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Marino Sutedjo

MB2 in Maxillary Molars - does it really exist?

19574 Views - Jun 2017

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The main objective of root canal treatment is thorough shaping and cleaning of all pulp spaces and their complete filling with an inert filling material. A major cause for post-RCT disease is the inability to locate, debride or fill properly all canals of the root canal system. Therefore a better knowledge of the root canal system and its frequent variations is necessary for a successful root canal treatment.

The maxillary first molar is known to be tooth that has been researched more than any other tooth in the mouth and it is generally accepted that maxillary first molars have 3 roots and 3 canals (MB, DB, P). But most studies reported incidences of a second canal (MB2) in the mesiobuccal (MB) root in over 50% of the cases and this raise a question whether this MB2 canal is really exists.

We should also be aware that the most common cause of endodontic failure of the maxillary first molar is missing this MB2 canal. Therefore, in this article I will discuss about how to find MB2 canal in maxillary first molar so that we can have an answer whether maxillary first molar have 3 roots and 4 canals (MB1, MB2, DB, P) or just 3 canals.

First, there are few factors that we have to put attention on how to find MB2 and these are:

1. Anatomy

The most important thing to know in finding mb2 is having anatomical understanding, since it’s obvious that we only know what we see and we only see what we know. So if we are thinking from cleared tooth analysis, from CBCT, from lectures we have attended, from articles we have read, if we know the MB2 are there, they are there.

John Stropko published a study in Journal of Endodontics in 1999 where he did the study of 1732 conventionally treated maxillary molars. It was reported that 73,2% MB2 was found in first molars, 50,7% in second molars and 20% in third molars. From those, it appeared that MB2 has own a separate canal in 54,9% of first molars and 45,6% of second molars and joined in all third molars. But amazingly these numbers improves up to 93% in first molars and 60,4% in second molars as the operator became more experienced, used the correct clinical armamentarium and employed magnification.

The important thing in Stropko’s study that over 90% incidences of MB2 systems in maxillary first molars is identified not just by looking and finding it with explorer. He searched for it to identified the canal. This is very important since, if we don’t think the mb2 is there, we will not be looking for it. But if we know the canal was there all the time, we will assume it’s there until proven otherwise.

2. Magnification

Magnification means enhanced vision. As I stated previously, we only know what we see, hence magnification in finding mb2 is crucial. Buhrley et al in 2002 published a study in the Journal of Endodontics about effect of magnification on finding mb2 in maxillary molars. He stated that, without magnification, participants could find the MB2 in 17,2% of the cases, while, with dental loupes, this percentage significantly increased up to 62,5%, while dental operating microscope can produce 71,1% of cases. This number means magnification in finding MB2 is a must and dental operating microscope is the best tool to use for magnification. Good lighting is also necessary to help our vision.

3. Radiograph

Radiographs are very important to help us in finding MB2. Many dentists start the procedure by taking a single film. This, too often, is not enough. By taking three different angles (SLOB), we can better see the dimensions of the tooth.

Img. 1 - We can see in image A, everything looks normal, but when we take different angled radiographs (B) we can see imediately that there is a missed MB2 (C).

Img. 2 -


4. Access Cavity

Well, access cavity as a first step in all endodontic procedure is always crucial. I have seen many clinical cases of missed canals and failing to identify extra canals in which the main cause is having an under prepared access cavity. I am not going to discuss the details of access cavity in this article, but having a complete access emphasizing on internal flaring, flattening and finishing the axial walls is necessary to help us to better inspect the anatomy. I am not saying that we must have big access, but an adequate access still can be achieved without sacrificing unnecessary tooth structure.

Removing all previous restorations such as crowns is sometimes necessary to achieve good access. This can give us better orientation to the tooth and can save us from perforation while looking for a canal.



Well, after now we know the important factors in finding MB2 let’s talk about strategy and technique. As we know, not all of MB2 can be identified easily. They will not just stay there and we just stick our files and find it. Mostly, we have to work hard to search for it, explore it, enlarge it to identify it. In this article I will also discuss about some tips and trick that can be used to help us finding MB2.


In necrotic teeth, when we create our access using either a bur or ultrasonic technology, it will produce a product which is dust that can go into anatomical spaces such as grooves. This will create an image of a “white line”. We should get suspicious of this kind of line as it can be used to help us find another orifice.

Img. 3 -


As well as in necrotic teeth, in vital teeth we have “red line” test. For sure in vital teeth after we create our access cavity and penetrate the pulp chamber, it will bleed. Once after we get control of the hemorrhage and begin to extirpate the tissue, sometimes we might see a little bead of blood emanating out of a groove. This can be another indicator that there are more canals to be found.

