A dental crown is a cap placed over a damaged tooth, restoring its shape, size, strength, and appearance. While crowns protect the tooth underneath, cavities can still develop, often hidden from plain sight. Can X-rays effectively detect these hidden cavities under a crown? This article explores the capabilities and limitations of X-rays and outlines other methods dentists use to ensure comprehensive dental health.
The Role of X-rays
X-rays provide images of teeth and their surrounding structures not visible during a standard oral examination. They work by passing radiation through tissues; denser materials absorb more radiation and appear lighter on the resulting image. Less dense areas, such as tooth decay, allow more radiation to pass through, appearing as darker or radiolucent regions.
When a cavity forms under a crown, it appears as a darker area on an X-ray, typically at the margin where the crown meets the natural tooth structure. Dentists scrutinize this border for irregularities or dark spots, which indicate demineralized tooth structure. Common X-ray types include bitewing and periapical X-rays, offering different angles and views of the tooth and its roots. Digital X-rays offer enhanced resolution and allow for contrast adjustments, making subtle changes more discernible.
Why X-rays Have Limitations
Despite their utility, X-rays have limitations when detecting cavities under crowns. The crown material itself poses a significant challenge. Metal crowns, including those with a metal base under porcelain, are highly dense and appear completely white (radiopaque) on X-rays, often obscuring the view of the underlying tooth. This “shine-through” or artifacting can hide decay, making it difficult to differentiate between healthy tooth structure and a cavity. Zirconia crowns, though ceramic, are also very radiopaque, similar to metal, further limiting visibility.
The location and size of the decay also affect visibility. Cavities on certain surfaces, like the tongue-side (lingual) or cheek-side (buccal), or those very close to the crown margin, can be hard to visualize. Superimposition, where other dental structures or the crown itself overlap the decay, can also mask its presence. Early or very small lesions may not create enough contrast to be visible on an X-ray, as significant demineralization is needed for decay to appear as a dark spot. An improperly angled X-ray may not capture the precise interface between the crown and the tooth, leading to missed decay.
Other Ways Dentists Find Cavities
Given X-ray limitations, dentists employ other diagnostic methods to detect cavities under crowns. A thorough clinical examination involves visual inspection for signs like discoloration, changes in the crown margin, or visible grey or brown spots around the crown. Dentists also use tactile examination with an explorer, checking for softness or stickiness at the crown’s edge, which can indicate decay.
Transillumination is a technique where a bright light is shone through the tooth. Decay appears as a shadow because demineralized tooth structure scatters light differently. This method can sometimes detect early decay before it is visible on X-rays. Advanced imaging technologies, such as cone beam computed tomography (CBCT), provide detailed 3D views of the tooth and surrounding bone, offering a more comprehensive assessment, especially when X-rays are inconclusive. Patient symptoms, such as pain, sensitivity to hot or cold, swelling, or a foul taste or odor, also serve as important indicators that prompt further investigation.
Addressing and Preventing Decay Under Crowns
Once a cavity under a crown is detected, treatment depends on the extent of the decay. For early-stage decay, a dental filling may suffice after removing the crown, cleaning the decayed area, and then reattaching or replacing the crown. If the decay has reached the tooth’s inner pulp, a root canal procedure might be necessary to remove the infected tissue, followed by a new crown. In severe cases where the tooth is extensively damaged, extraction may be the only option.
Prevention helps maintain the longevity of crowns and the health of the underlying tooth. Practicing good oral hygiene, including brushing teeth twice daily with fluoride toothpaste and flossing around the crown, removes plaque and bacteria. Regular dental check-ups and professional cleanings are important, allowing dentists to monitor the crown’s condition and detect issues early. Limiting sugary and acidic foods and drinks helps reduce the risk of decay formation.