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we

6

Amr Msameh

Dr. Ahmad El-Ma’aita

…

Heba Redwan

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****the doctor went through the lecture in different order than the

slides, PLEASE refer to the slides for proper order of steps.

In the lab we are learning the skill of how to do a root canal treatment

but we should also understand the purpose & objectives of doing these

certain measurements.

Today we’ll be talking about Mechanical instrumentation:

a- Definitions

b- The chemo-mechanical instrumentation concept.

c- Hand instrumentation:

1- instrumentation motions:

Reaming, filing, watch winding, balanced force, anti-curvature filing

2- Techniques:

The step-back technique.

The crown-down technique.

Hybrid techniques.

d- Rotary instrumentation.

e- The smear layer.

f- Procedural errors during canal instrumentation.

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The next figure demonstrates the basics of RCT which is composed of:

1-chemo-mechanical disinfection:

A-Mechanical instrumentation, which is what we are going to

be talking about today and what we are going to be practicing

in the lab (the step-back technique).

B-Irrigation with chemicals: what we use to wash the canal.

C-Inter-appointment medication: we use it sometimes

2- Fluid-tight seal:

a-root canal obturation: how to seal the canal it self

b-Coronal seal

If any of these steps are done inappropriately, with the exception of the

inter-appointment medication because we don’t always need it, the

treatment will be a defecated.

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Debridement

is basically the

elimination of the

infection, so we start

with the mechanical

instrumentation to

scrape of bulk of the

infection which is

mainly caused by

bacteria that has the

ability to create its own

community called

“Biofilm” with time and

the right environment, biofilms are very difficult to get rid of that’s why

we have carries, gingivitis & periodontitis resulting from the plaque

which is a biofilm on the tooth contour.

Think of it as a dirty cocking pot, we first use a sponge to scrape off the

bulk of the dirt but that’s not enough to make it shinny and clean again

we need to use some cleaning agent (chemicals) to clean it properly.

Objectives of mechanical instrumentation:

1- Eliminate microorganisms from the root canal system

2- Remove pulp remnants and organic debris which provide a

substrate for microbes.

3- Remove the superficial infected layer of radicular dentine.

4- Shape the canal in a way to facilitate the access of irrigating

solutions and medicaments and the placement of a well compacted

root canal filling.

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The ideal canal preparation:

1- The canal must remain in its original position (the canal isn’t a

straight line it’s a curved line from the tip of the root to the crown

so we want to maintain this shape and only enlarge it but not to

create our own canal).

2- The apical foramen which is where the root canal exists the root,

must remain at its original location and size.

3- The canal must resemble a tapered funnel and be kept as small as

is practical. (tapered shape: a shape that increase in diameter

throughout its length.)

4- The preparation should resemble a tapering funnel.

While we are doing the mechanical instrumentation we’re washing out

the debris and whatever comes out with a solution, so the following are

the objectives of the chemical disinfection:

1- To flush out remnants of pulp tissue and debris created during

mechanical instrumentation (any liquid even tap water has the

ability to flush out the debris that come out as we are cutting the

canal walls but other properties are needed in the solution such as

the next point).

2- To dissolve residual pulp tissue.

3- To kill microbes and remove microbial biofilm.

4- To clean the parts of the root canal that are inaccessible to

mechanical instrumentation (eg: isthmi, lateral canals... Etc.).

5- Facilitate instrumentation by acting as a lubricant.

6- To remove the smear layer.

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If we take an x-ray for a tooth that’s infected, we’ll see

a shadow around the root, that is the result of:

• Most of the time its carries reaching deep in the

dentine thus toxins will start to irritate the pulp

that will react by a certain extend by

inflammation “pulpitis”

• unlike inflammation in other places in the body

where we can find the five sings of inflammation

(pain, swelling, redness, hotness and lose of function) those signs

don’t occur inside the pulp because the pulp in contained in a hard

tissue it does not swell, so the extracellular pressure increases as a

result of the increased vascularity caused by the inflammation, thus

preventing the venous backflow so the pulp becomes ischemic then

necrotic, when the pulp becomes necrotic there’s nothing we can

do to stop the progress of the infection inside the root canal

system.

• When the infection reaches the apex of the

tooth it tries to escape into the body, so the

body tries to stop the progress of the

infection, by another inflammatory reaction

but this time it’s not called pulpitis it’s called

“Apical periodontitis” as part of this

inflammatory process the body is sending

WBC & osteoclasts to the area resulting to

resorption of the bone by osteoclast and

deposit granulation tissue .

