25-11-2013 Endo sheet # 9 Ali I. Al-Shara

Cleaning and Shaping

- This lecture will be like a discussion, because we already have some idea about it, and the main topic of it will be the cleanest and shaping of the root canal system.

- Why do we want to clean the canal? And from what we should clean it?

First, it might contain vital tissue which is severely inflamed or irreversibly inflamed in the case of irreversible pulpits.

Second, it might contain necrotic tissue, in order to remove any tissue that can provide a good medium for microorganism to live in.

Third, it might contain some microorganisms “bacteria, fungi, or viruses“, because when the pulp loses its vitality, it will be invaded by different type of microorganisms, which can come from the apex or from the lateral canals “accessory canals” in the case that we have a fracture in the root, and it loses its blood supply too, so we remove it and its byproducts.

- We want also to get the shape of the canal “shaping the canal”, why?

First, in order to be able to irrigate the canal in the proper way.

Because we depend in this case on the Chemo-mechanical Debridement method.

So we want to allow the irritant to penetrate deep inside the root canal system.

And as we saw in past few lectures, the root canal system is a complex structure, it’s not only the canals which we can see on the radiograph, because these canals can divide in a way we can’t see it in the radiograph, and there is a communication between these canals, also we have the accessory canals, also we have some inaccessible places for the mechanical cleaning, so we want the irritant to reach these places.

In the case we are professionals, we can allow the irritant to penetrate inside the dentinal tubules and it also helps to get rid of the microorganism that can go inside the dentinal tubules.

Second, in order to make a filling for the canal in the proper way.

Because if the canal was so small, there is no material could be placed in it, and couldn’t be condensed well, and it affects the density of the material, so we won’t get the perfect seal for the canal.

25-11-2013 Endo sheet # 9 Ali I. Al-Shara

- Why do we want to fill the canal?

Because if we didn’t do that, the microorganisms will enter the canal again, this will cause the re-infection of the root canal system. “The Hollow Tube Theory”.

- So now, when do the cleaning and shaping process, and the chemo-mechanical debridement we have some aim in our mind, and we should achieve them at the end of our work, and these aims are divided into two categories :

Category I = depending on the design “shaping of the canal”

Category II = depending on the biology “cleaning of the canal”

- Now we will discuss the first category of aims we have , which is related to the Design Objectives.

- What is the best Design we can do for the canal in order to get a proper irrigation and a proper filling without hurting the root canal system or the tissue surrounding the root?

1) To have TAPER of the canal:

- The original “natural” shape of the canal is to have a taper, i.e. the narrowest diameter of the canal will be in the apical third and the largest diameter will be at the canal orifice.

- So in order to maintain the original shape of the canal we have to do the same tapering of the canal, we don’t want to change the original anatomy of the canal, we should end up having the same taper or a little bit wider than the original one.

- So the first aim is to give a taper for the canal with a little bit larger than the original one, which allow the irritant and the filling to enter the canal.

2) The cross section of the canal should be the smallest in the apical area.

- Because when we when we talked about the apical constriction, we mentioned that it’s the narrowest diameter of the canal, and it acts as a natural barrier between the root canal system and the tissue surrounding the root “like the matrix in the class II amalgam filling”.

- So in order to have a matrix retainer to hold the filling of the canal, the narrowest diameter should be at the apical third, and we should preserve it.

25-11-2013 Endo sheet # 9 Ali I. Al-Shara

3) The root canal preparation should flow with the shape of the original canal.

- We have mentioned an important point in the first lecture, which is that all canals should be concerned curved, unless proved it’s straight, because it could be curved but we see it straight in the radiograph “remember, the radiograph is a two dimensional picture of a three dimensional object”.

- So the preparation should go with the curvature of the canal.

- So we use our instrument “whatever it manual or rotary” in the right way in order to maintain the original curvature of the canal.

4) The apical foramen should remain in its original position.

- The apical foramen is a highly sensitive area, because if we get over-instrumentation, or extrusion of the filling material, or extrusion of the irritant outside the apical area “toward the periodontium”, will we result in irritation of it and it will lead to inflammation in that area, and this is interfering with the main aim of the root canal treatment.

- So we should maintain the apical foramen as original as it is.

5) The apical opening should be kept as small as practical, not as small as possible, in the way which we can do the cleaning and filling process in the most proper way.

