A dental crown is a custom-made restoration, or cap, that covers a damaged or weakened tooth, restoring its shape, strength, and appearance. While the crown material itself cannot decay, the natural tooth structure beneath it remains susceptible to bacterial acid attack. Decay can occur under a crown, a condition dentists refer to as secondary or recurrent decay.
How Decay Forms Under a Crown
The crown’s margin, the junction where the crown meets the natural tooth structure, is the primary defense against recurrent decay. Over time, this microscopic seal can degrade, leading to marginal leakage. This process allows oral bacteria, saliva, and food particles to seep into the space between the crown and the prepared tooth structure.
Dental cement, used to bond the crown to the tooth, can slowly dissolve or wash out over years of exposure to oral fluids, widening the micro-gap at the margin. A poor fit during initial placement can also leave a gap large enough for bacteria to colonize. Once bacteria access the underlying dentin and enamel, they produce acids that demineralize the tooth structure, forming a cavity.
The tooth structure underneath the crown is often already compromised due to previous damage or large fillings, making it more vulnerable. If the original decay was not completely removed during preparation, remaining bacteria can continue to progress silently. The crown prevents the patient from effectively cleaning the area, allowing the decay to worsen undetected.
Recognizing Signs of Hidden Decay
Detecting decay under a crown is challenging because the cavity is hidden from visual inspection. A patient might first notice increased sensitivity in the crowned tooth, particularly in response to hot, cold, or sweet items. Discomfort or persistent pain, especially when biting down, suggests the decay may be progressing deeper toward the tooth’s pulp.
Dentists rely on diagnostic tools, primarily dental X-rays, for subsurface examination. A bitewing X-ray can reveal a darker area, known as radiolucency, around the crown margin or underneath the restoration, indicating a loss of tooth density.
A dentist will also perform a clinical examination, checking for physical signs such as discoloration or a dark line visible near the gum line. They may use a specialized instrument, called an explorer, to gently probe the margin for softness or gaps. A persistent bad taste or foul odor from the crowned tooth can also signal bacterial activity and chronic infection.
Treatment Options for Recurrent Decay
Once recurrent decay is confirmed, the existing crown must be removed to access the underlying tooth structure. The treatment path depends on the size and depth of the decay found after removal. For minor decay caught in its early stages, the dentist can clean out the affected area and place a simple dental filling.
After the decay is removed and the area is restored with a filling, a new, well-fitting crown must be fabricated and placed. If the decay is extensive and has reached the inner pulp chamber, a root canal procedure is required before the tooth can be restored. This involves cleaning out the infected nerve tissue and sealing the canals to prevent further infection.
In severe cases, where the decay has destroyed a significant portion of the tooth structure below the gum line, the tooth may be structurally compromised and unsalvageable. Extraction may be the only viable option to prevent the spread of infection to the jawbone and adjacent teeth. The goal of treatment is to save the tooth, but this requires sufficient healthy tooth structure to support a new restoration.