Endodontic Materials Flashcards
What is the function of endodontic instruments
mechanical phase of chemomechanical disinfection
metal files used to remove soft and hard tissues
removes microorganisms
creates spaces for disinfectants/medicaments
creates appropriate shape for obturation
What are the important physical properties for endodontic instruments
stress stress concentration point strain elastic limit elastic deformation shape memory plastic deformation plastic limit
What is stress
deforming forecasters measured across a given area
can be shear/compressive/tensile/torsional
What are stress concentration points
abrupt changes in the geometric shape of a file that leads to a higher stress at that point
What is strain
response of a material to stress
amount of deformation a file undergoes during use
What is elastic limit
a set value representing the maximal strain that when applied to a file allows the file to return to original dimensions
in day to day use we try to keep it in the elastic region but sometimes we get to the plastic region when we see unwinding of files
What is elastic deformation
reversible deformation that does not exceed elastic limit
What is plastic deformation
permanent bond displacement occurring when elastic limit is exceeded
What is the plastic limit
the point at which a plastic deformed file breaks
What are the two types of failure for endo instruments
cyclic and torsional fatigue
What is cyclic fatigue
when the file is rotated in a curved canal, on one side it undergoes compressive force while the other undergoes tension force and because it is rotating we see the generation of tension/compression cycles resulting in work hardening, cyclic fatigue and eventually failure
What is torsional fatigue
when the instrument is in the canal it binds to the wall and is rotated but the bound portion doesn’t rotate like the driven portion of the instrument
This results in a torque making the instrument exceed the elastic phase, reach the elastic limit and undergo plastic deformation and then ultimate failure
What are ways we can prevent instruments fracture
training and proficiency in the NiTi system of choice
create a manual glide path
employ a crown down
instrument 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 disabling the autoreverse mode
use of rotary files in abruptly curved or dilacerated canals should be avoided
How can instruments be classified
manually operated
low speed instruments
engine driven nicke titanium rotary instruments
engine driven instruments that adapt to canal shape
engine driven reciprocating instruments
ultrasonic instruments
What is the alloy composition of stainless steel instruments
iron carbon chromium
may have nicke l
What is the function of chromium in the stainless steel
it creates a passivation layer of chromium oxide which prevents rusting
How are the stainless steel instruments created
they are made of machined stainless steel wire
they are square or triangular
they are twisted and this results in work hardening
it is machined into the desired shape and this results in work hardening also
What is work hardening
strengthening of a metal by plastic deformation
crystal structure dislocation
dislocations interact and create obstructions in crystal lattice
resistance to dislocation formation develops
What is nitinol
equiatomic alloy of nickel and titanium
What is special about nitinol
exotic metal and does not conform to typical rules of metallurgy
it displays super elasticity where the application of stress does not result in usual proportional strain
this is related to the forms that the NiTi can take e.g austenite and martensite
What is the crystal structure of NiTI
it can transition from austenite to marsenite based on temperate
this changes the mechanical properties of the metal
What are the mechanical properties of martensite
soft, ductile and easily deformed
What are the mechanical properties of austenite
quite strong and hard
used in production of endo materials
What is shape memory alloys
materials that can be deformed at one temp but when heated r cooled they return to their original shape
What is the benefit of NiTi in terms of its two phases
can be warmed up to change to A-phase and get a broader instrument that can occupy a larger space and so good for debridement
What are the components of an endodontic rotary instrument
taper flute leading/cutting edge land relief helix angle
What is a taper
diameter change along the working surface
What is the flute
groove to collect dentine and soft tissue
What is the leading/cutting edge
forms and deflect dentine chips
What is land
surface extending between flutes
What is relief
reduction in surface of land
this modifies the friction between instruments
What is the helix angle
angle cutting axis forms with long axis of file
this effects the nature of how the instrument works in the canal
Describe the wide radial land
provides blade support while adding peripheral strength to resist torsional and rotary stresses
What is the radial and relief
land is diminished in surface area so can reduce friction between the canal wall and instrument
What is the third radial land
stabilizes and keeps the instrument centre in the canal and minimizes over engagement
What is the positive rake angle
provides the active cutting action of the K3
What are the properties of irritants
facilitates removal of debrirs lubrication dissolution of organic and inorganic matter penetration to canal periphery kill bacteria/yeasts/viruses biofilm disruption biological comaptibility does not weaken tooth structure
How does sodium hypochlorite work
it ionizes in water into Na+ and hypochlorite ion
it establishes an equilibrium with hypochlorous acid
What condition does HOCl predominate in the equilibrium
acid / neutral
What condition does OCl- predominate in the equilibrium
ph 9
What is HOCl responsible for
antibacterial activity
