“I Had A Root Canal, But My Tooth Still Hurts!”

Author: Dr. Sarah Mischo, DMD

Root canal therapy is performed for many reasons, and more than 15 million people undergo root canal therapy every year. So, you are not alone if you have ever needed one! Patients requiring a root canal may have a cavity that has grown so large that it has now come in close proximity with the nerve (also called the pulp) of the tooth, or they may have experienced trauma to the tooth which has resulted in the nerve beginning to die. One tool dentists use when deciding if a patient could benefit from root canal therapy is radiography, or x-rays. On a radiograph, a tooth with a dark circle around the apex (or end of the root) is one that will likely require a root canal. This halo is called a periapical radiolucency, or PARL, and it is usually formed by the body’s response to an infection in the tooth that has reached all the way into the nerve. The inflammation caused by the infection will start to build within the enclosed pulpal space and will eventually burst out of the end of the root into the surrounding bone. The secondary effects from the infection ultimately lead to soft tissue and bone destruction in the area which appears as a dark spot on the radiograph as well as other clinical signs. 


(In the photo, the yellow outlined lesion is the PARL, the photo on the right is the tooth after root canal therapy.)

After treatment with root canal therapy, tooth pain will go away completely for most patients, and after several months, the bone around the affected tooth will heal, resulting in disappearance of the PARL on x-ray. According to a recent article published in British Dental Journal, in about 5-15% of cases pain may persist or the x-ray changes seen before the root canal may not improve even if the dentist performs the first root canal perfectly. This can happen for a number of reasons, including continued infection of the tooth’s root, infection of the area around the tooth, scar tissue around the apex of the root, or a number of other inflammatory factors. In these cases, your dentist may recommend monitoring the lesion if you are not having any symptoms, re-treating the tooth with another root canal, or they may refer you to a specialist for other procedures designed to help clear any infected or inflamed tissue.

If your dentist is considering root canal therapy as part of your treatment plan, feel free to ask what they are seeing on exam and radiographs that caused them to recommend that treatment, and if they mention you happen to have a PARL, take a look at the x-ray and see if you can point it out!