If we give this process a lot of time, significant portion of the bone

will be resorbed and replaced by granulation tissue, so when we take

an x-ray depending on the difference in radio opacity this shadow will

appear around the root because the granulation tissue isn’t as opaque

as bone thus we can use this as an indication that the tooth has been

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infected, in this case we have two treatments either extracting the

tooth or preform RCT(get rid of the infection, kill the defection inside

the tooth, then give it a good seal) so in the 2nd x-ray we can see that

after preforming RCT bone regenerated around the tooth after a

period of time.

Going back to Taper, this figure illustrates a taper

shape we can see that it’s diameter changes throughout its

length, (we will be asked about it in this year and

fallowing years), so the diameter at the tip of the taper is

0.4mm then if we move upwards or coronally 1mm in

length the diameter will increase becoming 0.45mm and if we move

another 1mm the diameter will increase becoming 0.5mm and

so, so the taper changes in diameter 0.05mm for every 1mm of

length, 0.05 is 5% so this is a 5% taper ( 𝛥𝐷

𝛥𝐿%).

Why do we need a tapered canal

preparation?

1- To facilitate the flow of irrigants in the canal (so

that the fluid can reach the apex of the root and

get out, the bigger the taper the easier it’s for the fluid to get in and

out (10% taper) while it’s so difficult in a straight cylinder, but

bigger taper means we’re cutting excess of the tooth structure so we

will have to settle for something in the middle 5%)

0.5 mm

0.45mm

0.4mm

0.00 Taper

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2- To reduce the stress on the instrument during instrumentation

(because we don’t want the instruments to touch the canal walls all

the way, instead we want them touching certain parts of tooth).

3- To facilitate obturation and the placement of inter-appointment

medication.

Hand instrument:

• K files:

the most standard file and everything else is a variation of it

o its active part is the tip upward including the rough part & it’s

called the working part, its length is 16 mm which is standardized,

it’s made of a block of metal with a square or triangular base that’s

then twisted a certain number of times per unit of length thus

producing warps (the spiral lines along the working part *the doctor

used the word flutes which roughly means not following a rule*),

those flutes have a cutting act as they move across a surface,

o the file also has handle

which is color coded

according to size.

o a rubber stopper that help

us measure length

o a shank connecting the

handle with the working

part.

So they come in different sizes

that are color coded and each

size comes in different lengths

(the working part is standardized but the whole length of the file

varies) so if you are working on a posterior tooth you most likely need

a short file 20 mm, the standard is 25mm and there are long files up to

31mm.

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Q: size 30 K file means the tip of the file has a diameter of 0.3mm, so if

we moved 2mm away from the tip, what would the diameter be?

to solve this question, you have to remember that All K files have a

standard taper of 2% which means the file increases in diameter 0.02mm

for every 1mm of length, so the answer is 0.34 mm

Small sizes files are squared

(originally the metal block

had a square base) and

larger files are triangular.

The smallest file is

size 6 file (tip

0.06mm) which is

pink, then size 8

which is grey, then

size 10 which is

purple those 3 files

are the exception because after that the color code becomes white

→ yellow → red →blue → green → black,

with 0.05mm change in diameter between each color, this cycle is

repeated and so on meaning a red file could be either size 25, 55 or

85. (each size for each color is 30 sizes bigger).

The following mnemonic would be helpful for memorizing colors order

(Why You Read Before Going Bed)

and if you’re confused about the two B’s, remember (start with white,

end with black)

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• Gates Glidden drills: they are

side cutting drills, they are very

useful for coronal flaring, they

are made of stainless steel, sizes

1-6 according to the number of

bands on the shank.

Mechanical steps of root canal treatment:

1. Access cavity preparation (in the lab we are being trained to do a

conventional access cavity, keep in mind that in clinic we do carries

removal first and once we have a carries free tooth structure we assess

whether the tooth is restorable or not, thus preforming RCT without

drilling a new surface we just extend the cavity that we already made).

2. Working length determination. (we have certain devices to determine

the length, we can use x-rays or tactile sensation)

3. Canal instrumentation (cleaning and shaping) (chemo-mechanical

disinfection)

4. Obturation of the

prepared root canals.

5. Provision of coronal seal.

No matter how good you are in the first 4 steps; if you don’t seal

properly and coronal leakage occurs the tooth will get reinfected.

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Basic instrumentation motions:

A-Filing motion:

-A linear motion with push and pull action with effective

action during pulling. It aims to scrape the canal wall. Also

known as rasping motion.

-The most effective cutting motion especially with H-files.

-Can pack debris apically which can block the canal or be

pushed out of the apex.

