endo materials Flashcards
endo materials
instruments irrigants intra-canal medicaments obturation materials sealers pulp capping materials root end filling materials
functions of instruments
remove hard and soft tissues
removes MOs
creates space for disinfectants/medicaments
creates appropriate shape for disinfection
stress
deforming force measured across a given area
tensile/compressive/shear/torsional
stress = F/A
stress concentration point
abrupt changes in the geometric shape of a file that leads to a higher stress at that point
strain
response of a material to stress
amount of deformation a file undergoes
change in length/length
elastic deformation
reversible deformation that does not exceed elastic limit
elastic limit
a set value representing the maximal strain that when applied to a file allows the file to return to original dimensions
shape memory
alloys - can be deformed at one temp but when heated/cooled return to their original shape
= behave differently in the canal as they do outside
plastic deformation
permanent bond displacement occurring when plastic limit exceeded
plastic limit
the point at which a plastic deformed file breaks
- instrument separation - can affect outcome but not always
cyclic fatigue
freely rotating - not bound in curved canals generation of tension/compression cycles - compression on one side tension on the other failure e.g. MB canal of molar
why might an instrument that breaks due to cyclic fatigue be easier to remove?
freely moving
torsional bound so may be more difficult
torsional fatigue
when bound in canal
instrument binds in RC, is further rotated - stress in torsion, torque
structure of metal will undergo changes - reversible or irreversible - depends on amount of rotation when instrument binding
elastic phase - elastic limit - plastic phase - fracture
elastic phase
no irreversible changes
plastic phase
irreversible changes in structure of metal
in reciprocation how should the clockwise and anticlockwise angles of rotation be set?
lower than the elastic limit
safer procedure the lower the angles of rotation
as long as can still cut dentine, advance apically in the canal and remove the cutting debris in a coronal direction
preventing instrument fracture
training
create a manual glide path
crown-down instrumentation technique to ensure straight line access
electric speed and torque controlled motor
NiTi files - constant motion using gentle pressure
avoid triggering or disable the autoreverse mode
avoid rotary files in abruptly curved or dilacerated canals
classification of instruments
manually operated low-speed instruments e.g. GG engine-driven NiTi rotary instruments engine-driven instruments that adapt to canal shape engine-driven reciprocating instruments US instruments
SS components
alloy - Fe, C, Cr
Ni maybe
improved carbon steel
rusting = all single use now
Cr in SS
13-26%
prevents rusting
passivation layer or chromium oxide
SS instrument manufacture
cut then twist - machined SS wire - square/triangular - twisted - work-hardening cut - machine SS wire into desired shape - work-hardening
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
observed work hardening
what can work hardening lead to?
cyclic fatigue
Nitinol
equiatomic alloy of Ni and Ti
exotic metal - does not conform to typical rules of metttalurgy
superelasticity - application of stress does not result in usual proportional strain
NiTi crystal lattice structures
temp dependent structures martensite and austenite
crystal lattice structure altered by temp or stress
character and proportions determine mechanical properties of metal
martensite form - soft, ductile and easily deformed
austenitic form - quite strong and hard
taper
diameter change along working surface
flute
groove to collect dentine and ST
leading/cutting edge
forms and deflects dentine chips
land
surface extending between flutes = can be flat, grooved or concave
affects how it behaves in canal
relief
reduction in surface of land
helix angle
angle cutting axis forms with long axis of file
constant helix angle
can behave like a screw (bad)
modify helix angle
can’t behave like a screw
positive rake angle
provides the active cutting action of the K3
wide radial land
provides blade support while adding peripheral strength to resist torsional and rotary stresses
radial land relief§
reduces friction on the canal wall
third radial land
stabilises and keeps the instrument centred in the canal and minimised ‘over engagement’
irrigant ideal properties
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
NaOCl conc
3%
NaOCl chemistry
ionises in water into Na+ and OCl-
establishes equilibrium with hypochlorous ion HOCl
acid/neutral HOCl predominates
pH 9 and above OCl- predominates
HOCl is responsible for antibacterial activity
NaOCl properties
effect on organic material
inability to remove smear layer by itself
possible effect on dentine properties
factors important for NaOCl function
concentration volume contact mechanical agitation - MDI exchange
smear layer
formed during prep
organic pulpal material and inorganic dentinal debris
superficial 1-5um with packing into tubules
bacteria contamination, substrate and interferes with disinfection
prevents sealer penetration
removal of smear layer options
17% EDTA
10% citric acid
MTAD (mixture of a tetracycline isomer, an acid and a detergent)
sonic and US irrigation
NaOCl and CHX interaction
forms parachloroaniline
cytotoxic and carcinogenic
uncertain bioavailability
irrigant selection
NaOCl and EDTA shouldn’t be present in root canal at same time
order they should be used debate
sodium hypochlorite (parcan)
3%
dissolves organic material, bacteriocidal
disinfection
30ml per canal, continual irrigation time for at least 10mins following completion of prep and prior to obturation
EDTA usage
17%
smear layer removal
penultimate rinse for 1min
3ml per canal
Chlorhexidine digluconate (Corsodyl)
0.2%
check dam integrity/disinfect tooth surface
Chlorhexidine digluconate (GlucoChex)
2%
antimicrobial
suspect iatrogenic damage
only use if NaOCl contraindicated
sterile saline (Baxter)
wash out canal is NaOCl accident suspected
properties of an ideal obturation material
easily manipulated with ample working time dimensionally by tissue fluids stable seals the canal apically and laterally non-irritant impervious to moisture unaffected by tissue fluids inhibits bacterial growth radiopaque does not discolour tooth sterile easily removed if necessary
GP production
produced from juice of trees of the sapodilla family
trans isomer of polyisoprene
GP a and B forms
exists in 2 crystalline forms a and B
a phase is the naturally occurring form
a phase heated above 65 degrees melts into amorphous phase
cooled slowly returns to a phase
cooled rapidly recrystallises as B phase
B phase used in commercially prepared dental GP
GP constituents
GP 20%
zinc oxide 65%
radio pacifiers 10%
plasticisers 5%
types of GP cones
standardised
non-standardised
size matches
what should be done to GP cones before obturation?
