endo Flashcards
what are the design objectives of root canal treatment
create a continuously tapering funnel shape
maintain the apical foramen in the original position
keep the apical opening as small as possible
what medical, clinical and radiographic considerations should you take into account when performing case selection for endodontics
medical - pregnancy (endo should only be done as an emergency in first trimester); endo contraindicated in patient’s who have had MI in the past 6 months
clinical - amount of remaining tooth structure; pus/abscess; periodontal disease (mobility or furcation involvement)
radiograph - anatomy of the roots, previous root treatment (length, voids, number of canals, apical and coronal seal); peri apical radiolucency; bone levels
what are the design principles for the access cavity
allow removal of the entire contents of the pulp chamber
allow visualisation of the pulp floor and canal orifices
allow direct access to the apical 1/3 of the canal for instrumentation
allow retention and support of a temporary filling
provide a reserved for canal irrigant
be as conservative as possible
provide smooth walled preparation with no overhangs and unimpeded straight line access of instruments
what instruments should you use when removing the roof of the pulp chamber and locating canal orifices
safe ended access bur; DG16 endo probe
how do you ensure safe us of sodium hypochlorite
27 gauge side vented needle securely attached to a 3ml string that is never >3/4 full
depress string with finger not thumb
never lock the needle in the canal
have a rubber stop 2mm short of working length
careful pre op radiograph
patient provided with bib and eye protection
isolate the tooth with dental dam and check the seal with chlorhexidine before using NaOCl
clearly label all syringes
always pass the syringe behind the patient’s head
what are the signs of sodium hypochlorite extrusion
pain
swelling
bruising
haemorrhage
numbness/ tingling
airway obstruction
what are the risk factors that could lead to sodium hypochlorite extrusion
excessive pressure when irrigating - flow rate should be 1ml per 15s
needle locked within canal
loss of control of working length
large apical diameter (root resorption or immature roots)
anatomical factors (proximity to sinus)
higher NaOCl concentration
how would you manage a sodium hypochlorite extrusion
stop treatment
remain calm
explain to patient what has happened
allow bleeding to continue into the canal until haemostasis observed
provide LA block in the aerate help with pain
do not obturate this visit - a steroid containing intra canal medicament should be placed with minimal pressure
seal the coronal access cavity
POI = cold compresses during the first few days, warm compresses reduce soft tissue swelling, advise analgesia
review within 24h
refer to A&E if severe or patient worsening
what are the dimensions of ISO stainless steel hand files
2% taper along its length
21, 25 or 31mm long; all with 16mm cutting flutes
10k file = 0.1mm tip (divide size by 100 to get the diameter of the tip in mm)
diameter at handle end = apical size + 0.32mm
how is watch winding technique used
back and forward oscillation of 30-60 degrees
used for passing small files through canals
how is balanced force technique used
1/4 turn clockwise to engage dentine then 1/2 turn anti clockwise with apical pressure to strip dentine away
used for larger K files
what are the functions of root canal irrigants
remove the smear layer
provide lubrication
flush out debris
dissolve organic tissue
disinfect the root canal
why is coronal flaring important
avoids hydrostatic pressure building up int he canal
early removal of heavily contaminated contents
improved straight line access to apical 1/3
how do you determine corrected working length
subtract 0.5-1mm from the electronic apex locator 0 reading
subtract 1mm from the radiographic apex in the working length radiograph (paralleling technique with a 15k file in the canal to estimated working length)
why is recapitulation important
10k fil mis taken to WL to ensure debris is not packing apically
how is step back performed
take a wider file 0.5-1mm shorter than the file before it until the apical prep reaches the coronal preparation
what is estimated working length
based on the pre op radiograph (distance between coronal reference point and the radiographic apex minus 1mm)
length at which instrumentation should be limited
what is corrected working length
the length at which instrumentation and obturation should be limited
determined using the electronic apex locator or working length radiograph
what sealers can be used for cold lateral obturation
resin based
GIC
zinc oxide eugenol
calcium hydroxide
briefly describe cold lateral compaction
master GP cone is dipped in sealer then fitted to CWL (ensure tug back is exhibited)
size matched finger spreader is placed next to the master GP cone 1-2mm short of the CWL, pushing the master cone against the canal wall
accessory point is dipped in sealer and inserted into the canal as the finger spreader is removed
this is repeated until the canal is filled
use a heated excavator or cutter to remove GP at the level of the canal orifice
what are the laws of symmetry
(all except maxillary molars)
1 - the orifices of the canals are equidistant form a line drawn in a mesial distal direction through the pulp chamber floor
2 - the orifices of the canals lie perpendicular to the line drawn in a mesial distal direction in the centre of the pulp chamber floor
what is the law of colour change
the floor of the pulp chamber is darker than the walls
what are the laws of orifice location
1 - the orifices are always located at the junction of the walls and the floor
2 - the orifices of the canals are always located at the angles of the floor-wall junction
3 - the orifices of the root canals are located at the terminus of the root developmental fusion lines
what is straight line access
straight access to the first point of curvature or the apex, whichever comes first
this is needed to reduce stress on instruments and reduces the chances of separation/ ledges/ perforations
gates glidden burs can be used to remove lips of dentine
what is the benefit of using NiTi ProTaper files
super-elasticity so flexible in curved canals
- it can be strained more than other alloys before permanent deformation
- less chance of transportation, zipping, ledging
- they have a variable taper, differing from stainless steel’s continuous 2% taper
- increased cutting efficacy
- less instruments; simple sequence
how do you create a glide path
confirm straight line access and explore anatomy with a 10k then 15k file to apex after coronal flaring with S1 to 2/3 working length
use watch winding to reach apex and expand apical portion to ensure when S1 and S2 taken to WL the delicate tip isn’t overloaded so limits risk of root fracture
why is it important to prepare the apex to 3 sizes larger than the first file that binds
removes dead pulp tissue
more space for irrigant
allows adequate obturation
the dentine should be bright white (= healthy)
how do you perform apical gauging
equivalent k file to final apical ProTaper file should be used to CWL and will not advance even with light apical pressure
if k file goes beyond working length then expand prep until control determined, then obturate and check tug back with master apical GP cone
use k file as taper of F2 means that it might bind coronally before apically
why is instrumentation of the canal important
remove infected soft and hard tissue from inside the root canal
give disinfecting irritants access to apical canal space
create space for delivery of medicaments and subsequent obturation
retain the integrity of radicular structures
what is the irrigation protocol after shaping is complete
17% EDTA for 1 minute
3% NaOCl 30ml for 10 minutes
what is a barbed broach used for
extirpating the pulp, not enlarging
must not engage canal walls
extremely fragile instrument will break if misused - select the largest size that fits freely in the canals
what are the disadvantages of NiTi instruments
expensive
access can be difficult in posterior teeth
unsuitable for complex canal anatomy
what are the properties of using a true reciprocation technique
mimics manual movement
reduces risks associated with continuously rotating a file through canal curvatures
decreased cutting efficacy
requires inward pressure
limited capacity to auger debris out of a canal
moves 150 degrees counter clockwise; 30 degrees clockwise
moved in and out 3 times in a slow pecking motion; <3mm into the canal with very light pressure; instrument removed from canal, debris cleaned from the flutes, canal irrigated, repeat advancing 1mm per cycle
why do instruments separate
torsional stress - extensive instrument surface encounters excessive friction on canal walls; instrument tip is larger than the canal section to be shaped so the tip locks and torque exceeds critical level
flexural stress - repeated cyclic metal fatigue from generation of tension/compression cycles; cannot be influenced by clinician
