endo # 10 -Tamara Mosa

Endo lecture (21/11/2010)

In the previous lecture we discussed:
1-(root canal preparation) in other words root canal cleaning and shaping .
2- The goals of root canal treatment in endodontic treatment
3-The techniques of root canal preparation and they are more than one technique but our focus was on the (step back) technique

** The goal of root canal treatment is the prevention of periradicular disease or the treatment of this disease if it already exists **

In root canal treatment we depend on the chemo-mechanical debridement (chemical component + mechanical component)
The chemical component: which depends basically on cold irrigation using sodium hypochlorite (commonly known as Clorox) which is the irrigant of choice and the purpose of its use is cleaning the canal!
The mechanical component: which is the instrumentation or shaping of the canal, the main purpose is to allow deep irrigation or deep cleaning of the canal in order to permit the canal to receive the 3 dimensional root canal filling.

The mechanical objectives of root canal treatment are summarized in:
1- obtaining the shape that we want which is continuous tapering of the canal where the widest diameter is located coronally and the narrowest diameter is located apically, also we have to achieve the concept of flow, so the shape of the canal has to be conical in a smooth way (انسيابي) in order to permit good root canal root canal filling in its 3 dimensions.
2-Most importantly we have to maintain the original shape of the canal ,we have to widen the canal, but we have to preserve the original shape of the canal ,so if the canal was curved we have to maintain the curvature of this canal (we do not straighten it)
3- We have to maintain the integrity of the apical part of the canal (apical foramen) by doing:
A) The step back technique by what’s called (recapitulation) >>in which we re-insert the master apical file to the full working length so that we prevent any type of blockage or any collection of debris apically.
B) Apical patency process >>which is the re-insertion of a very small file (8 or 10) 0.5 mm beyond the working length in order to make sure that there is no debris inside the apical canal ,and by doing so we are preserving the integrity of the apical third of the root which is the most delicate part of the canal .
So as we said there are so many techniques but the one we’ll be taught is the step back technique , but it’s not the only technique ,there are more than 40 techniques for root canal preparation but the step back technique is the most widely used and taught before there was introduction of rotary instruments in the recent time.
Basically the strategies for root canal preparation are divided into 2 approaches:
1- The coronal-apical approach
2- The apical-coronal approach

Working length: it is the distance measured from the (occlusal surface, cusp tip, incisal edge) to the apical constriction which we estimated radiographically (1 mm short of the radiographic apex), but we can measure it accurately using the apex locater
The 3 components of the step back technique are:
1- Apical preparation : ( this step is done after measuring the working length)
In this step we prepare the most apical part of the canal ,we start with small files (15 then 20 then 25 then 30 ) because the canal is small , until we reach what’s called the master apical file at the full working length .
(Master apical file: It is the largest file to be used to the full working length)
Q: How do we know which size is the master apical file????
A: it depends on the tooth and root canal anatomy , if we have an anterior tooth (upper central or upper canine) with a wide and straight canal ,it differs from the MB “mesiobuccal” canal of the upper molars “1st and 2nd” or lower molars”1st and 2nd” >>> because the MB canal is a curved, fine canal.
But as a rule: the 1st file that binds at working length you have to go at least 2-3 sizes bigger. >>> So if the 20 file (بدقر) then you go (25, 30, 35) at the full working length.
So in this 1st stage we start with file 10 and make a filing action (up and down action) with 1-2 mm amplitude then we insert a larger file (15)
Note: WE HAVE TO MEASURE THE WORKING LENGTH BEFORE DOING ANYTHING!
So after file 10 we use file 15 which is white in color then we use the files 20 and 25!
(Memorize the color coding)
If we have a curved or fine canal it’s ok to end with file 25 !

The outcomes of this step:
1-open apex: which is WRONG, because then we won’t be able to confine our instruments or our irrigation to the root canal system and they’ll spill out and cause irritation and inflammation of the periodontium which contradicts with the main goal of our treatment (prevention and cure of periradicular disease)
2-Apical seat : we have a resistant or resistance form and a constriction and a funnel shape
3-we have what’s called an (apical stop) “عتبة” at the full working length
***Both 2 and 3 are acceptable apical preparations
But how do differentiate between them?
In the apical seat there is a some sort of narrowing, if you insert any file 2-3 sizes smaller than the master apical file it will pass because the canal is narrower!
In the apical stop if you try to insert an instrument 1-2 sizes smaller than the master apical file, it will stop (will not pass)