- Now, all things we have mentioned before is related to the Design Objectives

Again, as a revision, we talked about Tapering, Shaping, The maintenance of the apical foramen as small as practical, and The maintenance of the apical foramen in its original position and shape.

Question: how can we change the position of the apical foramen?

Answer: it’s done by our instrument, in the case of using very stiff instruments and we have round apical foramen, it may make it oval, and with our movement of the file it will keep pulling the foramen away from its original position.

- We have mentioned two important points,

The first, all canals should be considered curved unless proven otherwise.

25-11-2013 Endo sheet # 9 Ali I. Al-Shara

The second, the instrument we are using are not the ideal one, it should be considered stiff “except the small sized one 15, and 20 it have some flexibility”, and while we are increasing the size of the instrument it will become more stiffer, and it will have more tendency to straighten the canal, so they act to change the shape of the canal.

- Now, the second category of aims we have is the one which is related to the Biological Objectives.

- How can we do the instrumentation inside the root canal system? How to not forcing the necrotic debris beyond the foramen? “Because these particles a source of infection and irritation to the pulp”, How can we remove all organic tissue presented inside the root canal system? “Because if we left some remnant of it, it will be degraded and become nutrient for the microorganisms” How to make a sufficient space for the intracanal medicament?

- Intracanal Medicaments are something we use in order to clean the canal in the proper way “Remember the Chemo-mechanical Debridement Method”, and the most one we use is the sodium hypochlorite, there is some of them we use between the visits in order to give antibacterial effect, and to act as a physical barrier to close the canal, like the Non-Setting Calcium Hydroxide.

- Sodium hypochlorite:

We use 1-6% concentration of it.

Give two essential effects:

1- Antibacterial.

2- Tissue solvent, it dissolves the organic tissue inside the root canal system.

- We use a small side vented needle, in order not to force the intracanal medicament beyond the apical foramen and not to get a severe inflammation as a result of that.

“The side vented needle: is a needle which has an extra opening, in order to let the extra irritant to go outside the tooth”.

- In some cases of forcing sodium hypochlorite to go beyond the apical foramen, we may have Sodium Hypochlorite Accident, which is characterized by a severe inflammation of the face.

25-11-2013 Endo sheet # 9 Ali I. Al-Shara

We depend on the chemo-mechanical debridement method, because we all know that the root canal system is very complex.

And as we see in this picture, which present the root canal system that has been injected with ink, and this is the real presence of the communication in the root canal system.

By now, all objectives are clear in our mind.

- Now, we will concentrate on How to give shape to the canal?

- And about this thing we have a lot of manual techniques “ المبارد تحضيرات.the Filing method ”اليدوية

- In 1961, the standardized technique came out, because the standardization of the file came out in 1955 “they made the standards of color coded file, sizing, D0, D16, cutting segment … etc”

- So after that we start to use these files, starting from 15 then 20 then 25 then 30 then 35 then 40 sizes, and when they reach 40 size they said let stop at this point and put our silver cone and cement it and we finish our treatment, “this is an example, just get the idea of using the files from the smallest to the largest one by one”, “the silver cone is an old material was used as a filling material made from silver”.

- But this technique has so many problems, starting from the point of using large sized instrument “which is very stiff” which tend to change the curvature of the canal and its shape, and not ending with that if we just use smaller sized instrument we can’t provide the proper clean for the canal.

- So we need to replace this technique.

- And because of that the step back technique by Clem come out to us, and it’s the most used technique around the world, and all the techniques came after it, its just a modification of it.

- The idea of this technique depend on the use of small sized files for the preparation of the apical third of the canal “15, 20, 25 sizes”, “sometimes we use 30, and 35 in the case of having a canal with small curvature”, and after that we start to climb up the stair step by step, and with each step you come closer to the coronal third 1mm and we use a larger file “ it's become stiffer, but the canal becomes straighter as well. And it becomes less sensitive” we keep climbing up the stair step by step until reaching the 80 size file, after that we use the gates glidden in order to

25-11-2013 Endo sheet # 9 Ali I. Al-Shara

prepare the coronal third of the canal “because the coronal third is simple and it almost has no curvature”.

- And this is the step back technique.

