There are two major types of x-rays: intraoral and extraoral. Intraoral x-rays are performed with the x-ray film inside the mouth. These x-rays help reveal cavities, the state of a patient’s tooth roots, the health of the bony area that surrounds the teeth and the status of the patient’s tooth health. Types include:

• Bite wing x-rays. Highlight the crowns of the teeth and provide images from the crown to the level of the jawbone. Each x-ray shows the upper and lower jaw in the back portion of the mouth. Bite wing x-rays can also show areas between the teeth that cannot be seen directly. They can detect cavities on the surfaces of teeth that touch adjacent teeth. These x-rays may be taken from the time a child’s teeth in the back of the mouth begin to contact each other.
  
  
• Periapical x-rays. Highlight the entire tooth from the crown down past the end of the root to the portion of the jaw where the tooth is anchored. Each x-ray shows either the upper or lower jaw in one portion of the mouth and typically captures information for two to three adjacent teeth. Periapical x-rays can be used to detect infections and gum disease.
  
  
• Occlusal x-rays. Highlight tooth development and placement. Each x-ray shows the full arch of teeth in either the upper or lower jaw. The x-ray machine may be pointed down near the nose or straight up from the chin, depending on whether the upper or lower jaw is being radiographed. Occlusal x-rays of the lower jaw are useful in detecting salivary stones (calcium deposits that clog the ducts carrying saliva). Occlusal x-rays of the upper jaw may reveal impacted or extra teeth.
  
  
• Digital radiographs. A new technique in which an electronic pad or sensor is used to record the x-ray instead of film. The recorded image is sent to a computer and displayed on a monitor. The radiographs that are taken can be digitally compared to earlier radiographs (subtraction radiography), offering a precise comparison of any changes. The technique is expensive and is not available in many dental offices. However, it is likely to become the standard process for taking images of teeth in the future.   

Extraoral x-rays are made with the film outside the mouth, and provide an overview of the jaw and skull. These images are less detailed than intraoral x-rays, so they are not used to detect abnormalities in individual teeth. Instead, they are used to examine the relationship between the teeth and the jaw and to look at areas of the face (e.g., temporomandibular joint) that may be the source of dental problems. Types include:

• Panoramic radiographs. Highlight the entire mouth, including all the teeth, the temporomandibular joints and the sinuses. A special machine with a tube head circles around the patient’s head to capture these images. The patient must remain very still during the process, and is aided in this task with chin and forehead rests, side head positioners and bite-blocks. It is useful in detecting impacted teeth, jaw cysts and jaw fractures.
  
  
• Tomograms. X-rays performed to highlight one layer of anatomy while blurring out other adjacent layers. Tomograms are used to produce images of structures that are difficult to detect through standard x-rays. They are useful in detecting fractures of the facial bones.
  
  
• Cephalometric projections. Taken of the entire side of the head, they highlight the teeth in relation to the jaw from a profile view. These x-rays are often used by orthodontists to determine the best way to align teeth.
  
  
• Sialography. Highlights the salivary glands, which are not dense enough to show up on most x-rays. During a sialography, a radiopaque contrast material is injected into the salivary glands and appears on film to reveal blockages (e.g., salivary stones) and other conditions such as Sjögren’s syndrome.
  
  
• Computed tomography. Highlights the bones of the face and reveals problems such as tumors or fractures. This type of x-ray is usually performed in a hospital but some dental offices are now performing them to analyze bone structure for dental implants. A dentist may refer a patient for such a test if necessary.