instrumentation of the root canal system

Question 1

chemo(bio) mechanical preparation

Answer 1

Chemo =
Irrigate to kill micro
Organisms
Remove smear layer

Mechanical =
Prepare shape
Flush out

Question 2

chemomechanical aim

Answer 2

Shape the canal
Allows delivery of sodium hypochlorite to working length
Creates shape to obturate

Question 3

challenges of RCT prep

Answer 3

root canal system is very complex

number, length, curvature and diameter of canals can vary considerably

vertucci classification

teeth are weird

Question 4

design objective

Answer 4

creating a continuous tapering funnel shape
maintain apical foramen
keep apical opening as small as possible

Question 5

estimated working length

Answer 5

Estimated length at which instrumentation should be limited.

Obtained by measuring pre-operative radiograph to determine distance between coronal reference point and radiographic apex then subtracting 1mm.

Question 6

corrected working length

Answer 6

Length at which instrumentation and subsequent obturation should be limited

Obtained by the use of an electronic apex locator and/or working length radiograph.

Question 7

master apical file

Answer 7

The largest diameter file taken to working length and therefore represents the FINAL prepared size of the apical portion of the canal at the working length

Question 8

types of rct motion

Answer 8

Filing
Reaming ( warning)
Watch-winding
Balanced Forced Motion
Envelope of Motion

Question 9

watch winding

Answer 9

back and forward of 30-60 degrees
light apical pressure
effective with k files
useful for passing small files

Question 10

balanced force

Answer 10

remember envelope of motion

reported that the resistance of the dentin, as it circumferentially contacted the flutes of a file in a curved root canal, would be sufficient to override and mask any tendency of the file to straighten during rotational instrumentation.

1 = Insert file and engage the file in the canal wall with a quarter-clockwise rotation turn,
2= Maintain pressure and turn the file in a three-quarters counter-clockwise direction to cut the dentine of the canal wall
3= Turn the file clockwise without pressure
4= Remove the file from the canal.

repeat 3 times and irrigate

Question 11

initiate irrigation protocol

Answer 11

EDTA 17% for 1 minute

Sodium hypochlorite 3%, 30 ml for 10 minutes.

Slow injection, Don’t use thumb!!!!!!!

Revise restorative synopsis and chemo mechanical disinfection section.

Question 11

barbed broach

Answer 11

Used for EXTIRPATING, NOT enlarging

Formed from a tapered round shaft by lifting up portions of metal of the shaft almost at a right angle to the shaft

Must not engage the canal walls

Extremely fragile instrument, and will break easily if misused.

Elevated barbs engage the pulp tissue and remove it from the canal
The largest size broach which will fit freely in the canal is selected

Question 12

iso colour code

Answer 12

white = 15 45
yellow = 20 50
red = 25 50
blue = 30 60
green = 35 70
black = 40 80

Question 13

stainless steel instruments

Answer 13

ISO-sized instruments
All have 16mm cutting flutes

Each file is named according to its diameter at the first rake angle – D1
Taper is 0.32 over the 16mm, or 0.02 per millimetre
Diameter at D2 = apical size + 0.32mm

Question 14

hedström Files

Answer 14

steel blank

used in a filing motion, cuts on withdrawal
good cutting efficiency but can cause iatrogenic damage
no longer used for canal preparation
useful for removing gutta-percha or fractured instruments in cases of retreatment

Question 15

reamer

Answer 15

triangular shaft
cuts edges parallel to long axis

rotated 1/4 to 1/2 turn clockwise to cut as advanced to length

must be in contact with the walls of the canal to be effective, otherwise breaks

Question 16

k-files

Answer 16

square tapered shaft

cutting edges are perpendicular to the long axis of the instrument

can be used in a filing motion - advanced to the full working length rotated 1/4 to 1/2 turn clockwise, and withdrawn while apply lateral pressure.

do not use larger instrument too quickly

Question 17

nickel-titanium

Answer 17

developed in 1960s for space program
Nitinol - Nickel Titanium Naval Ordnance Lab

shape memory effect after heat treatment
SUPERELASTICITY

Question 18

components of an endodontic rotary instrument

Answer 18

Taper – diameter change along working surface

Flute – groove to collect dentine and soft tissue

Leading/Cutting edge – forms and deflects dentine chips

Land – surface extending between flutes

Relief – reduction in surface of land

Helix angle – angle cutting axis forms with long axis of file

Question 19

superelasticity

Answer 19

Can be strained more than other alloys before permanent deformation

Allows NiTi files to be placed in curved canals with less lateral forces exerted

Less transportation, zipping and ledging

More centrally placed preparation in harmony with the original canal shape

Question 20

advantages of NiTi versus SS

Answer 20

increased FLEXIBIULITY in larger sizes and tapers
increased cutting EFFICIENCY
if used appropriately good SAFETY in use
can be more user friendly with less instruments and simple sequences