- After this technique, they start to do some modifications and coming with new ones, like

Circumferential filing

Incremental technique

Anticurvature filing by Marwan Abou-Rass at 1980

It’s a technique, it’s just that in some cases, like the mesiobuccal canal of the mandibular molar and the middle mesiobuccal canal of the maxillary molar, they are severely curved, so at the area of curvature the dentine in not equally distributed, in the outer curve area there is a thick dentine, and the inner curve area it has a thin layer of dentine, so if we use our instrument and begin to cut evenly from all around the circumference we will end up having a very thin area in the inner curve side, and we might do perforation in the root canal system “when this perforation happen in the curvature area of the canal, we call it strep perforation”.

So Marwan came out by this method, in which we cut more dentine from the outer curve area in comparison to the inner one “we work by common sense”.

Question: How can we determine where is the place that has a little thickness of dentine?

Answer: We take care of this from the beginning “before starting the process of cleaning and shaping of the canal”, the Pre-Op-radiograph “it’s the radiograph which is taken before starting our operation” is mandatory, we do not do anything without it, and sometime we take another radiograph from a different angle, to have a full idea about the severity of the curvature of the canal and the thickness of the root.

- Also the step back technique has some disadvantage, and here is the explanation:

1) The studies have shown that the coronal portion of the canal contains most of the microorganisms not the apical or the middle portion of the canal, so while we are doing our apical-coronal approach, we are bushing the microorganism downward.

25-11-2013 Endo sheet # 9 Ali I. Al-Shara

2) When we insert the file and take the working length radiograph, this process will result in straighten the canal a little bit compared to the beginning, so the length is a little bit shorter, so if we take this length and work on it, actually working on a shorter canal, so we will end up with over instrumentation “the canal is dynamic, with each time we use the instrument it will change a little bit”.

- So they came out with a new technique, which is the Step Down technique “the coronal-apical approach”, so they work on avoiding the disadvantage of the step back technique in this technique, and here are the explanations:

1) For avoiding the process of pushing the microorganisms downward, we can remove it in the beginning “coronal preparation”, and then we continue as usual.

2) To avoid the error in the process of measuring the working length, when we do our coronal preparation at the beginning, we are reducing the resistance of entering the canal, and this process becomes easier and give a more accurate measurement.

- The difference between the step back technique and the step down technique is just in the arrangement of the steps,

The step back technique: working length determination, then apical preparation, then middle portion preparation, then coronal preparation.

The step down technique: coronal preparation, then working length determination, then apical preparation, then middle portion preparation, and we can do the coronal preparation again.

- In this picture we can see the pulp tissue on the barbed broach, the process of removing it is called Pulp Extirpation.

- The access cavity should be flooded with Sodium hypochlorite, in order to do the proper cleaningofr the canal.

- We make advantage of smaller sized file “flexible” in preparing the apical part of the canal, and then we start to go up step by step, by using larger size and stiffer file to create the taper, wider, cleaner canal,

25-11-2013 Endo sheet # 9 Ali I. Al-Shara

In reality it won’t be like this, it will be more like a cone shape, because the file does some smoothening for the wall of the canal.

- During the step back technique, we should do two important things:

1) Irrigation:

- We said that the canal should always be flooded with sodium hypochlorite, in order to do flushing out of all dentinal debris while we are working, and to prevent the condensing it in the apical third, and to maintain the working length.

2) Recapitulation:

- It means that while we are going back step by step toward the coronal third, we don’t forget to go and with the master file “the file that reached the working length” to the apical third between each two steps, I order to maintain the potency of the canal, and maintain our working length.

- Apical Potency: maintaining the shape of the apical foramen and not to make any deformation or dislocation for it.

In order to maintain the apical area not closed with debris, we go back with a very small file “8, 10 size” to it, and we make a small curve at the end of the file, and we insert it 0.5-1 mm beyond the working length, in order to disintegrate any debris was condensed there and to flush it out with sodium hypochlorite.

Question: How can we tell that our shaping in enough?

Answer: The entrances of the filling material will determine this thing “the technique which we will use in filling the canal”.

The filling techniques divide into:

1) Lateral condensation technique:

- We use a spreader to condense the filling material inside the canal and for this technique the spreader should enter inside the canal almost 1mm shorter than the working length beside the master cone.

- The tapering of the canal should be adequate enough to insert the spreader and accessory cone.

25-11-2013 Endo sheet # 9 Ali I. Al-Shara

2) Hot vertical condensation technique:

- For this technique the taper should be adequate to allow us to insert the blogger 4mm shorter than the working length, then we make bask fill with Obtura injection gutta percha.

This is the end of this lecture.

If you have any question regarding this sheet, you are welcomed to ask.

Good luck ^_^