endo

Question 1

what are the design objectives of root canal treatment

Answer 1

create a continuously tapering funnel shape
maintain the apical foramen in the original position
keep the apical opening as small as possible

Question 2

what medical, clinical and radiographic considerations should you take into account when performing case selection for endodontics

Answer 2

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

Question 3

what are the design principles for the access cavity

Answer 3

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

Question 4

what instruments should you use when removing the roof of the pulp chamber and locating canal orifices

Answer 4

safe ended access bur; DG16 endo probe

Question 5

how do you ensure safe us of sodium hypochlorite

Answer 5

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

Question 6

what are the signs of sodium hypochlorite extrusion

Answer 6

pain
swelling
bruising
haemorrhage
numbness/ tingling
airway obstruction

Question 7

what are the risk factors that could lead to sodium hypochlorite extrusion

Answer 7

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

Question 8

how would you manage a sodium hypochlorite extrusion

Answer 8

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

Question 9

what are the dimensions of ISO stainless steel hand files

Answer 9

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

Question 10

how is watch winding technique used

Answer 10

back and forward oscillation of 30-60 degrees
used for passing small files through canals

Question 11

how is balanced force technique used

Answer 11

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

Question 12

what are the functions of root canal irrigants

Answer 12

remove the smear layer
provide lubrication
flush out debris
dissolve organic tissue
disinfect the root canal

Question 13

why is coronal flaring important

Answer 13

avoids hydrostatic pressure building up int he canal
early removal of heavily contaminated contents
improved straight line access to apical 1/3

Question 14

how do you determine corrected working length

Answer 14

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)

Question 15

why is recapitulation important

Answer 15

10k fil mis taken to WL to ensure debris is not packing apically

Question 16

how is step back performed

Answer 16

take a wider file 0.5-1mm shorter than the file before it until the apical prep reaches the coronal preparation

Question 17

what is estimated working length

Answer 17

based on the pre op radiograph (distance between coronal reference point and the radiographic apex minus 1mm)

length at which instrumentation should be limited

Question 18

what is corrected working length

Answer 18

the length at which instrumentation and obturation should be limited

determined using the electronic apex locator or working length radiograph

Question 19

what sealers can be used for cold lateral obturation

Answer 19

resin based
GIC
zinc oxide eugenol
calcium hydroxide

Question 20

briefly describe cold lateral compaction

Answer 20

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

Question 21

what are the laws of symmetry

Answer 21

(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

Question 22

what is the law of colour change

Answer 22

the floor of the pulp chamber is darker than the walls

Question 23

what are the laws of orifice location

Answer 23

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

Question 24

what is straight line access

Answer 24

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

Question 25

what is the benefit of using NiTi ProTaper files

Answer 25

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

Question 26

how do you create a glide path

Answer 26

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

Question 27

why is it important to prepare the apex to 3 sizes larger than the first file that binds

Answer 27

removes dead pulp tissue
more space for irrigant
allows adequate obturation

the dentine should be bright white (= healthy)

Question 28

how do you perform apical gauging

Answer 28

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

Question 29

why is instrumentation of the canal important

Answer 29

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

Question 30

what is the irrigation protocol after shaping is complete

Answer 30

17% EDTA for 1 minute
3% NaOCl 30ml for 10 minutes

Question 31

what is a barbed broach used for

Answer 31

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

Question 32

what are the disadvantages of NiTi instruments

Answer 32

expensive
access can be difficult in posterior teeth
unsuitable for complex canal anatomy

Question 33

what are the properties of using a true reciprocation technique

Answer 33

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

Question 34

why do instruments separate

Answer 34

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