Superb endodontist (and awesome human being) Neha Shah DMD writes our latest guest post and explains a pervasive mystery in dental treatment:
Many people are surprised when they hear that they need a root canal on a tooth that has already been previously root canal treated. Wasn't the entire purpose of doing the root canal to not to ever feel pain again in the tooth? Commonly I hear from patients, “All the nerves are out, so how come this tooth is hurting?” The most common misconception from patients is that when a tooth has had root canal treatment, it is as if the procedure has created a force around it so strong that not even kryptonite can penetrate it. However, this is far from reality.
When a tooth has been treated for a root canal, it is in essence "rendered dead." A tooth that has had root canal therapy is essentially devoid of the living pulp tissue at the core of the tooth and therefore not able to respond to temperature stimulation. So the tooth is not able to tell you if something is hot or cold. However, it is still able to perform other functions of a mature, vital tooth because it still has the basic structures of a natural tooth namely enamel, dentin and cementum. This is what renders it susceptible to all of the threats that a vital healthy tooth is susceptible to. In fact, some may argue that a root canal treated tooth is slightly more vulnerable than a healthy, vital tooth. This means a tooth that has been treated for a root canal is susceptible to decay (cavity), fracture, and infection just like any other tooth in the mouth. So it is imperative that a root canal treated tooth is properly cared for and protected.
One of the biggest threats to our teeth is BACTERIA. Our teeth are constantly bathed in saliva that contains bacteria. These bacteria which are naturally present in our mouth are opportunists and when the environment is ripe will attack the basic structures of the tooth. So at every opportunity, at every level from performing the root canal, to sealing the root canal, to sealing the tooth, this basic goal of keeping the bacteria out is rigorously practiced by the dental health provider and encouraged to the patient.
So what is causing that previously root canal treated tooth to hurt? Infection and Inflammation. For every infection there is associated symptomatic (painful) or asymptomatic (no pain) inflammation. The primary reason why root canal needs to be redone is for what we term "coronal leakage" ("coronal" meaning "crown"). What this essentially means is that bacteria have penetrated through and into a previously disinfected root canal system. Other less common factors that lead to retreatment is a previously untreated canal, undetected root fracture, or persistent infections within the root canal system due to complex anatomy or extraradicular infections. Regardless, the common thread that runs through these causes of failures is again bacteria, "bugs," or microorganisms.
In a nutshell, the cause is bacteria and the treatment is disinfection. Disinfection is precisely the primary goal of retreatment therapy. During retreatment any existing restorations or posts leading to the root canal system have to be disassembled. The root filling material has to be removed and the entire root canal system has to be disinfected. Once the disinfection process has been completed, which usually is completed in two or more visits, new root filling material is then placed and once again an opportunity has been set to seal the tooth properly and restore it to full function. In essence, retreatment is like giving the tooth a second life.
In some ways you can use the analogy of the life lines from “Who Wants to be a Millionaire?” #1 life line for a tooth is root canal therapy. #2 life line is your endodontist when (s)he performs retreatment procedure due to reinfection of the initial root canal therapy. Your last life line is your endodontist when (s)he performs an apicoectomy on a tooth that has already had root canal therapy more than once. Your million dollar is when you save yourself of the aggravation of extracting the tooth and finding a way to replace it with a prosthesis.
To illustrate, here is a case that has failed for many of the reasons mentioned above:
For the above case, the tooth’s prior root canal had to be disassembled through a permanent crown. Goals of the retreatment for this case were to remove the post, remove separated files from the canals, locate additional canals, remove existing root filling and fully debride and disinfect the root canal system, and then medicate to create an environment for healing. The last two x-rays show the finished treatment.
You may realize from the similarities on the X-ray that the tooth behind the one that was treated is in a similar predicament. It too will require retreatment for long term success.
Root canal therapy is a highly predictable, highly successful procedure when the tooth is treated and restored properly. Like any medical/dental procedure, the responsibility of performing the procedure properly lies in the hands of the health care provider but the care and maintenance after the procedure is shared by the patient and the provider. Remember, if at first you don’t succeed, try, try again.