Answer to Question #14547 Submitted to "Ask the Experts"

I have been experiencing a lot of pain for the past few weeks that I believe is coming from an upper molar. Panoramic and bitewing x rays were done and I was told the tooth is fine. My pain is worsening and very much affecting my quality of life. I had this exact same thing happen on the other side and eventually a dental CT exam showed that the tooth was extremely infected. My question is would my next best step be to have another dental CT done at a separate office (Canaray), or to go back to the dentist and have a 3D x ray done? When I try to research this on the internet I am finding the terminology confusing.

I'm sorry that you are having such a difficult time right now with your tooth pain. While I can't take away your pain, I can help clear up the confusion so that you can receive the diagnosis and care that you need.

Let's start with terminology and a little bit about the imaging technique. What you mentioned in your question about "dental CT" and "3D x ray" is most usually called cone-beam computed tomography (CBCT), at least in the dental and medical world. The term "cone-beam" refers to the fact that the x-ray beam is in the shape of a cone (think, ice cream cone lying on its side) that travels around the head to provide the x-ray information that the computer uses to provide thin-layer images (tomography" means pictures of thin layers) of the structure (head, tooth, etc.). The imaging software allows the computer to rearrange the images to provide 3D information. What you called "dental CT" and "3D x ray" is exactly the same thing, just another name that your dentist may have used to try to make it simpler to understand.

What is the difference between what your dentist can provide and what Canaray can provide? Canaray is an imaging center that probably has more than one type of CBCT machine and your dentist most likely has only one (they are expensive machines). While all CBCT machines allow some variability in how much of the head to include in the scan, typically one jaw or both at a time, some of the "fancier" ones allow the user to include only a few teeth in one jaw at a high resolution (extra sharp). Based on their website information, Canaray has a machine that will do this ultra-sharp imaging, typically used for root canal diagnosis and treatment. Your dentist's x-ray machine might not be able to do this, although the images will provide a lot of information that is helpful in diagnosis.

One issue with trying to diagnose tooth pain with regular dental x rays is that the images are only two-dimensional and problems can be hidden behind other structures, particularly if the tooth has a metallic filling in it. CBCT allows the dentist to see the tooth from many different angles, making it easier to see abnormalities, such as new decay under a filling or a potential abscess. However, the imaging technique is not perfect because fillings in the tooth (or the teeth next to it), root canal fillings, nearby dental implants, or anything else metallic in the area can cause artifacts that hide things. Also, not all tooth pain has an easy-to-see cause.

You raised concern about the amount of radiation you might receive from dental CT, especially since you have had multiple medical CTs. The amount of radiation from a dental CT is generally much lower than from a medical CT, but it is highly variable, depending on the specific x-ray machine, the size of the image, and the resolution used, among other factors. The unit used to report effective radiation dose is the micro-Sievert (µSv). A typical panoramic radiograph requires about 28 µSv and a single bitewing about 20 µSv. The reported radiation dose from a CBCT that covers both jaws is 69–265 µSv and for a small image (one half of one jaw) 19–652 µSv (sometimes the small scans use an ultra-high resolution, which requires more radiation). Since your area of concern is in the upper jaw, the dentist can use a leaded shield/collar to cover the neck/thyroid region, without compromising the image.

I suggest that you discuss your tooth problem with your dentist and get his or her advice on which type of imaging would be best in your situation. I hope that you get relief soon.

Sharon L. Brooks, DDS, MS
Professor Emerita, University of Michigan School of Dentistry
Dip., American Board of Oral and Maxillofacial Radiology