by Dennis Brave, DDS
Kenneth Koch, DMD
Regular readers of our column know how much emphasis we place on diagnosis. We also have tried to make you aware of the dramatic variation in root canal anatomy among different ethnic groups. One of the most challenging among these variations is the C-shaped canal.
C-shaped canals are quite common, especially in Asian patients. The tooth most commonly involved is the mandibular second molar. Third molars also occasionally present as C-shaped canals. But before we describe the "C" in more depth, here is something we can almost guarantee. The first time you treat a C-shaped canal you will be convinced that you have perforated the tooth. Why? Let's take a look.
C-shaped canals are generally seen in mandibular second molars that appear to have a single, large root. In this type of configuration, the floor of the chamber is lower than normal. The access penetration is quite deep. You will also notice - if the tooth is vital - a large amount of bleeding. Wise dentists know to stop and take an X-ray when things are not going as expected. Place a file in the MB canal and then take an X-ray. The X-ray will show the file in the MB canal traversing obliquely across the tooth. It looks overwhelmingly like a perforation. It is not, and you can complete the case fairly easily - if you understand the anatomy.
C-shaped canals normally have three canals. The MB and distal canals are interconnected. This connection - or "fin"- holds tremendous amounts of tissue. The ML canal usually is separate. Therefore, we refer to this shape as a C-shaped canal. Sometimes, all three canals are connected in a "horseshoe" type ring. This is called a true C-shaped canal. A true C is less common than the regular C and often is seen in third molars.
You should instrument all canals individually. However, removing all the tissue from the fins is problematic. A good tip is to keep your chamber full of irrigation agent (bleach) and then place an ultrasonic tip into it. A troughing tip (such as a CT-4) or a spreader tip will do nicely. Two things will happen: cavitation and acoustic streaming. The result of this action will be a cleansing of the webs and fins between the canals. Another tip when working on a "C" is to use a small, gates-glidden bur to open up the channel that connects the MB with the distal. Be judicious; don't overdo it. However, slightly opening this channel will allow your irrigation to work more effectively in the fins.
In terms of obturation, C-shaped canals are fun to fill. Generally, the canals will end short of the apex by 2-3 mm and then branch out. If you have properly cleaned the root canal system, your obturation will fill not only the canals, but also the fins and branches. These teeth look very cool on X-rays. This is what gets endodontists excited!
Certainly, we feel the best way to fill C-shaped canals is with a thermoplastic technique. We like to fit main cones in each of the canals and then "burn and pack" halfway down the canals with a Touch 'n Heat. We then backfill the canals and fins with the Obtura gun. This technique not only gives apical control, but the backfill of heated gutta percha from the Obtura gun allows us to fill all of the webs and fins. Certainly, there are other obturation techniques. The continuous wave technique with the System B will work well, as will Thermafil. Be on the lookout for C-shaped canals and know how to treat them. You will be very pleased with the results.
Real World Endo tip
Sometimes you will find lower second molars that have only two canals. A good tip to remember when dealing with this type of configuration is that the mesial canal, in a two-canal molar, will be considerably larger than normal and will be easy to instrument. Secondly, you will notice the mesial canal is in the center of the root and is directly across from the distal canal. Follow the dentinal map to confirm, and, as usual, take an angled X-ray.
Dr. Dennis Brave is a diplomate of the American Board of Endodontics and was the senior managing partner of a group specialty practice for 27 years.
Dr. Kenneth Koch is the founder and past director of the new program in postdoctoral endodontics at the Harvard School of Dental Medicine. Drs. Koch and Brave together are Real World Endo, an endodontic education company. They can be reached at (866) RWE-ENDO, or visit their Web site at RealWorldEndo.com.