What does sodium hypochlorite effect
organic material
unable to remove smear layer by itself (inorganic component)
possible effect on dentine properties
What are factors important for hypochlorite function
concentration volume contact mechanical agitation exchange
How is the smear layer formed
happens during prep
made of organic pulpal material and inorganic dentinal debris
superficial 1-5 micrometers with packing into tubules
made of bacterial contamination, substrate and interferes with disinfection
prevents sealer penetration
How is the smear layer removed
17% EDTA
10% citric acid
MTAD
sonic and ultrasonic irrigation
What should be known about EDTA
can’t use with hypochlorite
don’t want to create precipitates
What are possible irritants
sodium hypochlorite
EDTA
chlorhexidine digluconate (0.2 or 2%)
sterile saline
When do we use chlorhexidine digluconate
used if sodium hypochlorite contraindicated such as a perforation site
If chlorhexidine and NaOCl are mixed what forms
chloroaniline
cytotoxic and carinogenic
uncertain bioavailability
What are properties of an ideal obturation material
easily manipulated with ample working time dimensionally stable by tissue fluids seals the canal laterally and apically non irritant impervious to moisture unaffected by tissue fluids inhibits bacterial growth radiopaque does not discolor tooth sterile easily removed if necessary
What is the most common core material
GP
What is Gp
natural rubber and gutta percha are polymers of isoprene
How does Gp exist
as 2 phases - alpha and beta
What is the alpha GP phase
naturally occurring form
when heated above 65 degrees it melts into amorphous phase
cooled slowly returns to alpha phase
cooled rapidly recrystalises as beta phase
What is the beta phase used in
commercially prepared dental GP
What is the composition of Gp cones
20% gp
65% zinc oxide
10% radiopacifiers
5% plasticizer
Wha are the different types of GP cones
standardised
non standardised
size matched
What is the function of a sealer
seals space between dentinal wall and core
fills void and irregularities in canal, lateral canals and between GP points used in lateral condensation
lubricates during obturation
What are the properties of an ideal sealer
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 pretreatment
What is zinc oxide and eugenol made of
the mixing vehicle is mostly eugene
finely sifted zinc oxide is used to enhance flow
radiopacity is less than GP
can be modified with germixides
has Rosin or canada balsam to increase dentine adhesion
has corticosteroids
What is zinc oxide and eugenol effect as
an antimicrobial and may afford cytoprotection
What does zinc oxide and eugenol contain that allows for its antimicrobial character
resin acids in the Rosin affect lipids in the cell membrane
although toxic, amy overall be beneficial with antimicrobial effect combined with cytoprotecitve effects
What is the setting of zinc oxide and eugenol
chemical process combined w physical embedding of zinc oxide in a matrix of zinc eugenolate
eugenolate formation constitutes hardening - CaOH acerbates this process so must be removed from canals
free eugonel which remains can act as an irritant
lose volume this time due to dissolution - resins can modify this
Describe benefits and disadvantages of GI sealers
advocated due to dentine bonding properties
removal upon pretreatment is difficut
minimal antimicrobial activity
little clinical data to support use
Describe goods and bads of epoxy resin sealers
slow setting - 8 hours
good sealing ability
good flow
initial toxicity declining after 24h
Describe the goods and bads of calcium silicate sealers
high pH during the initial 24h of setting
hydrophilic
enhanced biocompatibiltiy
does not shrink on setting
non resorbable
excellent sealing ability
quick set - 3 to four hours -requires moisture
easy to use
What is grey MTA made of
tricalcium silicate dicalcium silicate tricalcium aluminate tetracalcium aluminoferrite bismuth oxide
What are characteristics of grey MTA
earliest formulations
less toxic than portland cement
better setting characteristics
tooth discoloration
What are characteristic of white mTA
smaller particle size
reduced discoloration
What is white mTA made of
tricalcium silicate dicalcium silicate calcium aluminate bismuth oxide calcium sulphate dehydrated
What is the setting reaction of MTA like
they are hydraulic cements (require water for setting)
they’re composed of several phases
when mixed with water there is a chemical reaction that occurs between these phases and water
Why is the fact that zinc oxide loses volume with time due to dissolution a negative thing
we want stability and the problem is they dissolve with team so the apical seal can be diminished can can result in problems
What is the negative to epiphany resin sealers resin sealers
they require a self etch primer and its hard to do this effectively in the RC space
What are the components of dual cure resin composite sealers (epiphany)
used with resilon bisGMA UDMA hydrophilic difunctional methacrylates fillers of CAOH, barium sulphate, barium glass and silica
What is the advantage of UDMA resin based sealers
they are hydrophilic so can get good penetration into tubules
biocompatible
good radiopacity
What is the main bio ceramic cement
MTA
biodentine
What is so good about bioceramics
they induce osteogenesis and encourage bone formation
this is related to the change of pH
hydroxyapatite layer forms on the surface
cementum forms directly on top of MTA
What are the 3 stages of MTA setting
mixing
dormancy
hardening
What are issues with MTA
extended setting time (modifications made)
handling difficult
works best in areas where its hard to control moisture e.g large open apex
do not work in oral cavity as takes so long to set it will be washed away by saliva
discoloration
What makes biodentine good
quicker setting
direct pulp capping
reduced staining
