With manual files: smoothen canal
walls, create glide path then introduce your rotary file.
The goal is to obtain smooth wall
and maintain this smooth wall.
Importance of glide path:
Decrease fracture of files.
Saves anatomy.
Gives you a 3D idea about the
internal anatomy of the canal through the shape of the file. When you introduce
the file into the canal till the w.l then remove it in up & down motion
without rotation, it directs you to the curves inside, as if you’re taking an
impression to the canal.
Glide path is done with file 10
and maximum 15.
Apical transportation is a fatal
mistake that may happen due to sudden size transmission (from 10 to 15), so, in
severe cases use an intermediate file (12.5) after 10. This is called micro
glide path.
Macro glide path is done using
flexible Ni-Ti instruments 15 & 20.
You’ve to maintain patency
between files.
2)Shaping:
The previous steps were just
preparation for shaping.
During shaping, we have fear of
files separation.
We’ve 2 mechanisms of fracture:
Cyclic fatigue (with large
instruments and repeated use).
Torsional overloading (in narrow
canals when the file become locked).
To overcome cyclic fatigue:
change motion or change metallurgy.
Motions:
Continuous rotation.
Reciprocation: it’s not recent in
endodontics, but recent in rotary systems. It increases fatigue resistance.
Alternate reciprocation (same as
watch-winding).
Rotating reciprocation: 90
degrees CW and 30 degrees CCW (wave one gold and reciproc). There’s no single
file system for canal preparation, single file can be only for canal shaping or
enlargement part, but you’ll need manual files for glide path and patency.
Combined motion: in TF adaptive
file, when it meets resistance, it turns from continuous rotation to
reciprocating rotation.
OTR / OGP (optimum torque
reduction / optimum glide path): Alternate reciprocation, it rotates CW and CCW
at the same degrees, when it meets resistance, it turns into rotating
reciprocation.
Metallurgy:
Before 2008, all Ni-Ti were
nitinol which had unpredictable fracture.
They were then heat treated to
transform them from austenitic phase to martensitic phase which can withstand
bending and has high cyclic fatigue resistance. That’s the M-wire (protaper
next files).
R-phase files (such as TF or
K3XF) are thermo-processed to reach a phase between austenitic and martensitic,
it also withstands extreme bending.
Controlled memory files (CM files):
shape memory of Ni-Ti files put a lot of pressure on the file inside the canal,
it may lead to transportation, because it cuts through the outer side of the
curve more than the inner side. That was overcome with CM files such as
hy-flex. Proceed it inside the canal (inactive – static) until it meets resistance
then activate it, the file takes the same curve as the canal and never makes
transportation.
Protaper gold: it’s not
controlled memory but decreased shape memory files.
To overcome torsional
overloading: there shouldn’t be total frictional fit between file and
canal. To avoid:
Coronal apical technique.
Less vertical force & torque.
Less stress on files.
3)Precautions for rotary files:
Pre-operative radiographs: gives
an idea about the curve, its radius and abruptness.
TTT planning before shaping.
Before using new files in a case,
you’ve to try it 1st on extracted teeth.
When the file is loaded with
debris its cutting efficiency is decreased, then it should be removed, cleaned
and re-introduced into the canal.
The rotary file should be
inspected before, during and after use. Any bent, shiny spot or permanent
deformity within the file indicates that it needs to be discarded.
You’ve to make brushing action
after finishing shaping because the canal is always oval not round.
Whenever you reach the reference
point, retract your hand-piece, because if the file kept rotating it will break
the apical stop.
The time a file should spend
inside a canal is 5-10 seconds maximum.
4)Selection of last file & irrigation:
Objectives of shaping:
Mechanical
cleaning: visual gauging: inspect by your
eyes that you touched all canal walls, you should see clear white dentin chips
at least in the apical 3 mm of the file.
Irrigation:
I need my irrigant to reach 2 mm
before working length to be effective.
Type of irrigant: NaOCl is the
best to be used + chelating agent and the delivery system.
NaOCl half concentration is
preferred over full concentration because of less toxicity and side effects.
Passive irrigation: luer lok
plastic syringe is used. Needles must be side-vented because end-vented ones
cause NaOCl accident.
Active irrigation: by ultrasonic.
Final irrigation protocol: 3-5 minutes’
irrigation for each canal. Drop of NaOCl for 30 seconds, I give time for
chlorine ions to work on dissolving pulp tissue, then flushing by saline to put
EDTA. If I put EDTA immediately on NaOCl, it decreases its effect and action.
Obturation:
Bioceramic material is
hydrophilic and follows wetness of canals and fills them, given you’ve made
good and efficient irrigation.
Biominimalism concept: once you
feel that you can obturate and your canals are cleaned don’t overcut and
enlarge more.
Final finishing file depends on
your ability to clean and obturate.
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