Img. 4 - Red test, image courtesy of Dr. Calogero Bugea

Img. 5 - image courtesy of Dr. Calogero Bugea


Bubble test has been mentioned many times since the era of microscope driven endodontic. In this test we can use a sodium hypochlorite solution into the pulp chamber and this will disassociate into sodium and chloride ions that will release free oxygen when it contacts with organic tissue. This will appear as a bubble on the chamber floor and we will able to see it through the microscope and this is another clue to help us investigate the anatomy.

Img. 6 -


Color test is also important to remember. One of the three laws of pulp chamber anatomy that were published in Journal of endodontic by Krasner et al. 2004 is the law of color change. The developmental root fusion lines or root map are narrow lines on the pulpal floor of furcated teeth and provide a visual trail that has a darker color than the chamber floor. This will lead us to other canal orifices.

Img. 7 - We can see that the floor of the pulp chamber is always a darker color than the surrounding dentinal walls and the developmental root fusion lines (root map) are darker than the floor color.

Img. 8 -


Dyes are useful. Methylene blue in this case can be used. Drop a few drops of dyes into the pulp chamber and then rinse the pulp chamber with water. The dye will go into fissures and grooves that help us to roadmap the internal anatomy.


After completion of the access cavity, we can use several tests above to help us find the location of MB2 canal. In some cases, with the help of magnification, the MB2 canal orifice can be located directly after we do some of the tests. But for sure this will not occur in all cases. There are also two important stages to find MB2 canals. The first one is to find all the main canals of the first maxillary molar. In this case it will be Mesiobuccal canal (MB1), Distobuccal canal (DB) and Palatal canal (P). For these three canal orifices, we have to remember the anatomical key for easier identification.

- Mesiobuccal (MB1): Located slightly distal to MB cusp tip

- Distobuccal (DB): Located distal and slightly palatal to MB1 canal. It tends to be in line with buccal grove

- Palatal (P): Located distal to Mesio Palatal (MP) cusp tip

The second stage now is to identify the location of the MB2 canal orifice. The MB2 canal usually located palatal to MB1 canal and slightly mesial to a line drawn between MB1 and Palatal canal

Img. 9

Img. 10 - I

n most teeth, even after the MB2 canal orifice is located, we still cannot negotiate the canal easily, unless some dentin was removed from the orifice level apically. For this purpose we can use long shank, low speed burs such as Munce discovery burs. These burs are very useful because they remove the bulky head of the handpiece, and they get it out of the way so we have a preferable line of vision along the shaft of the bur. We can watch the bur turn and we are not looking at the back of our handpiece instead we are looking at the bur turn.

Ultrasonic tips also can be used very well if we want to have a good vision without any obstacles from the bulky head of a handpiece. Simply use piezoelectric ultrasonics with appropriate tips such as Start-X # 3 and it will give us better vision through a sleek, contra-angled instrument where we can watch the tip work.

A rotary instrument that has a very good cutting ability is also one of my favorites to search for an opening for root canal negotiation. Use the rotary instruments such as ProTaper SX, WaveOne Gold or Reciproc blue in a brushing motion away from the furcation to remove the triangular dentin at the orifice level and reduce the coronal interference.

The Endo explorer is not talked about much in exploring the MB2 canal orifice, but basically this explorer is quite important. Since it’s very nice to dig out little roof of overlying dentin, and sometimes this is much safer than trying to use a bur to drill it. When using the explorer, it’s advisable to push firmly the overlying dentin with the tip. The tip of endo explorer itself is pretty durable.

After removing some dentin, for sure we hope to see a small opening to the MB2 canal and we are ready to explore and negotiate those canals. In negotiation there are no differences from any other root canal negotiation. Use a mechanical glide path instrument, small hand file or a micro opener.

For micro openers, basically it’s just a stainless steel file that's attached to a handle. This ergonomic handle will get your fingers out of sight and the file's handle away so we can have direct vision.

Img. 11 - Sometimes with K-file our vision gets blocked by the handle of the file

Img. 12 - Our finger can also block our sight when we do our root canal negotiation

Img. 13 - Using micro openers can enhance our vision


Mesiobuccal roots of maxillary first molar teeth had more variation in their canal system than the distobuccal or palatal roots. Many studies reported a high incidence of MB2 root canals in maxillary molars. A good triangular access cavity, careful examination of the pulpal floor is important to enhance detection and mapping of the mesiobuccal root canal system with the potential to identified the MB2 canal and improve the quality of root canal treatment.


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