Posts for tag: x-rays
The CAT scan is a relatively recent technique in dentistry, used to get an image of what’s happening deep within your jaws. You may be wondering what a CAT scan tells us that a conventional x-ray picture does not, and whether it is worth the extra expense to get one. And how does a CAT scan compare with a conventional x-ray in terms of radiation exposure?
CAT stands for “computer assisted tomography.” Often it’s just called a CT scan, for “computerized tomography.” The word “tomography” comes from roots meaning “slice” and “write.” Tomographic techniques take repeated two dimensional pictures, similar to repeatedly slicing through an object, and then assembles them with a computer to produce a three dimensional (3-D) image.
The latest type of CT scan used in dentistry is called CBCT, or Cone Beam Computed Tomography. The Cone Beam refers to a spiral beam of x-rays, which is used to create a series of two dimensional images from which a computer creates a 3-D image. Such an image is of great value in assessing problems and planning treatment.
Here are just a few examples of how a CBCT scan can be used. Orthodontists can see skeletal structures and developing teeth that are still inside the jawbone while planning strategies for directing the teeth in order to arrive at a better bite. Oral surgeons can find impacted or missing teeth, see their locations, and view their proximity to nerves and sinuses, assisting them in planning surgeries. These scans are particularly useful for root canal specialists because they show root canals that are less than a millimeter wide and even reveal accessory canals that may not be visible on conventional x-rays. In cases of sleep disorders such as sleep apnea, a CBCT during sleep can be used to view a person’s airway and how it may be blocked by the tongue and other soft tissues in a person’s throat during sleep.
Compared to background radiation, the amount of radiation delivered in dental x-rays is minimal. A CBCT delivers a dose of radiation that is less than a typical full mouth x-ray series but more than a typical two dimensional panoramic radiograph. Generally CBCT scanners deliver lower doses than medical CT scanners.
With one low-dose CBCT scan, we can get an accurate idea of the internal structure of your bones and teeth and how they are situated in relation to each other. Prior to the availability of such images, many of these relationships had to be discovered in the course of a surgery or other treatment. Thus such a scan can aid greatly in the quality of treatment you will receive.
One of the most widely used forms of dental imaging is the bitewing x-ray. So called because of the shape of the device that holds the exposable film a patient clenches between their back teeth, the bitewing x-ray is an effective means for detecting the earliest stages of tooth decay.
These early signs are small lesions on a tooth surface caused by mineral loss in the enamel. While we can identify them on front teeth through visual examination or bright lighting, they’re nearly impossible to see on the biting surfaces of back teeth. The bitewing x-ray solves this problem.
During the procedure, a narrow beam of x-rays is directed at the back teeth area. Since X-rays can transmit through solid matter, they pass through the teeth and gums to expose the film attached to the bitewing assembly.
X-rays pass through matter at different rates depending on the density of the tissue — a slower rate for harder tissues like teeth and bone and a faster rate for soft tissues like the gums. As a result, x-rays through teeth expose less of the film and appear as a lighter image than the gums. This difference is so precise even a tooth’s softer dentin appears slighter darker than its harder outer enamel.
This precision helps us identify decay lesions. Because the lesions on the enamel are less dense than the normal enamel, they’ll appear as dark spots. By detecting them at this stage we have a better chance for reversing the effects of decay or at least minimizing damage that’s already occurred.
Because x-rays emit radiation, there’s a natural concern about over-exposure and we go to great lengths to reduce it. Children may undergo a bitewing x-ray twice a year for developing teeth, while adults with healthy teeth are typically x-rayed just once a year. Advances in digital film and other technology have also helped lower the exposure rate.
Today’s standard 4-film bitewing x-ray produces about four days worth of what we receive on average from normal background radiation, so the health risk is quite negligible. The benefit, on the other hand, is much greater — the early detection of tooth decay could ultimately save a tooth.
There’s no question that x-ray imaging has transformed how we diagnose and treat dental problems. But traditional x-rays have at least one limitation — they are two-dimensional portraits that can only provide a portion of the information available. If you could view the interior of teeth or other mouth structures in three dimensions, you would have access to more detail about their conditions.
Computerized axial tomography (CAT) scanning has brought that third dimensional view to physicians generally and, in more recent years, to dentists. The latest development in this technology is known as Cone Beam Computed Tomography (CBCT). A CBCT emits a spiral of x-rays that form a cone-shaped beam that is caught on detectors. Using digital geometry, the CBCT then generates a three-dimensional image by precisely “layering” this large series of two-dimensional images caught by the detectors on top of each other.
CBCT is already making a significant impact in dentistry and its related specialties. Dentists now can visualize with amazingly precise detail the three-dimensional anatomy of the teeth, jaws, facial bone and other structures in the head and neck area. Orthodontists can examine the growth stages of a patient’s teeth eruption to better prepare treatment strategies. Oral surgeons can determine the precise location of impacted teeth and their exact proximity to nerves and sinuses. And, periodontists who specialize in gum disease and treatment can better determine the level of bone loss and gum attachment for more accurate diagnoses and effective treatment.
While a CBCT delivers a higher dose of x-rays than a traditional panoramic radiograph, it actually delivers a lower dosage than a digital standard 18 film full mouth series or than conventional medical CT scanners. The field of view also determines the level of x-ray exposure — the smaller the field of view (and more concentrated the x-rays) the higher the dosage and the better detail of anatomy.
The good news, though, is that a low dosage CBCT scan can still provide a level of detail that can provide dentists with a very accurate view of anatomical features, including bone density and mass, in three dimensions. That capability can vastly elevate the accuracy of diagnoses and lay the groundwork for effective dental treatment.
If you would like more information on the uses of CBCT scanning to help you maintain dental health, please contact us or schedule an appointment for a consultation. You can also learn more about this topic by reading the Dear Doctor magazine article “CAT Scans in Dentistry.”