B- Reaming motion:

-A clockwise, cutting rotation of the file.

-Instrument is inserted into the canal until binding is

encountered. Then It is rotated clockwise 180-360º and

pulled out.

Although we call them files but actually, we use the hand files as

reamers, the difference is that in filing we do an up and down

movement (up and down straight strokes) but if we do this with a

file:

A. It’s more aggressive because the canal isn’t straight, we are

working on a curved canal, so by using filing we are acting more on

the outer wall of the curvature. (the wall opposite to direction of

curvature).

B. The debris that is created by filing (the in and out movement) is

getting packed inside the canal and getting pushed it toward the

periodontal tissues causing abscess or it may block the canal.

So, filing motion is not encouraged, although it’s the fastest way to

widen a canal but it has a bigger likelihood to errors.

Reaming motion is composed of twisting and pulling, advancing the file

while twisting it, files are designed to engage dentine in a clockwise

twisting and disengage in a counter-clockwise motion.

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c- Watch winding motion:

-A reciprocating back and forth (clockwise/counterclockwise) rotation of

the instrument in the canal. (clockwise then pull out by the twisting

counter clockwise, if we keep twisting the file clockwise it’ll bind inside

the canal, after that if we keep twisting it’ll snap and break).

-Light apical pressure is applied to move the file deeper into the canal.

d- Balanced force technique:

-it’s basically rotating the file certain degrees (180⁰ degrees according to

Rowan “the one who has discovered this technique”) clockwise then (360⁰)

counter-clockwise while maintaining pressure, the idea is to engage

dentine then disengage dentine while maintaining file position

-advantages: remaining central in the canal, being conservative to tooth

structure.

*these first 2 points is how

the doctor described the

technique it differs in the

numbers but the same

concept from the slides*

-Allows controlled

manipulation of hand files

whilst maintaining a centered preparation and reducing the incidence of

procedural errors.

-The file is inserted in the canal until resistance is met and rotated 90°

clockwise to engage dentine in its flutes.

-The file is then rotated 180° counterclockwise whilst maintaining apical

pressure. This action cuts dentine from the canal wall and is associated -

with a characteristic click.

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-A further clockwise rotation collects debris on the flutes before being

withdrawn from the canal.

e- Anti-curvature filing:

-it’s a concept more than a technique, it’s main idea is to

avoid strip-perforation (which is perforation of the inside

canal wall –the wall that is with the curvature as it’s

thinner than the outside wall-), so we do anti-curvature

filling meaning filling more on the outside wall and less

on the inside wall.

-The controlled and directed preparation

into the bulky or safety zones and away

from the thinner portions or danger zones

of the root structure where perforation or

stripping of the canal walls can occur.

-A concept described by Abou Rass in

1981.

Hand instrumentation techniques:

▪ Standardized technique (entering with whatever file suites the canal

then increasing the file size gradually, till you reach the desired canal

size for e.g if we enter a size 30 file the last we’ll end up with a canal of

0.30 mm in diameter and since all files are standardized to 2% taper then

the canal will also be a 2% taper)

▪ Step-back technique (it’s what we are going to use in the lab so we

need to understand it really good)

▪ Crown‐down technique (we can achieve this technique with hand file

but in our fifth year we will use rotary instruments and rotary

instruments are all about this technique)

▪ Hybrid techniques (any combination of any techniques because there is

no technique sufficient to all cases).

-Strip perforation

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The step-back

technique,

it’s basically that after determining

the working length of the canal,

(remember that my goal is to

eliminate the infection which

includes the inner part of the canal

walls that contain the biofilm stuck

on them, I want to create room for

my irrigant to reach the apex

because if it doesn’t reach the apex

we won’t eliminate the infection, &

we want to create a shape of the

canal that is easy to operate)

then I reach the apical constriction by trying

out files starting from the smallest and going

bigger until I reach what is known as the

initial binding file which the first file that

binds to the apical part so for e.g if we start

with 15 then 20 then 25, and at 25 we felt

some resistance at the apex thus 25 is the initial

binding file,

then in order to clean the apical part we go three

sizes larger, so we use size 40 file to reach the full

working length so this is called the master apical

file which is the largest file that reach the full

working length.

step-back technique

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When we start with coronal flaring

we use gates gliddens (size 2, 3 & 4 and

that’s it) the idea is:

1. create the funnel shape by

widening the radius to create

a reservoir for the irrigant,

thus every file that ente0072

inside the canal will first pass

through this reservoir of

irrigant.

2. To reduce stress on the

instrument (by making the

instrument working and

engaging only on the apical

and middle part of the canal

rather than working on both

coronal, middle & apical

parts).

