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 on 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 temporo-mandibular joint or other bones of the face.
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 soundness (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.
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 emerged as well as emerging teeth, can identify impacted teeth, and aid in the diagnosis of tumours.
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 otherwise difficult to see clearly – for instance, because other structures are very close 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.