instrumentation of the root canal system Flashcards
chemo(bio) mechanical preparation
Chemo =
Irrigate to kill micro
Organisms
Remove smear layer
Mechanical =
Prepare shape
Flush out
chemomechanical aim
Shape the canal
Allows delivery of sodium hypochlorite to working length
Creates shape to obturate
challenges of RCT prep
root canal system is very complex
number, length, curvature and diameter of canals can vary considerably
vertucci classification
teeth are weird
design objective
creating a continuous tapering funnel shape
maintain apical foramen
keep apical opening as small as possible
estimated working length
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.
corrected working length
Length at which instrumentation and subsequent obturation should be limited
Obtained by the use of an electronic apex locator and/or working length radiograph.
master apical file
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
types of rct motion
Filing
Reaming ( warning)
Watch-winding
Balanced Forced Motion
Envelope of Motion
watch winding
back and forward of 30-60 degrees
light apical pressure
effective with k files
useful for passing small files
balanced force
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
initiate irrigation protocol
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.
barbed broach
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
iso colour code
white = 15 45
yellow = 20 50
red = 25 50
blue = 30 60
green = 35 70
black = 40 80
stainless steel instruments
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
hedström Files
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
reamer
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
k-files
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
nickel-titanium
developed in 1960s for space program
Nitinol - Nickel Titanium Naval Ordnance Lab
shape memory effect after heat treatment
SUPERELASTICITY
components of an endodontic rotary instrument
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
superelasticity
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
advantages of NiTi versus SS
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
disadvantages
instrument fracture
expense
access can be difficult in posterior teeth
unsuitable for complex canal anatomy
pro taper hand use
S1 -> S2 -> Sx
or F - finishing files = good for large files
rotary instrumentation
guidelines:
straight line access
cross-sectional diameter
root canal system anatomy
speed and sequencing
lubrication and a “light touch”
creating a glide path
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)
when using rotary
remember to clean the debris
irritate
make sure canal is free to 1m beyond the prepared canal section
files are one use only because
of prion decontamination
instrument separation
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
cyclic fatigue
free rotation in a curvature
generation of tension/compression cycles
cyclic fatigue
failure
torsional fatigue
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).
summary of rct instrumentation
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)
balanced force technique
60 degree clockwise rotation, maintaining apical preessure rotate anticlockwise at least 60 but not more than 120 degrees, repeating the cycle 3 times.
reciprocation
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
patency filing
passing a small hand file thorugh the apical constriction and apical foramen to contact the apical tissues
recapitulation
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,
modified double flare technique
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
watch winding
back and forward (clcokwise/anticlockwise) oscillation of 30 - 60 degrees, used with small diameter files
filing
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
apical constriction
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.
apical foramen
main apical opening of the root canal
correct working length
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.
the most reliable way to calculate the correct working length (CWL) when instumentating a root canal is?
using an electronic apex locator (EAL) like the Morita dentaport