We have to maintain the original anatomy of the canal in order to avoid perforation as we see in the picture in the slides (which unfortunately I don’t have), this perforation will cause irritation and inflammation of the periodontium.
(We have to work carefully to avoid iatrogenic dentistry >>
الطبيب عن تنتج التي الأخطاء
So you have to irrigate between each instrument using adequate volume of sodium hypochlorite, because mechanical instrumentation alone can’t reach inaccessible areas in the complex anatomy of the tooth such as:
1-lateral canals
2-furcational canals
3-accessory canals
4-inter-canal communications
5-communications between pulp and dentine through dentinal tubules (organisms can penetrate inside the dentinal tubules, so irrigation can follow them anywhere they are)
NEVER WORK IN A DRY CANAL 
(mechanical instrumentation by an expert won’t take more than few minutes but the problem is in spending at least half an hour of irrigation, that’s why root canal treatment needs time because the amount of irrigant that reaches the fine canals is not enough for the irrigant to perform its work so you have to be patient and spend time to allow enough amounts of irrigant to enter, experts finish root canal treatment in 30-40 minutes in one visit)
The most important characteristics of sodium hypochlorite are:
1- An antimicrobial ,antibacterial
2- Dissolves organic debris (pulpal tissue)
Other things can be done by any other irrigant such as lubrication and flushing out of debris.
Note: never force sodium hypochlorite irrigation beyond the foramen in order to avoid very painful and bad results.
There are other forms of lubrication like EDTA (ethylene/diamine/tetra acetic acid)
Such error can be repaired within 2 days using analgesics (steroidal, non-steroidal)

So the first step is apical preparation and we reached the size that we want which is 25, now, this is not enough for us to say we obtained a clean, wide canal, because the canal is narrower apically in diameter and it widens coronally >>this is the idea behind the step back technique, that we benefit from the flexible files in preparing the apical part of the canal and stepping back using bigger files that are stiffer to prepare the wider part of the canal
[[If we use these larger and stiffer files in the narrow part of the canal at the working length, we’ll end up with so many problems like alteration in the anatomy of the canal, or perforations]]
In this technique we reduce 1 mm of the working length and use a bigger file, reduce another 1mm of working length and use a bigger file, and so on
This technique is in harmony with the original anatomy of the canal, but what we fear, that by creating such steps there’ll be collection of debris, and to avoid such thing we perform (recapitulation) > whenever we go a step 1 mm short of the working length we return with the master apical file (or with a file one size smaller than the master apical file) to the full working length in order to disintegrate any debris that has accumulated below and flush it with irrigation.

Another concept is the apical patency:
It is to insert a file that’s smaller (8 or 10) 0.5 mm beyond the working length to ensure that the apical canal or foramen is patent >>to preserve the integrity of the apical part of the canal and avoid any apical blockage
Now we are done with the stepping back, we are now in the coronal part, here we do (coronal flaring) by using Gates Glidden drills size (2, 3, and 4)
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Size 1 is very small, very flexible and can fracture easily
Size 5 is very big, can cause over weakening and over destruction of the tooth
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Size 2 can be used 6 mm inside the canal
Size 3 can be used 4 mm inside the canal or below the orifice
Size 4 can be used 2 mm below the orifice
So we get our continuously tapering canal with the narrowest diameter apically and the largest diameter coronally

What are the criteria that we should consider to know if our preparation is adequate?
1- The spreader should ideally reach 0-1 mm short of the working length this will ensure a good apical seal and taper (spreader : it is a tool that looks just like a file but with no cutting edges ,it’s used in the root filling procedure in what’s known as the lateral condensation technique)
2- Canal walls should feel smooth, hard
3- Clean dentine filing (we don’t see rotten and very soft stuff)
4- Good apical stop
Q: how do we check our taper??
A: by using the spreader
Then we dry the canal and it’ll be ready to receive the filling.
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Between the visits you have to put a very good coronal restoration or a temporary restoration that’s strong enough to stay in its place ‘till the 2nd visit, because if we don’t have a good coronal seal the whole treatment will be ruined 
Sometimes we place an (inside canal dressing) called (unsetting calcium hydroxide) which is injectable OR we can use a DRY cotton pellet.
NOTE: it’s contraindicated to use a cotton with cresol because cresol is toxic and of no benefit.
The step back technique is not the best technique, it has limitations, also has the tendency to straighten the canal , and debris frequently collects at the apical region and either becomes extruded through the apex or blocks the canal
Since the curvature of the canal is reduced during mid-root flaring there’ll be loss in the working length, the magnitude of which is variable .
When we measure the working length then use this technique the canal will straighten a little bit ,there’ll be a loss in the curvature so the true length of the canal will be less than the one we measured in the beginning >>so there is this tendency for over instrumentation or instrumentation beyond the apex .
[[Modifications were done to this technique and gave rise to “passive step back technique” which will be given to us with the handout]]

The 2nd approach (coronal-apical approach):
Advantages:
1- Most microorganisms will be in the coronal third of the root canal system
2- Better access to the root canal so that we allow the irrigant to reach even deeper inside the canal
3- Working length is less likely to be altered
4- Better penetration of irrigation