put in NaOCl as not sterile when packaged
modified GP
can impregnate with bio ceramics and antimicrobials
- enhance bonding between GP and sealer
sealer functions
seals space between dentinal wall and core
fills voids and irregularities in canal, lateral canals and in between GP points used in lateral condensation
lubricates during obturation
properties if an ideal sealer
exhibits tackiness to provide good adhesion exhibits a hermetic seal (air tight) 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 re-tx
zinc oxide and eugenol chemistry
mixing vehicle mostly Eugenol
finely sifted ZnO to enhance flow
can be modified with germicides
rosin or canada balsam to increase dentine adhesion
corticosteroids
setting - chemical and physical embedding of ZnO in matrix of Zn eugenolate
eugenolate formation - hardening
- CaOH accelerates so must be removed from canals
free eugenol which remains can act as an irritant
zinc oxide and eugenol properties
less radiopaque than GP
ZnO antimicrobial - may be cytoprotective
resin acids 90% of rosins affect lipids in cell membrane therefore strongly antimicrobial/cytotoxic
although toxic may overall be beneficial with long lasting antimicrobial and cytoprotective effects
lose vol with time due to dissolution - resins can modify this
- problem - lose vol - eventually washed away
GI sealers
advocated due to dentine bonding properties
removal upon re-tx is difficult
minimal antimicrobial activity
little clinical data to support use
resin sealers e.g. AHPlus, AH26
epoxy resin paste-paste mixing slow setting 8hrs good sealing ability good flow not really bioactive initial toxicity declining after 24hrs radiopaque biocompatible dimensionally stable
epiphany
dual cure dental resin composite sealer - used with Resilon
requires self-etch primer
EndoRez
UDMA resin-based sealer hydrophillic good penetration into tubules biocompatible good radiopacity
calcium silicate sealers
high pH12.8 during initial 24hrs of setting hydrophillic enhanced biocompatibility dimensionally stable non-resorbable excellent sealing ability quick set 3-4hrs - requires moisture easy to use osteo and bioinductive - stimulates a response in the body
medicated sealers
sealers containing paraformaldehyde not acceptable
lead and mercury components removed
cytotoxic and carcinogenic
severe and permanent effects (toxic) on PR tissues
pulp capping/root end filling material uses
pulp cap pulpotomy and pulp regeneration lateral perforation repair apicoectomy apexification root resorption repair furcation perforation repair
grey MTA
earliest formulations
less toxic than Portland cement
better setting characteristics
tooth discolouration
tricalcium silicate, dicalcium silicate, tricalcium aluminate, tetracalcium aluminoferrite, bismuth oxide
white MTA
smaller particle size
reduced discolouration
one that is typically used now
tricalcium silicate, dicalcium silicate, calcium aluminate, bismuth oxide, calcium sulphate dehydrated
what is MTA based on?
cement
MTA setting reaction
hydraulic cements composed of several phases
hydration - mixed with H2O - chemical reaction
white and grey diff setting reactions
mixing, dormancy, hardening
modifications to change characteristics
extended setting times
bio ceramic cements
shorter setting times
tissue response
- no areas of fibrosis/chronic inflammation
- just see induction of cementogenesis etc
the ideal root filling?
generally a core material and sealer
always sealer used to create a fluid-tight seal
now shift to a sealer-based obturation
single point obturation with excess of sealer - still need a GP cone to get apical control
CaOH properties
bacteriocidal and bacteriostatic properties
high pH
adheres directly to dentine
thin so won’t reduce strength of restorative material
won’t dissolve in biological liquids
CaOH high pH
stimulates fibroblasts for reparative dentine formation - stimulates decalcification of demineralised dentine by stimulating pulpal cells
neutralises low pH from acidic restorative materials
