There are two main types of dental X-rays: intraoral (meaning the X-ray film is inside the mouth) and extraoral (meaning the X-ray film is outside the mouth).
Intraoral X-rays are the most common type of X-ray taken. You've probably had many sets of these X-rays taken in your life already. These X-rays provide a lot of detail and allow your dentist to find caries, check the health of the tooth root and bone surrounding the tooth, check the status of developing teeth, and monitor the general health of your teeth and jawbone.
Extraoral X-rays show teeth, but their main focus is the jaw and skull. These X-rays do not provide the detail found with intraoral X-rays and therefore are not used for detecting caries or for identifying problems with individual teeth. Instead, extraoral X-rays are used to look for impacted teeth, monitor growth and development of the jaws in relation to the teeth, and to identify potential problems between teeth and jaw and the temporomandibular joint (TMJ) or other bones of the face. (See the document, "Temporomandibular Disorders" for more information.)
Are there different types of intraoral X-rays that might be taken and if so, what are these types?
There are several types of intraoral X-rays, each of which shows different aspects of teeth.
Bite-wing X-rays show details of the upper and lower teeth in one area of the mouth. Each bite-wing shows a tooth from its crown to about the level of the supporting bone. Bite-wing X-rays are used to detect decay between teeth and changes in bone density caused by gum disease. They are also useful in determining the proper fit of a crown (or cast restoration) and the marginal integrity of fillings.
Periapical X-rays show the whole tooth, from the crown to beyond the end of the root to where the tooth is anchored in the jaw. Each periapical X-ray shows this full tooth dimension and includes all the teeth in one portion of either the upper or lower jaw. Periapical X-rays are used to detect any abnormalities of the root structure and surrounding bone structure.
Occlusal X-rays are larger and show full tooth development and placement. Each X-ray reveals the entire arch of teeth in either the upper or lower jaw.
What types of extraoral X-rays might be taken and for what purpose?
There are several types of extraoral X-rays that your dentist might wish to take. Among them are:
Panoramic X-rays show the entire mouth area – all the teeth in both the upper and lower jaws – on a single X-ray. Panoramic X-rays require the use of a special X-ray machine. This type of X-ray is useful for detecting the position of fully emerged as well as emerging teeth, identifying impacted teeth, and aiding in the diagnosis of tumors.
Tomograms show a particular layer or "slice" of the mouth while blurring out all other layers. This type of X-ray is useful for examining structures that are difficult to clearly see – for instance, because other structures are in very close proximity to the structure to be viewed.
Cephalometric projections show the entire side of the head. This type of X-ray is useful for examining the teeth in relation to the jaw and profile of the individual. Orthodontists use this type of X-ray to develop their treatment plans.
Sialography involves visualization of the salivary glands following the injection of a dye. The dye, called a radiopaque contrast agent, is injected into the salivary glands so that the glands can be seen on the X-ray film. (The glands are soft tissue that would not otherwise be seen with an X-ray.) Dentists might order this type of test to look for salivary gland problems, such as blockages.
Computed tomography, otherwise known as CT scanning, shows the body's interior structures as a three-dimensional image. This type of X-ray, which is performed in a hospital rather than a dentist's office, is used to identify problems in the bones of the face, such as tumors or fractures.
What other exciting developments regarding X-rays and imaging will I likely see soon in my dentist's office?
There's a newer X-ray technique that your dentist might already be using or might soon be using. It's called digital imaging. Instead of developing X-ray film in a dark room, the X-rays are sent directly to a computer and can be viewed on a screen, stored, or printed out. There are several nice benefits of using this new technology including:
The technique uses less radiation than the typical X-ray and there is no wait time for the X-rays to develop. The images are available on a screen a few seconds after being taken. The image taken, of a tooth for example, can be enhanced and enlarged many times it's actual size on the computer screen, making it easier for your dentist to show you where and what the problem is. If necessary, images can be electronically sent to another dentist or specialist – for instance, for a second opinion on a dental problem to determine if a specialist is needed. The images can also be sent to a new dentist (for example, if you move). Software added to the computer can help dentists digitally compare current to previous images in a process called subtraction radiography. Using this technique, everything that is the same between two images is "subtracted out" from the image, leaving a clear image of only the portion that is different. This helps dentists easily see the tiniest changes that might not have been noticed by the naked eye.