The step back and step down techniques are very similar:
In both we start with making the access cavity then locating and checking the patency of the canals
But :
*In step back technique we measure the working length then we perform the rest of the procedure (apical preparation, stepping back, coronal and mid-root preparation)
*In step down technique after locating the canals and checking their patency we make coronal and mid-root preparation then we measure the working length .>> so that any straightening in the canal will be before measuring the working length so the working length will NOT change .
Again: we make coronal and mid-root preparation (which is the straight part of the canal if it was a curved one) THEN we determine the working length followed by apical preparation and then stepping back.
So the difference between the two techniques is WHEN we obtain the measurement of the working length.
(Other techniques were just mentioned: modified double flare technique, balanced force technique)
So many errors are due to the complex anatomy of the root canal
In the slides there is a picture of a resin model of a real root canal anatomy
Most common errors are in the small curved and long canals
In apical preparation the normal situation is to maintain the original anatomy of the canal
Again in the slides in picture B the file is stiff
((all instruments are stiff and all canals are curved >>this is our assumption ALWAYS))
So the stiff instrument will tend to cut from the apical part of the root leading to what’s called (apical transportation) which is moving the apex from one place to another, also known as the production of a (reverse funnel) which is very difficult to fill and seal and we can end with perforating the canal and finally with apical zipping >>all this is due to the use of a large stiff file in fine curved root canals
In the slides the picture resembles an upper premolar >>we have to consider all roots are curved even if they appeared straight in the radiograph.
So stiff and large files have the tendency to straighten inside the canal and cut from the outside dentine instead of the inside dentine leading to zipping and perforations in the side of the root
In the slides there is a picture that looks like an hourglass or an elbow >> in this case the file tends to straighten inside the canal so it cuts more from one side and less from the other (cuts in the coronal part of the canal from the outer curvature whereas in the apical part it cuts from the inner curvature) >>>>>> so an (hourglass, elbow) shape forms, which is very difficult to fill.
Zipping: is the tendency of the file to straighten inside the canal, resulting in the over enlargement of the canal along the outer side curvature, and under preparation of the inner aspect of the curvature
Elbow: imbalanced cutting and irregular widening, coronally along the inner aspect and apically along the outer aspect.
So this irregular shape and insufficient taper and flow may jeopardize the cleaning and the filling of the apical part of the canal, ledging of the root canal may occur due to the use of inflexible instrument in curved canals causing what’s known as a step or a ledge due to the lack of proper irrigation and manipulation of the instrument .
In this case it’s really hard to re-obtain our working length so this area will be inadequately prepared and filled, jeopardizing our treatment
In the picture the doctor insisted on re-obtaining the working length with a screwing action using a stiff file >>he perforated to the root
The cause of a ledge is:
1- inadequate straight line access ,
2- filing of the root canal short of the working length ,
3- over enlargement of small curved canals
4- Loss of patency by debris packed inside the canal
5- The use of larger files
NEVER use a large file to overcome a ledge!! EVER!
So we use the smallest files we have in our clinic (6 or 8 or 10) we create a little curve in them and try to bypass the ledge.

Anti-curvature techniques:
In the inner third of the root we have thin dentine (danger zone) while in the outer third we have thick dentine (safety zone)
So in curved canals we don’t make circumferential filing to all walls to the same degree, we make (anti curvature filing) which focuses on the safety zone (outer zone) more than the (inner zone)
In the picture an error made by a doctor caused the files to protrude from the root in all directions from the danger zone because he/she didn’t care about the thin dentine >>>strip perforation
Another picture shows us an over instrumentation in the furcational area that made the filling enter the periodontium

Apical blockage occurs when we don’t do recapitulation >>so if you left the canal for 2-3 minutes without recapitulation or irrigation or patency ,the debris will solidify and you won’t be able to remove it ,then you have to extract the tooth 
We have to avoid fracturing our instruments that’s why it’s important to know their physical properties and the limitations .
ALWAYS: prevention is better than cure
Do it right from the 1st time
Throw away any deformed tools

Files in modern countries are used only once because of:
1- The deformity that occurs in them
2- Cross-infection control

CONCLUSIONS:
*The successful outcomes of root canal therapy depends on good preparation (cleaning and shaping)
*Remove any agent that causes periapical inflammation .
*complete cleaning and shaping (not the whole treatment) in one visit if possible to prevent swelling >>if you were very busy you can do your access cavity and send the patient home.
*coronal followed by apical preparation is better
*keep instruments within root canal and avoid extrusion to the periapical tissue
*instruments should be used sequentially
*the prepared canal should include the original canal not straightened, not transported, and should end with apical narrowing, and tapering smoothly from crown to apex (concept of flow)
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Done by: Tamara Madhat Mousa
A special hi to Lana ,halah and to their new family member George (kholeo) the turtle and to,muna and lama ,and to all the true people out there .
\m/