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3. To remove the bulk of the infection coronally instead of pushing the

infection from the coronal part to the apex, this will help reduce the

infection.

After doing coronal flaring, we try the files –let’s continue the

example that 25 file is the initial binding file, thus size 40 file is the

master apical file-

from now on we will increase the file size for every 1 mm of length;

(1mm increment, it’s not actually fixed you will determine the

increment according to the shape of the canal you want to achieve)

so size40 is the MAF, then we will go with size 45 file for a certain

length that equals ( the working length minus 1mm, L=W.L - 1mm)

after that size 50 which is 2mm shorter than the working length, then

55’ 3mm short then 60 ‘4 mm short and so on…

if you look at the figure(go back to page 14) you can see that we are creating

steps that’s why it’s called the step-back technique because we are

taking one step backward every single time,

between each step we go with the master apical file and round the

edges to achieve a taper canal this is called Refining phase in the

example we achieved a 5% taper because in every 1mm going

upward the diameter increased 0.05mm, whereas if we wanted to

achieve a 10% taper we change the change in length for each step

instead of 1mm we make it 0.5 mm (thus the change in diameter for

every 0.5 mm will be 0.05mm → change in diameter for every 1mm

in length will be 0.10mm → 10% taper) or we can manipulate the

change in diameter which is easier (instead of using the 45 file after

the 40, we use size 50 file while keeping the change in length

constant 1mm), in long teeth such canine a 5% taper might be too

aggressive (which means achieving will cut a lot of the tooth

structure) so we might go with a 2.5% taper (it can be achieved by

making the change in length 2 mm and keeping the file size step

constant and equal to 5 -45 then 50 and so on-).

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To make sure that we achieve a 1mm change in length we use the rubber

stopper and assign the desired length (for the 1st file after the master

apical file its 1mm shorter than the working length and so) then we start

instrumenting the canal by watch wind motion till we reach the desired

length without any resistance.

Recapitulation, is simply going the

full working length with the master file

after each step to grind the rough edges

thus achieving taper and to make sure

that there is no packing debris.

patency filing is a controversial

technique, by definition it is going with

the smallest file you have (usually size

10) beyond the working length through

the apex to ensure patency (patency

means open ,so ensure that the canal

isn’t blocked), it’s controversial

because we are pushing stuff toward the

periodontal tissue because this might cause

acute flare (pain) and we might push the

infection also toward the periodontal tissue but

on the other hand if we don’t do patency filing

then we can’t make sure that debris isn’t

packed in the area between the apical

constriction and the apical foreman where the

body can’t deal with the infection thus causing a constant cause of

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irritation, recent studies suggest doing patency when the tooth is infected

and if the pulp is vital don’t.

crown down technique is opposite to the step back technique so instead

of preparing the canal from apex upward, you can start with a large file

cleaning the canal coronally and going all the way to the apex or

manipulating tapers by using large taper coronally then going downward

until reaching the apex.

`

Most rotary systems are based on the crown down

technique.

Rotary systems are basically files that fit on the hand

piece, the doctor opinion is that we should learn

hand filing as a primary skill because there is nothing we can do with

a rotary system that can’t be done by hand, but there is a lot that we

can do by hand that we can’t do by the rotary systems.

0.08

taper

0.06

taper

0.04

taper

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The smear layer, if you are

operating on a canal every time

you go in and out with your files

you are creating debris and this

debris is suspended with fluid, so

this debris is creating a layer

called the smear layer which is

made of pulp remnants, bacteria,

dentine chips and a lot more, this

layer has many effects on a RCT:

1. It prevents the irrigant from entering the dentinotubules and

cleaning them from the inside.

2. It prevents the seal from penetrating & binding to the

dentinotubules.

3. It may contain infection as it’s remnants of everything.

We have to remove the smear layer if the tooth was infected we remove

it by irrigation of 2 different solvents, one of them has the ability to

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dissolve organic substances (NaOCL) and the other has the ability to

dissolve inorganic substances (EDTA or citric acid).

Instrumentation related

errors:

those errors happen when

we use large intsruments

without respecting the

curvture of the canal, so the

file will go in a stright line

creating a ledge, we can

prevent a ledge by using

small files, but if we insist

on pushing the large file after it created a ledge it’ll creat it’s own path

or canal and this is what we call a zip or transportation and if we insist

further it’s going to create it’s own exist which is a perforation, a strip

perforation was explained earlier.

Shout to the monkey of the safeway, who was always there when we I needed a luagh, big love.