endodontics Flashcards
problems that can arise with post crowns - 4
perforation
core fracture
root fracture or crack
post fracture
clinical assessment of a RCT treated tooth involves assessing…
coronal seal - leakage, caries?
amount of remaining tooth - ferrule
if tooth is restorable
sinus, swelling, TTP, mobility, pocketing
when radiographically assessing a RCT what do you look for
Root filling - length, voids?
unfilled or missed canals
shape of canals
bone support
pathology - radiolucency or resorption or perforations
endo complications
fractured instrument
perforation
lack or no ferrule after RCT
give a cause of RCT failure
coronal micro leakage - ingress of micro-organisms into RC system
restoration option for an anterior tooth with intact marginal ridges
veneer or composite restoration
restoration options for an anterior tooth with intact marginal ridges and discoloured crown
bleaching
veneer
crown
restoration options for an anterior tooth with intact marginal ridges and discoloured crown
bleaching
veneer
restoration options for anterior teeth with marginal ridges destroyed
core build up with crown
post crown.
what is the function of a post and a core
gains intra-radicular support for a definitive restoration
core provides retention for crown
post provides retention for core
true or false, tooth is weakened when prepared for a post
true
what length of GP is required to be left apically for post placement
3-5mm
how wide should a post be
no more than 1/3 of the width of the narrowest point of root
at least 1mm of circumferential coronal dentine present
minimum post length to crown ratio
1:1
what would be sufficient alveolar support for a post and core
the alveolar bone is half the length of post at least
what is a ferrule
dentine collar - encirclement of 1-2mm of vertical axial tooth structure within walls of crown
what is the purpose of ferrule
prevents tooth fracture
for post placement what height and width of ferrule is required
at lest 1.5mm height and width
post materials - 3
metal - cast metal, stainless steel
ceramic - zirconia
fibre - glass, carbon
what are the two shapes of post
tapered
parallel (more retentive)
what is a Nayyar core
RCT removed and amalgam packed into the canals, tooth is built up
AVOID
core materials - 2
composite - good aesthetics, bonds to tooth
amalgam - retention required and can’t prep straight away, needs to set for 24hrs
what is a core build up
internal part of tooth is built up with a restorative material to provide retention and resistance for permanent restoration
advantages of prefabricated posts - 3
no impressions or lab visit
immediate prep of core chair side
large selection of design and material
advantage and disadvantage of custom post
unified post and core
2 visits required - impression and fit, risk of contamination
advantage of parallel sided post
avoids wedging
how to prevent rotation of post in absence of coronal dentine
anti rotation notch - small vertical groove in canal
taper of a core
6 degrees
why are posts not routinely used in molars
disadvantages outweigh advantages
narrow roots - post prep may perforate
core retention can be optioned from undercuts and bonding agents
if there is not coronal tissue on a molar, what canal would you insert a short post into
largest and straightest RC
distal mandibular
palatal maxillary
why is cuspal protection important - 3
prevents catastrophic fracture
maintains coronal seal
prevents microbial ingress
why is cuspal protection important - 3
prevents catastrophic fracture
maintains coronal seal
prevents microbial ingress
design objectives of root canal
continuously tapering funnel shape
apical foramen in original position
apical foramen as small as possible
instrument to detect canal orifice
DG16 endodontic explorer
where should GP be cut
orifice or just below orifice level
what material are k files made of
stainless steel
flexible k files nickel titanium
motions you can use an endo file
filing
reaming
watch winding
balanced force
envelope of motion
which endo file technique can be described as back and forward oscillation of 30 and 60 degrees with light apical pressure
watch winding
which endo file technique can be described as 90 degree turn clockwise with apical pressure then 180 degree counter clockwise turn with continued pressure
balanced force technique
what is cyclic fatigue
when rotating file in a curvature there is a generation of compression and tension cycles on each side of the file - leads to failure
cross section of reciprocal file
s shape
what angles of rotation does reciprocal use
150 CC
then
30 CW
signs of RCT failure
clinical signs and symptoms
enlargement of existing periradicular lesion
development of new periradicular lesion
persistence of periradicular lesion associated with tooth that had RCT at least 4 years ago
indications for non surgical RC re treatment
intra radicular infection
new complex restoration with a technically poor RCT
loss of coronal seal
solvent that can be used to soften and help remove GP for re treatment
eucalyptus oil - more GP and sealer left behind if use solvent though
what would you write on a lab prescription for a post and core
please contract an post and core
para post - colour
core 6 degree taper and 2mm space in occlusion for crown
What factors would you consider when deciding on post options?
