Answer to Question #13785 Submitted to "Ask the Experts"

Category: Medical and Dental Patient Issues — Dental

The following question was answered by an expert in the appropriate field:


I had a cone beam computed tomography (CBCT) scan of my tooth to assess a root canal. I've read these types of exams vary in the amount of radiation they produce, and I am worried because I don't want a large dose of radiation. What is the typical dose of this exam? Could you provide a comparison to the dose of other CT scans


Before I provide dose information, I would like to describe the root canal procedure and why more and more dentists, and particularly endodontists—root canal specialists—are using cone CBCT to aid them in treatment. Teeth consist of hard calcified layers—enamel, dentin, and cementum—surrounding the "living" portion of the tooth, the dental pulp. There is a relatively large amount of pulp tissue in the crown of the tooth (the part visible in the mouth) and then smaller linear amounts in canals down each root. Teeth in the front part of the mouth typically have one root and one root canal but teeth in the back, the molars and premolars, have multiple roots and may have multiple canals in each root.

When a tooth is injured, whether by trauma, dental decay (cavity), or even a very large deep filling, the pulp can become inflamed and cause pain, swelling, or an abscess, depending on how bad the condition is. The goal of root canal treatment (endodontic treatment) is to clean out the inflamed pulp tissue from the root canals and then seal the tooth up, letting the body then finish the healing if the inflammation or infection moved out of the tooth into the surrounding bone before treatment was started.

Successful root canal treatment means that all of the diseased pulp tissue must be removed, but this can be difficult because some of the root canals are very small and some roots have multiple canals. Standard dental radiographs (x rays) can be helpful in identifying most of the canals but having a 3D view gives the dentist a better chance of finding all of the canals and analyzing their shape (some of them have distinct curvatures) so they can be cleaned and then filled completely.

The CBCT exam used for root canal treatment is typically done with a small field of view (FOV) scanner, one that covers just the jaw of interest, not exposing tissue either above or below the specific jaw. The median effective dose for a small FOV CBCT scan is 50 µSv. The effective dose takes into account the amount of radiation exposure, the tissues exposed, and the sensitivity of those tissues to radiation and is commonly used when comparing radiation doses. Larger FOV CBCT scans have a median effective dose of 100–120 µSv. For comparison, a medical CT scan of the jaws using a multidetector computed tomography (MDCT) has a median effective dose of 650 µSv and an MDCT exam of the entire head has a median effective dose of 2,000 µSv.

The American College of Radiology has categorized radiation exposures into five levels, based on dose and risk to the patient. The small FOV CBCT scan falls into the lowest category.

If a CBCT scan is not done, the dentist typically must take multiple standard dental x rays from different angles before root canal treatment in order to try to find all the root canals that may be hidden.

The bottom line is that a small FOV CBCT scan is a low dose examination that increases the likelihood that root canal treatment will be successful. You do not need to be worried about this examination: the risk is very low and the benefits are high.

Dose information in my response is from the most commonly used radiology textbook in dentistry: Sanjay Mally and Ernest Lam's White and Pharoah’s Oral Radiology, Principles and Interpretation, 8th ed. Elsevier, St. Louis, 2019. P29.

Sharon L. Brooks, DDS, MS

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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