How to Find the MB2
Well, you guys and gals out there are at it again. You’re trying to get better. I can tell by your questions. You can always tell the conscientious dentist because they always want to know how to find that MB2.
So, the maxillary first molar is the largest tooth by volume. It’s generated more research than any other tooth in the mouth and it’s probably the most misunderstood tooth in clinical endodontics. The most common cause of failure of the maxillary first molar is failure to identify, negotiate, shape and fill the MB2 system.
So, I’ve talked about this countless times over the years and one of my little annoyances with all of you out there is you are lazy! In my world, when I have a question, I go to the web and I start Googling for information. When a lot of you have questions, you do not do this. You come to me and ask the question and make me dredge up stuff I’ve previously written about it. But, I don’t care. I’m kidding you! You cannot see the twinkle in my eye, because teachers are supposed to answer questions and that is part of the assignment.
So, I will happily answer this question, but the little comment was really, somewhat truthful in that, if you simply went to my website, there are many, many articles that I’ve written, cases that I’ve described, video clips that show how to identify and find MB2s. But, I’ll give this colleague a little glimpse because perhaps they do not like to surf the web and go to websites, and maybe they just want the answer from Cliff Ruddle’s mouth. So, from my mouth to your ears, I won’t mention your name, but here we go.
You want to know how to find MB2s.
Well, the first thing is to have anatomical familiarity. Obviously you only know what you see and you only see what you know. So if you’re thinking from micro CTs, from cleared section analysis, from lectures you’ve attended, from articles you’ve read, from chapters that you’ve seen… If you know they’re there, they’re there.
Well, John Stropko did the largest human study ever published in the world and it was in the Journal of Endodontics. I won’t be completely precise on my statistics, but what he showed is before the microscope, he was able to find, like most of us before the microscope, an incidence or frequency of MB2s in maxillary first molars about 75% of the time. When he incorporated the microscope into his clinical armamentarium, he noticed that his ability to find MB2s improved. Slowly, he saw the numbers move up to over 90%.
Now, let me get this clear for everybody. When he reported over 90% incidences of MB2 systems in maxillary first molars, it didn’t mean he got a catch or a stick with his explorer on the pulpal floor. It meant he identified it, he negotiated it with small-sized hand files, he shaped that canal, he fit a cone, and he packed it. And, when he did all those things, he counted it as an MB2. So, obviously, anatomical familiarity is important because if you don’t think they’re there, you’re not looking for them. If you know they’re there, virtually all the time, you assume it’s there until proven otherwise. Frankly speaking, I don’t know an endodontist on planet earth who’s ever done retrograde surgery and beveled back that broad MB root on that maxillary first molar and not uncovered a fin off the MB1 or an interconnector leading to a separate MB2 portal of exit.
Now, we do know that MB2s merge with MB1s and exit about 60% of the time as one foramen. But, we also know the reciprocal would be about 40% of the time, the MB2 has its own separate, distinct and unrelated portal of exit. So, they’re critically important. Not to mention, there’s anastomosing between these systems commonly. So, anatomical familiarity.
Another one is radiographs. Many dentists start procedures with a single film. This is like tying one arm behind your back and attempting to box. You’re not going to be a very good boxer. In fact, you might be 1/2 the boxer you would’ve otherwise been. Ha! Well, let’s get back to radiographs. By taking three views, three different views, you’re beginning to see more the buccolingual dimensions of any given tooth.
Another critical idea is vision. Vision can be enhanced with fiberoptic lights, with handpieces, and slowspeed handpieces that have fiberoptics inside them. Furthermore, may I mention that you can use magnifying glasses and loops, and of course, a headlamp? All this was done all through the 60s and the 70s, and into the 80s, before microscopes came in during the 80s to clinical dentistry internationally. Of course, the microscope would be the epitome of vision and vision is nothing more than magnification plus lighting.
Surgical-length burs are very useful because they remove the bulky head of the handpiece, and they get it out of the way so you have a preferable line of vision along the shaft of the bur. You can watch the bur turn. You’re not looking at the back of your handpiece. You’re looking at the bur turn.
OK. Access cavities… We could go into great detail, but always I’ve noticed in my interactions with others around the world in workshops, their greatest limitation to finding extra canals, missed canals, aberrant canals, is usually a restricted access cavity. I won’t get into this debate today, but I’m going to be doing an ongoing series of debates that are bringing up some of the great controversies hanging over clinical endodontics internationally. Certainly, one of those is access.
Let me just say this about access quickly. I have never advocated big accesses. I have never advocated gouging the internal walls, which is an indictment by some commercially-driven people. It’s nothing more than to sell their instruments. So, they have to throw surgical-length, small diameter, carbide round burs “under the bus” and they do this to promote their own burs. There’s never been a bur that I’ve ever noticed that’s perforated a tooth or gouged the internal walls. It’s always the doctor who is running the handpiece and it’s the doctor who is actually guiding that bur into the tooth.
