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 dental X-ray taken. These X-rays provide a lot of detail and allow your dentist to find cavities, 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 cavities 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 jaws and the temporomandibular joint (TMJ, see temporomandibular disorders for more information) or other bones of the face.
Types of Intraoral X-Rays
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.
Types of Extraoral X-Rays
There are several types of extraoral X-rays that your dentist may take.
Panoramic X-rays show the entire mouth area -- all the teeth in both the upper and lower jaws -- on a single X-ray. This type of X-ray is useful for detecting the position of fully erupted as well as emerging teeth, can identify impacted teeth, and can aid 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 see clearly, 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 an individuals jaw and profile. 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 organ can be seen on the X-ray film (the organ is a 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 or Sjögren's syndrome.
Cone Beam Computed Tomography, sometimes referred to as CT scanning, shows the body's interior structures as a three-dimensional image. This type of X-ray, which may be performed in a hospital or radiology center or a dental office, is used to identify problems in the bones of the face, such as tumors or fractures. When done in the dental office with the digital CBCT machine, the amount of radiation exposure to the patient is so low that it has been measured to be in the same range as a cavity detecting bitewing xray. This is in stark comparison to hospital-based CT scans which utilize much higher doses of radiation.
CBCT scans are also used to evaluate bone for the placement of dental implants and difficult extractions. This helps the surgeon avoid possible complications during and after a surgical procedure.
Instead of developing X-ray film in a dark room, most dental offices are now using digital x-ray techniques where the x-rays are sent directly to a computer and can be viewed on screen, stored, or printed out.
There are several benefits of using this new technology:
The technique uses far less radiation than the typical X-ray and there is no wait time for the X-rays to develop -- the images are available on the screen a few seconds after being taken.
The image taken, of a tooth for example, can be enhanced and enlarged many times its 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, or to a new dentist (if you move).
Software added to the computer can help dentists digitally compare current images to previous ones 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 may not have been noticed by the naked eye.