You are probably already familiar with the traditional dental X-rays routinely performed at check-ups. Sometimes these do not produce an image that is detailed enough for us to accurately diagnose a condition or plan a treatment. In situations like these, we have the choice between an MRI face scan or a cone beam CT scan.
An MRI face scan and a CBCT scan both have the capability to produce more detailed images of the mouth than traditional X-rays. Each has its own advantages and disadvantages. We believe that the risk of adverse events from an MRI face is greater than that from a cone beam CT scan. Therefore, absent any contraindications, we prefer to perform a CBCT, which we can do in our office.
How Are Cone Beam CT Scan and Facial MRI Different?
Computed tomography is a type of X-ray exam in which a series of two-dimensional images of a part of the body is taken in quick succession. Using a computer, the pictures are then collected and combined to produce a single three-dimensional image that is much more detailed than anything a traditional X-ray could produce.
First coming into widespread use approximately 20 years ago, a cone beam CT is used specifically in dentistry and oral surgery. It uses a cone-shaped X-ray beam to focus directly on the mouth. It produces images of similar quality to a regular CT scan but uses a much more compact machine and exposes the patient to much less radiation.
MRI also produces detailed images of internal body structures but without X-rays. Instead, an MRI uses radiofrequency energy, i.e., radio waves, and strong magnetic fields to produce images.
Because most of the signals picked up by the MRI face scan are produced by protons in the body’s water and fat molecules, it is most effective at imaging soft tissues, such as muscles, tendons, or ligaments. Because a cone beam CT uses X-rays, it is more effective at imaging bones, teeth, and other hard tissues. During a 2016 study, an analysis of 2D and 3D images produced by both MRI and CBCT showed them to be almost equally accurate despite the different methodologies.
What Are the Potential Risks of MRI?
MRI does not expose the patient to radiation as a CT does and is generally considered to be very safe. However, it does pose other potential health risks.
Older MRI machines produce loud banging noises that could damage a patient’s hearing. While some of these older machines may be still in use, newer devices have eliminated the dangerously loud noises.
Newer MRI designs have also made the tunnels shallower and wider. Nevertheless, patients with claustrophobia still may have trouble tolerating the procedure. There are open MRI units available to accommodate them, but these do not always produce reliable images.
Exposure to radiofrequency energy and/or magnetic fields can cause the body to heat up. The longer the MRI scan lasts, the greater the potential for overheating. The length of the scan depends on the size of the area being assessed, with larger areas taking more time. An MRI generally takes between 15 and 90 minutes to complete.
It is not only the body itself that may become heated during an MRI face scan but any metal in the body or adjacent to it:
- Implants, such as cochlear implants, intracranial aneurysm clips, or surgical hardware
- Foreign bodies, such as shrapnel or bullets
- Jewelry that cannot be removed from body piercings
Metal is sometimes also found in unexpected places. Socks, underwear, and other types of street clothes sometimes contain traces so small as to be undetectable. Nevertheless, an MRI can cause heating of these trace metals if the clothing is worn during the scan. Heating of metal from MRI has been known to result in second-degree burns.
A study conducted in Turkey in 2018 showed an increase in mercury vapor from silver amalgam fillings tested in artificial saliva in test tubes outside the body when exposed to certain high-strength MRI scanners. More research is needed to determine whether fillings inside the mouth would release vapor in amounts that would be harmful to the body.
Ordinarily, MRI has no measurable effect on a patient’s fillings, so long as they are in proper condition. However, the fillings may affect the MRI, causing distortion of the image. The same is true of orthodontic braces.
The magnetic field generated by the MRI machine is extremely powerful. Metal objects both large and small can be drawn forcefully into the machine if within the MRI environment. Despite safety protocols in place to prevent objects such as these from entering the environment, sometimes an oversight takes place. A patient can suffer injury that may be serious due to the trauma that results from being struck with such a projectile.
What Are the Potential Advantages of Cone Beam CT Scan?
In patients without metal in their bodies, the risks associated with MRI are relatively small. Nevertheless, CBCT scan may offer other advantages apart from safety concerns.
An MRI can take a long time to perform, sometimes over an hour. A CBCT is completed in less than a minute. It can be performed right in our office, while we would have to refer you to another location if we were to order an MRI for you. You would have to schedule a separate appointment and travel to the MRI location.
A cone beam CT machine is much smaller than an MRI device or a regular CT machine. Rather than sending you into a tunnel, the CBCT device circles around you. While we may sometimes ask you to lie down on an exam table, often you can sit up while the scan takes place. In either case, you remain out in the open, which makes it more comfortable for patients with claustrophobia.