So, I don’t want to hear any comments about “smart” burs. There are smart doctors and there are dumb doctors, but arguing with these people is like the definition of stupidity. It’s arguing with somebody who will never, ever agree with your point-of-view. They will never take the time to listen to your point-of-view. They simply will beat you down and win on experience. That’s the definition of a stupid person... They’ll beat you down and win on experience!
So, experience says that we need to have a complete access where there’s emphasis on internal flaring, flattening and finishing the axial walls. This would go a long way towards helping you find more anatomy.
Piezoelectric ultrasonics. Well, if you want to remove the bulky head of a handpiece, simply use piezoelectric ultrasonics, a generator with appropriate sized tips. It gives you unsurpassed vision down a sleek, contra-angled instrument where you can watch the tip work. I would only say, in closing about ultrasonics, it’s for doing a little job. It’s for removing small amounts of dentin in a very strategic way.
Micro-openers. They’re not talked about much, but basically it’s nothing more than a stainless steel hand file attached to an ergonomically-designed, offset handle. This gets your fingers out of the way and gets the handle on the file out of the way so you can have direct vision.
Dyes are useful. Methylene blue, Chinese red… These are ways that you can flush these reagents into a pulp chamber and then flush out the pulp chamber with water. The dye is absorbed into fissures and grooves and anomalies off of orifices that help roadmap the internal anatomy.
The “bubble test” has been mentioned. Gary Carr and I have talked about the bubble test and some of these other ideas since the late 80s because the microscope drove a lot of these ideas. The bubble test means you can flood sodium hypochlorite into a pulp chamber. Sodium hypochlorite will disassociate into sodium and chloride ions and, obviously, you can liberate free oxygen when it reacts with organic tissue. So, we look at the bubble test.
And then we can look at transillumination and, again, we’ll come back to fiberoptics. Fiberoptics can be placed above the rubber dam, below the rubber dam, and you can play light in faciolingual, buccolingual and oftentimes, even through tissue and bone, especially on maxillary teeth because the cortical plate is thinner on the buccal aspect. We can bring light in and more effectively illuminate the pulpal floor.
Explorer pressure is really something that should be emphasized. I go through explorers like most dentists go through a 10 file. The 10 file can get bent or collapsed, and we simply ask for another one. Well, I’m pushing, sometimes so firmly with a hand-held explorer that the tip, which is firm and very slender and quite durable, will collapse or bend over. But, it’s very nice to pop through a little shelf or a little roof of overlying dentin, and sometimes that’s much safer for picking up the system coronally than trying to drill or chase it.
Well, in necrotic teeth, if we use ultrasonics, the byproduct is dust and this dust can go into anatomical space, like a groove, and it will leave a characteristic “white line”. So, we can use the white line test to help us roadmap to another orifice.
There’s the “red line” test. Obviously when you open up a tooth and it bleeds, it’s bloody. So once you get the hemorrhage under control and begin to get the tissue amputated… all the level of the orifices, in furcated teeth… sometimes you might see a little bead of blood emanating out of a groove. This can be another indicator that there’s more anatomy to be found.
Taking a crown off is useful. This category could be called restorative disassembly. Simply removing a crown, especially crowns that are bulbous, can give you a much greater orientation to the prepared abutment as it relates to the underlying roots. Never hesitate taking off a crown. I know you’re trying to do the procedure through the crown and save the patient money, but if you’re going to perforate the tooth looking for a canal, it would’ve been much more cost effective to simply sacrifice the crown. And, I might add, there are some very, very nice methods that can be utilized to remove permanently-cemented dentistry. In another blog, we can perhaps go over Ruddle’s favorite removal ideas.
Perio probing is another method that’s very profoundly useful. As you run that probe around the tooth circumferentially, looking for pocket depths, you can also begin to look from the emergence pattern of how the tooth comes out of the free gingival margin. And, look at your explorer and look at the distance from the perio probe to the office itself. Remember, this has a lot to do with the next idea, which is symmetry.
In the rules of symmetry, canals should be positioned about equal distance from the canal surfaces. So, if you expose the film and you see a working length film of a file not centered in the dimensions of the root, you can pretty much be completely confident that there’s another system in that root itself.
And, we can look at the last idea and that’s color. But remember, color is an important anatomical classification because its dark and narrow lines on the pulpal floor of furcated teeth provide a visual trail of color that leads to other canal orifices.
In closing, the person that asked this question could benefit by going to my website, and for a couple of years I wrote the editorial column in Endodontic Practice called “Ruddle on the Radar”. In that ongoing, editorial column, one of the topics that I took on was “Identifying Root Canals”. What are the 14 endodontic strategies? So, they’re all listed there with a little bit more descriptive definitions than what I’ve done on this blog. But, hopefully, our time together will get you started on a whole new era of finding the MB2. Won’t that be fun?! :-)