What property of nitinol is different to that of most metals?
Super-elasticity
- application of stress does not result in usual proportional strain
Describe the crystal structure of NiTi
- temperature dependent structures, altered crystal lattice
- character and proportions determine the mechanical properties of the metal
What are the two crystal structures of NiTi
Martensite
- soft
- ductile
- easily deformed
Austenite
- strong
- hard
What instrument uses the two crystal structures of NiTi?
XP shaper files
- malleable and relaxed shape in martensitic phase
- robust shape in austenitic phase (when heated)
What are the components of an endodontic rotary instrument?
- taper
- flute
- leading/cutting edge
- land
- relief
- helix angle
What is the taper of an endodontic file?
the diameter change along the working surface
What is the flute of an endodontic file?
the groove to collect dentine and soft tissues
What is the leading/cutting edge of an endodontic file?
the edge which forms and deflects dentine chips
What is the land of an endodontic file?
the surface extending between flutes
- touches the wall of the canal
- develops considerable friction
What is the relief of an endodontic file?
the reduction in surface of land
- reduces friction
What is the helix angle of an endodontic file?
the angle the cutting axis forms with the long axis of the file
What is the function of shaped files?
the expanded form sweeps the wall of the root canal to more effectively debride the root surface
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
What is the primary irritant used in endodontic treatment?
sodium hypochlorite (NaOCl)
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
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
What factors determine successful function of NaOCl?
- concentration
- volume
- contact with tissue
- mechanical agitation
- exchange
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
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)
What must be considered careful when removing the smear layer?
- apical control
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
What is 0.2% chlorhexidine used for?
- checking dam integrity
Why would 2% chlorhexidine be used?
- check for iatrogenic damage
- sodium hypochlorite contraindicated
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
What is the most common obturation material?
gutta-percha
What is gutta-percha made from?
sap of trees from the sapodilla family
What is the structure of gutta-percha?
- trans isomer of polyisoprene
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
What is the composition of gutta-percha cones?
- 20% gutta-percha
- 65% zinc oxide
- 10% radiopacifiers
- 5% plasticisers
What are the different formats in which gutta-percha is available?
- standardised
- non-standardised
- size matched
- thermal obturation (carrier-base system)
- injectable pellets
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)
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
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
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
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
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)
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
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
Give examples of resin sealers
- AH Plus
- Epiphany + Resilon
- EndoRez
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)
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
Describe EndoRez
- resin endodontic sealer
- hydrophilic
- good penetration into dentine tubules
- biocompatible
- good radiopacity
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
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
What is mineral trioxide aggregate?
- pulp capping/root end filling material
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
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)
What can mineral trioxide aggregate be used for?
- apical areas
- perforation
good where moisture can be drawn upon by surrounding tissues
What can mineral trioxide aggregate not be used for?
restorations in the oral cavity
- material will be washed away before it sets
What is biodentine?
- bioceramic cement (modified MTA)
How is biodentine used?
- direct pulp capping
- building up restorations (cut back and restored with composite)
What are the advantageous properties of biodentine?
- sets rapidly (within minutes)
- can be used in anterior teeth (reduced staining)
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
Who can use orthograde MTA?
only hight specialised practitioners should use this
- used instead of GP
- very difficult to manipulate and remove
