A dental crown is a custom-made cap placed over a damaged or weakened tooth. This prosthetic is typically composed of durable materials like porcelain, ceramic, or metal alloys. Since these materials are synthetic, the crown itself cannot develop a cavity. However, the natural tooth structure it covers remains vulnerable. Decay can still form around the edges or underneath the crown, compromising the restoration and the tooth it protects.
How Cavities Form Under a Crown
The primary site for decay is the junction where the crown meets the natural tooth structure, often called the crown margin. This area is usually located near the gum line, making it a prime location for plaque accumulation if cleaning is insufficient. When oral hygiene is inadequate, acid-producing bacteria accumulate at this interface, initiating recurrent decay, or secondary caries.
Decay begins when these bacteria metabolize sugars and produce acids that demineralize the remaining enamel and dentin of the prepared tooth. This acid exposure compromises the integrity of the dental cement that seals the crown to the tooth. When the cement washes out or the seal is broken—a phenomenon sometimes called microleakage—bacteria gain access to the underlying tooth structure.
Even a microscopic gap at the crown margin can allow bacteria to infiltrate the space beneath the restoration. Once decay begins under the crown, it can progress rapidly because the remaining tooth structure is often dentin, which is softer than enamel. Gum recession can also expose the root surface below the crown margin. This root surface is covered by cementum, which is highly susceptible to decay.
Warning Signs of Decay
Increased tooth sensitivity is a primary indication of decay under a crown. Patients often experience a sharp, lingering pain when consuming hot or cold items or sweets. This sensitivity occurs because the decay has progressed deep enough to allow temperature changes to stimulate the dental pulp, where the tooth’s nerves reside.
Another common symptom is pain or discomfort when applying pressure, such as when biting down or chewing. This pain can signal an infection that has reached the deeper tissues or a change in the crown’s fit caused by underlying structural loss. A persistent foul taste or bad breath may also indicate a problem, caused by bacteria and decaying tooth material trapped beneath the crown.
Visual signs can include a dark line or shadow appearing along the gum line where the crown meets the tooth. This discoloration may represent active decay or staining that has penetrated a compromised margin. Dentists rely on periodic X-rays to check the bone level and look for radiolucencies—dark spots—that indicate hidden decay beneath the crown.
Strategies for Crown Longevity
Meticulous oral hygiene is essential for extending the life of a dental crown and preventing recurrent decay. Brushing twice daily with a fluoride toothpaste is foundational, but special attention must be paid to the area where the crown meets the gum tissue. Flossing daily is also necessary to mechanically remove plaque from this vulnerable margin.
Using interdental cleaning aids, such as specialized floss threaders or water flossers, can effectively disrupt the bacterial film at the crown’s base. Water flossers are helpful for flushing out debris and bacteria from the tight space around the margin. Selecting a non-abrasive toothpaste can also help prevent the cement sealing the crown from wearing down prematurely.
Dietary modifications are also important, particularly limiting the consumption of highly acidic or sugary foods and drinks. These substances fuel the bacteria responsible for decay, increasing the risk around the crown margin. Furthermore, habits like grinding or clenching the teeth (bruxism) can damage the crown or weaken the cement seal. If bruxism is present, a custom-fitted nightguard can protect the crown.
Regular dental checkups and professional cleanings, typically every six months, are essential for monitoring the crown’s integrity. During these appointments, the dentist assesses the surrounding gum health and checks the crown margins for any signs of leakage. X-rays are taken to detect decay before it causes significant symptoms.