Question 21

disadvantages

Answer 21

instrument fracture
expense
access can be difficult in posterior teeth
unsuitable for complex canal anatomy

Question 22

pro taper hand use

Answer 22

S1 -> S2 -> Sx

or F - finishing files = good for large files

Question 23

rotary instrumentation

Answer 23

guidelines:

straight line access
cross-sectional diameter
root canal system anatomy
speed and sequencing
lubrication and a “light touch”

Question 24

creating a glide path

Answer 24

confirm straight-line access
explore anatomy
always introduce files 10-25 to resistance only (coronal only)
coronal flare
size 10 with watch winding establish apex
irrigate and repeat using sizes 15 (WW) and 20 (BF)

Question 25

when using rotary

Answer 25

remember to clean the debris
irritate
make sure canal is free to 1m beyond the prepared canal section

Question 26

files are one use only because

Answer 26

of prion decontamination

Question 27

instrument separation

Answer 27

Torsional stress
Extensive instrument surface encounters excessive friction on canal walls
Instrument tip is larger than canal section to be shaped
Tip may lock, torque exceeds critical level

Flexural stress
Repeated cyclic metal fatigue
Cannot be influenced by clinician

Question 28

cyclic fatigue

Answer 28

free rotation in a curvature
generation of tension/compression cycles
cyclic fatigue
failure

Question 29

torsional fatigue

Answer 29

If an instrument binds in the root canal and is further rotated, it will be subjected to stress in torsion, torque. The structure of the metal will undergo changes. These changes can be reversible or irreversible depending on the amount of the rotation when the instrument is binding. In this example, any rotation between 0 and 400 degrees will not cause irreversible changes to the structure of the metal. Any rotation beyond 400 degrees when the instrument is binding will cause irreversible changes in the structure of the metal.

In the end, the instrument in this example fractures at approximately 1100 degrees of rotation. This zone between 0 and 400 degrees where the changes are reversible is called the elastic phase. The zone from 400 degrees to the point of fracture at around 1100 degrees is to the plastic phase. The point of transition between the elastic phase and the plastic phase is called the elastic limit. In this example the elastic limit is at approximately 400 degrees. If a rotary instrument engages dentine and the motor keeps rotating it, the metal of the instrument will undergo irreversible changes. This happens a first time, a second time and a third time and so on… every time the metal will undergo irreversible changes which will cause torsional fatigue and eventually lead to fracture. In reciprocation, the clockwise and counterclockwise angles of rotation should preferably be set at a level lower than the elastic limit (at a level which will not subject the instrument to a torque / stress exceeding the elastic limit). The lower the angles of rotation the safer the procedure, as long as the instrument can still cut dentine, advance apically in the canal and remove the cutting debris in a coronal direction).

Question 30

summary of rct instrumentation

Answer 30

Use a method you are comfortable with and that you find predictable

Respect canal anatomy during shaping

Irrigation protocol is key

Aseptic technique (dental dam and use of hypochlorite)

Question 31

balanced force technique

Answer 31

60 degree clockwise rotation, maintaining apical preessure rotate anticlockwise at least 60 but not more than 120 degrees, repeating the cycle 3 times.

Question 32

reciprocation

Answer 32

a file working motion consisting of a counterclockwise (cutting direction) and a clockwise motion (release of the instrument) whereby the angle of the counter-clockwise direction is greater than the angle of the reverse direction

Question 33

patency filing

Answer 33

passing a small hand file thorugh the apical constriction and apical foramen to contact the apical tissues

Question 34

recapitulation

Answer 34

using a small hand file to ensure patency and dislodge debris into solution prior to introducing a larger file into the root canal system.

essential to prevent blockages or iatrogenic damage to canals,

Question 35

modified double flare technique

Answer 35

the process involves development of an initial coronal flare, followed by an apical flare.

these distinct regions of preparation, upon intersection create a continuous taper

preparation involves the use of Gate Glidden drills and stainless steel K-files

Question 36

watch winding

Answer 36

back and forward (clcokwise/anticlockwise) oscillation of 30 - 60 degrees, used with small diameter files

Question 37

filing

Answer 37

a dynamic movement of a hand file to optimally effect canal debridement; predominantly a push- pull (rasping), rotational (reaming) movement or a combination of the two. Engine-driven filing motions can be rotary, reciprocating or oscillating

Question 38

apical constriction

Answer 38

the apical portion of the root canal having the narrowest diameter; position may vary but is usually 0.5–1.0 mm short of the center of the apical foramen.

Question 39

apical foramen

Answer 39

main apical opening of the root canal

Question 40

correct working length

Answer 40

the distance in mm from a known coronal reference point to the position in the apical region of a tooth, where the endodontic preparation terminates, in most cases at the apical constriction.

Question 41

the most reliable way to calculate the correct working length (CWL) when instumentating a root canal is?

Answer 41

using an electronic apex locator (EAL) like the Morita dentaport