A bitewing X-ray is a specific type of dental radiograph that provides a focused view of the crown portions of both the upper and lower back teeth (molars and premolars) in a single image. This diagnostic tool is an essential part of routine dental examinations, allowing the clinician to see areas that are impossible to view during a standard visual check. The name “bitewing” originates from the small tab the patient bites down on to hold the X-ray sensor or film precisely in place. This specific positioning provides an accurate, nearly distortion-free picture of the posterior teeth. The primary function of this image is to diagnose common dental issues early, often before they cause pain or become visible to the naked eye.
Detecting Hidden Dental Decay
The bitewing X-ray is considered the most effective method for identifying early stages of decay, particularly the kind that forms between adjacent teeth. This interproximal decay starts at the contact points where adjacent teeth touch, an area that toothbrush bristles and dental instruments cannot effectively reach or visualize. Because of this tight spacing, a dentist cannot clinically see the surface to look for changes in the enamel.
When X-rays pass through the teeth, dense structures like enamel and fillings appear white, or radiopaque. Conversely, less dense areas like decay appear darker, or radiolucent. Dental decay causes the demineralization of the tooth structure, which reduces its density and creates a dark shadow on the X-ray image. By detecting these shadows when they are still small and confined to the outer half of the enamel, the dentist may be able to recommend non-invasive treatments to stop the decay from progressing. This early detection prevents the decay from spreading into the softer dentin layer, which would necessitate a larger filling or more invasive procedure.
Evaluating Supporting Bone Levels
Beyond cavity detection, bitewing radiographs are routinely used to assess the health of the bone that supports the teeth, known as the alveolar bone. The image clearly shows the crest of the bone, which is the highest point of bone between two adjacent teeth. Dentists use this view to measure the distance from the cemento-enamel junction to the bone crest to determine if bone loss has occurred.
A healthy bone crest sits approximately 1 to 2 millimeters below the cemento-enamel junction, which is the line where the tooth’s crown meets its root. When gum disease, or periodontitis, is present, the chronic inflammation causes the gradual destruction of this supporting bone. The bitewing X-ray provides a precise measurement of this bone height loss. While bitewings are highly accurate for assessing the crestal bone, they typically only show the coronal portion of the root and may be supplemented with other X-rays if more extensive bone loss is suspected.
Checking Existing Restorations
The bitewing image allows the dentist to monitor the condition and longevity of existing dental work, such as fillings, crowns, and bridges. One of the most common issues detected is secondary decay, which is new decay that forms at the margin, or edge, of an older restoration. This occurs because bacteria can sometimes leak into small gaps between the filling material and the natural tooth structure.
The X-ray can also reveal issues with the contour and fit of the restorations. For example, the image can highlight an overhang, which is excess filling material that extends beyond the natural curve of the tooth and can create a trap for plaque and irritate the gums. By checking the marginal fit of a crown or the seal of a filling, the dentist can identify structural weaknesses that need attention before they lead to a complete failure of the dental work.