root canal anatomy - narrow and curved will need a custom post, prefabricated can be used in straight and wider
remaining tooth structure - requires minimum ferrule of 1.5mm
aesthetics - tooth coloured post in aesthetic areas
What factors do you consider important when deciding if a tooth is restorable?
remaining tooth structure - ferrule
RCT status
fractures
bone levels
what is stress in DMS
deforming force measures across given area
=F/A
what is strain
response of a material to stress
what is the elastic limit
a set valid representing the maximum strain that when applied to a file allows the file to return to original dimensions
what is elastic deformation
reversible deformation that does not exceed elastic limit
what is plastic deformation
permanent deformation occurring when elastic limit exceeded - the point that a plastic instrument will fracture
two ways Endodontics instrument can fail
cyclic fatigue
torsional fatigue
what is torsional fatigue
instrument in canal binds to dentine and rotated
bound portion does not rotate and the other portion does leading to torsion and elastic limit is exceeded
leads to failure
how do you prevent endo instrument fracture
create a manual guide path - creates space for tip
straight line access
gentle pressure and constantly moving
what component of stainless steel prevents rusting
chromium - forms passivation layer of chromium oxide
what step in manufacture of endo files does work hardening occur
the twisting of the files
what is work hardening
strengthening of a material by plastic deformation
dislocates crystalline lattice
dislocations create resistance to further dislocations
how does NI-Ti not conform to typical properties of metals
displays super elasticity - application of stress does not result in usual proportional strain
what is the effect of temperature on NiTi crystal structure
martensite and austenite are temperature dependent
crystal attic structure is altered by temperature
martensite form is soft, ductile - room temp and below
austenitic form is strong and hard - warmer temperatures
what is the taper of an instrument
diameter change along working surface
taper of a K file
2%
function of flute on instruments
grooves to collect dentine and soft tissues
what is the helix angle
angle cutting axis forms with long axis of file
role of an irritant in Endodontics
removal of debris
lubrication
antimicrobial - kill bacteria and viruses
primary irritant for endo
NaOCL
sodium hypochlorite 3%
what is responsible for antibacterial activity in sodium hypochlorite
HOCl
hypochlorus acid
factors important for hypochlorite function
concentration
volume
contact
mechanical agitation
exchange
why is it important to remove the smear layer before obturation
prevents sealer penetration
interferes with disinfection
what is the smear layer
organic pulp and inorganic dentine debris
what do we use to remove smear layer
17% EDTA
irritants can interact - give an example of a consequence of irritant interaction
interaction with NAOCl forms para chloroaniline
cytotoxic and carcinogenic
ideal properties of an obturation material
easily manipulated
non irritant
radiopaque
seals canal laterally and apically
impermeable to moisture
GP is a trans isomer of what polymer
polyisoprene
what are the two forms of GP and how are they formed
Alpha - naturally occurrent
beta - formed when alpha phase heated above 65 and cooled RAPIDLY - recrystallises as beta
what phase of GP is used in dental GP
beta
components of GP cones
20% GP
65% zinc oxide
radio pacifiers and plasticisers
what is the function of a sealer - 3
lubricate during obturation
seal birds and irregularities in canal - lateral canals
seal space between dentinal wall and core
ldeal properties of a sealer
easily mixed
no shrinkage on set
insoluble
radiopaque
example of sealer used in endo
zinc oxide and eugenol
disadvantage of ZOE sealers
unstable - lose volume with time - can impact apical seal
what is MTA used for - mineral trioxide aggregate
pulp capping and root end filling
disadvantage of MTA
tooth discolouration
long set time
