Yes, a cavity can form under a filling, a problem known as secondary or recurrent decay. While the original filling restores the tooth’s function, the seal it creates is not permanent. Over time, the environment of the mouth and the stresses of chewing can compromise this protective barrier, allowing bacteria to re-infect the tooth structure beneath the restoration. Understanding this process helps patients recognize warning signs and take preventative steps.
How Cavities Form Under Existing Fillings
Recurrent decay develops when the integrity of the margin—the boundary between the filling material and the natural tooth structure—is compromised. This breakdown is primarily caused by material degradation, normal wear and tear, or excessive pressure from habits such as grinding or clenching. As the filling ages, it can shrink, crack, or chip, creating microscopic gaps where it meets the tooth.
These tiny spaces allow bacteria and acids to penetrate the seal in a process known as micro-leakage. Once trapped, bacteria metabolize sugars and produce organic acids. Since this area is shielded from saliva and brushing, the acid aggressively demineralizes the tooth structure underneath the filling.
Signs That Decay May Be Present
Patients often notice decay through a change in sensation or a physical alteration around the filled tooth. A common indicator is increased sensitivity to thermal changes, particularly a sharp twinge when consuming hot, cold, or sweet foods and beverages. This sensitivity occurs when the decay has progressed deep enough to irritate the underlying dentin or pulp tissue.
Pain when biting down or chewing is another frequent symptom, signaling that the decay has weakened the tooth structure or that the filling is loose. Visually, discoloration or dark staining around the edges of the filling suggests leakage and bacterial infiltration. A rough edge or a chip in the filling may also indicate that the restoration’s seal has failed.
Diagnosis and Treatment Options
Dentists use several tools to confirm the presence of recurrent decay. Dental X-rays, specifically bitewing images, are the most reliable diagnostic method because they reveal decay hidden below the filling. The dentist also conducts a visual inspection and uses an explorer instrument to check for worn spots or tiny gaps where the filling meets the tooth.
Once confirmed, treatment depends directly on the extent of the decay. For minor decay, the dentist removes the old filling, drills away the decayed tooth structure, and places a replacement filling. If the decay is extensive and has compromised a substantial amount of the tooth, a custom-fitted inlay, onlay, or a full dental crown may be needed to restore the remaining structure. If the decay has reached the pulp chamber, causing an infection or abscess, root canal therapy is required to save the tooth.
Minimizing the Risk of Recurrent Decay
Preventing recurrent decay requires consistent oral hygiene and preventative habits to maintain the filling’s seal.
- Brushing twice daily with a fluoride toothpaste and flossing every day removes plaque and bacteria around the filling margins. Flossing is particularly important as it cleans the areas between teeth that a toothbrush cannot easily reach.
- Dietary modifications, such as limiting the intake of acidic and sugary foods and drinks, reduce acid production by oral bacteria.
- Protect dental work from excessive physical stress by avoiding habits like chewing ice or biting down on hard objects. If an individual grinds or clenches their teeth, a custom-fitted nightguard can be worn to protect the fillings from micro-fractures.
- Regular dental checkups and professional cleanings, ideally every six months, allow the dentist to monitor the restorations and spot subtle signs of failure before serious decay develops.