Root Canal Therapy.
More often than not a veterinarian is going to recommend extraction of a damaged or diseased tooth. There are several instances, however, where advanced dentistry is going to be not just a pleasant alternative but a better alternative. Some teeth are strategic for the integrity of the jaw, some are strategic in use, some are both. In very specific circumstances it is preferable to leave a strategic tooth in place whenever possible. Root canal therapy (often simply called a root canal) is one method of preserving a tooth that may have otherwise required extraction. This week I will outline the steps to a root canal therapy. It is worth noting that almost more than any other aspect of veterinary medicine, advanced dentistry, root canals, restorations, crown placement and orthodontics are extremely technique sensitive procedures. Without the proper training, practice and equipment a veterinarian can't just pick up and start to perform these procedures. Even with the right equipment, training and years of practice, failures occur; and fixing a failed procedure takes a lot more skill than doing it the first time. This is one of those procedures best performed by a veterinary specialist: they can be performed by a veterinarian who has extensive training in veterinary dentistry. They should not be performed by anyone else.
The first step in a root canal is to diagnose a tooth that would benefit from the procedure. This seems straight forward enough; and in most cases, it is. Any fractured tooth with exposure of the sensitive pulp tissue requires treatment. The two treatment options are root canal therapy or extraction. Sometimes teeth will suffer a traumatic insult that does not expose the pulp but does cause it to inflame. In these teeth the pulp chamber will look markedly different from the other teeth in mouth when we take oral x rays during a dental procedure. And finally, some teeth suffer bone loss at the apex of the tooth from a multitude of causes, including but not limited to bacterial infection of the pulp.
Even after a diagnosis is made there is one more step that has to take place before we can begin. That is selecting the appropriate patient for the procedure. A root canal is not a "set it and forget it" style procedure. They require monitoring and repair if they become damaged. They also require the right type of patient/owner. If your dog broke its canine tooth chewing on rocks and you recognize that you will be unable to prevent him from continuing to chew on rocks then a root canal is probably not going to be the best treatment for your dog. In any technique sensitive practice, the key to success is knowing and avoiding situations where you are likely to fail.
Once we have diagnosed an issue that is amenable to root canal therapy and have decided that the patient is a good candidate, we can start with the physical part of the root canal. The first step is accessing the canal. This is a bit different in every animal and it is where dental x rays become invaluable. The access is different for each tooth and is different for cats and dogs. For the remainder of this we will be talking about the canine tooth in the dog. Really the only difference between teeth is the access. You want straight lines for a proper root canal and in dogs the canine tooth is very curved. Making your access as close to the gum line as possible helps considerably in giving you a single straight access shot to the apex of the tooth. The initial hole is made with a small bur on a high speed drill. It is then filed wider and sometimes a slower running drill using a special bit is used to widen the canal. Each step in a root canal can only be as good as the step before it so if the access is no good the next steps won't be much good either.
Now that we have perfect access to the canal, we have to go in and remove as much of the pulp material as possible. To do that we insert a barbed broach, a long thin file with sharp spikes that grab the pulp material and then we gently pull the material out of the canal. This step is called extirpation and with a good access hole it only takes a few minutes. Since we are talking about a dog canine tooth I will mention that you do this step twice in this tooth because you will have two access points. One point is created at the tip of the tooth and one is close to the gum line.
Now that we have removed most of the organic material from the canal, we will irrigate a little with sodium hypochlorite and sometimes a little hydrogen peroxide. This is an important step and the one most likely to cause serious harm to the patient. Sodium hypochlorite is very toxic to tissue and if any escapes into the soft tissue structures around the tooth the pain can be unbearable. During this irrigation we are also shaping our canal with a series of files designed to remove small amounts of dentin from the sides of the canal. Some people use only hand held files, some use a drill mounted filing system and some use a mixture. I use only hand held files right now but will be upgrading after a few months of training. This is my favorite step, I like to find my working length and then irrigate, then add in a little of a root canal prepping lubricant, file a little, irrigate some more and repeat. Once you are certain you have a clean well shaped canal it is time to move on to the next step.
Drying the canal involves the placement of small paper points within the canal. These absorb all of the left over irrigation fluid and prepare the canal for a sealant. I typically rinse the canal at the end of irrigation with saline then I apply my paper point. Then I remove the point and rinse again with saline and use another paper point to dry the canal a final time. In multi-rooted teeth this process becomes slightly more complicated because the coronal or top part of the canal communicates with the roots and has a transverse portion.
The dry canal is now ready to be filled. I use gutta percha: a rubbery inert substance that comes in several forms. First, a sealant is applied to get to all of the very tiny areas the gutta percha will not reach. This is done using a bit called a lentulo on a low speed hand piece to reverse drill the sealant into place. A gutta percha point is then worked into place using tools called pluggers and spreaders to do just what their names imply. Once I feel the canal is properly filled I take an x ray to be sure everything looks acceptable enough to send to another veterinarian to be critiqued. If it doesn't look good enough to show off, then I look at what needs to be done to get it there. Sometimes that means starting over, usually it just means doing a little more spreading, plugging or adding in a bit more gutta percha.
Once everything looks acceptable it is time to cover our tracks. Here we not only get a chance to do some real artwork but we get to use some pretty cool toys as well. The big risk in the failure of a root canal is that bacteria are going to get in and ruin all of our hard work. To prevent this I cover my obturation with a layer of a glass ionomer. Then I use a light cured restorative to fill the access hole and "restore" the tooth. The restorative is light responsive so we hold an intensely bright blue light to the restoration for a minute or so. Mine looks like a ray gun and makes an awesome sound while it is running.
The finished product is then x rayed one last time and the patient is recovered from anesthesia. I like to see them back in one week, repeat the x rays in one month, six months and then every year after that.
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