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.
It’s important for your child’s current and future health that we watch out for tooth decay. Taking x-rays is a critical part of staying one step ahead of this common disease.
But while x-ray imaging is commonplace, we can’t forget it’s still a form of radiation that could be potentially harmful, especially for a child whose tissues are rapidly developing. We must, therefore, carefully weigh the potential benefits against risk.
This concern has given birth to an important principle in the use of x-rays known as ALARA, an acronym for “As Low As Reasonably Achievable.” In basic terms, we want to use the lowest amount of x-ray energy for the shortest period of time to gain the most effectiveness in diagnosing tooth decay and other conditions.
A good example of this principle is a common type of radiograph known as a bitewing. The exposable x-ray film is attached to a plastic devise that looks like a wing; the patient bites down on it to hold it in place while the x-ray exposure takes place. Depending on the number of teeth in a child’s mouth, an appointment usually involves 2 to 4 films, and children are typically spaced at six months apart. Frequency of x-rays depends on your child’s tooth decay risk: lower risk, less need for frequent intervals.
Each bitewing exposes the child to 2 microsieverts, the standard unit for radiation measurement. This amount of radiation is relatively low: by contrast, we’re all exposed to 10 microsieverts of background radiation (natural radiation occurring in the environment) every day or 3,600 microsieverts annually. Even two appointments of four bitewings each year is a fraction of a percent of the background radiation we’re exposed to in the same year.
This conservative use of x-rays is well within safe parameters for children. As x-ray technology continues to advance (as with the development of digital imaging) we anticipate the exposure rate to diminish even more. Prudently used, x-rays remain one of our best tools for ensuring your child’s teeth are healthy and developing normally.
If you would like more information on the use of x-rays with children, 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 “X-Ray Safety for Children.”
Radiographic (x-ray) images are an indispensible diagnostic tool in dentistry. One of the most routine and useful types of x-rays dentists take is the so-called bitewing. Here are some things you may want to know about this common diagnostic procedure.
What are bitewing x-rays?
Bitewings reveal the presence and extent of decay in the back teeth, specifically in areas where adjacent teeth touch each other. Unlike other areas of the teeth, these contacting surfaces between adjacent teeth can’t be examined visually. Bitewings can also show areas of bone loss around teeth — a sign of periodontal disease; however, they are not taken for that purpose because bitewings will not show the complete root surface that is surrounded by bone.
Why are they called that?
The name “bitewing” refers to how the film — or sensor, in the case of a digital x-ray — is positioned in the mouth: The patient bites down on a little tab or wing that holds the apparatus in place.
How often do I need them?
This is determined on a case-by-case basis, with the goal of not exposing you to any more radiation than necessary — even the minimal amount found in a series of bitewing x-rays. Your individual susceptibility to caries (tooth decay) and personal dental history will play a major role in determining how frequently you need radiographic examination — and, for that matter, how often you need to come in for routine cleanings and exams.
Are they safe?
The safety of bitewing x-rays is best illustrated with a comparison to the regular daily radiation exposure we get every day from environmental sources, which is about 0.01 millisieverts — the unit of measure we use for radiation. A series of 4 bitewing x-rays exposes you to 0.004 millisieverts of radiation — less than half of the daily exposure. Undetected tooth decay, which can spread quickly through the softer inner layers of teeth, is considered much more dangerous!
If a bitewing x-ray shows that there is tooth decay, what happens next?
If the cavity is very small, we may be able to treat it during the same appointment. If not, we will make a separate appointment to make sure it is taken care of promptly. The sooner tooth decay is treated, the better!
For decades, dental x-rays have helped us accurately diagnose and treat a wide array of dental diseases and conditions. But even with recent advances in digital imaging, the traditional x-ray does have one drawback: its two-dimensional view doesn’t always provide the “big picture” that a three-dimensional viewpoint can provide.
But a new type of x-ray technology can do just that: known as cone beam computed tomography (CBCT), these machines record hundreds of digital images as a cone-shaped beam of x-ray energy is projected through a device that rotates around a person’s head. A computer then assembles the images into a single three-dimensional image that can be manipulated on screen to view from various angles. Not only does this provide greater context and detail, it does so with no more radiation exposure than a standard 20-film digital full-mouth x-ray series.
While CBCT hasn’t replaced the traditional x-ray, it’s making its mark in a number of specialized areas of dentistry. The following are just a few of the ways CBCT is improving both accuracy and treatment outcomes.
Orthodontics. CBCT can provide a much more detailed view of the entire jaw; this can help us determine the best locations for realigning teeth safely and effectively.
Dental Implants. With a CBCT scan we can precisely locate nerve canals, sinuses and adjacent teeth before implant surgery to locate the best position for the implant.
TMD Treatment. To help develop the best treatment approach for alleviating the pain and dysfunction of temporo-mandibular joint disease (TMD), a CBCT scan can provide us detailed information on how the disease is affecting a patient’s joints, teeth, sinuses and airway.
Impactions. An impacted tooth can exert damaging pressure against the roots of neighboring teeth. A CBCT scan allows us to observe the impacted tooth from various vantage points to determine the best treatment approach for neighboring teeth, nerve canals and sinuses.
If you would like more information on CBCT technology, 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 “Getting the Full Picture With Cone Beam Dental Scans.”