An old filling has become sensitive: does it need to be replaced, can it be repaired, and what should I ask?

Why a filling that was fine for years can start to bother you

A filling has no nerve of its own, so when the tooth around it becomes sensitive, the sensation is coming from the tooth. Enamel has no nerve supply. Dentin, the layer underneath, is porous and connected to the pulp, so anything that exposes dentin or lets fluid, sugar or temperature reach it can produce a brief, sharp response. Around an aging filling, the usual ways that happens are:

• A gap at the edge. Fillings can wear, chip or crack over time, and the seal between the filling and the tooth can open. A gap lets cold and sweet reach dentin and gives plaque a place to collect.
• Decay beside or under the filling. Teeth that already have fillings are at higher risk of new decay at the edges of those fillings, and decay under a filling is often silent until it reaches dentin.
• A crack in the tooth. A tooth that has been filled has less of its own structure left, and cracks can start at a corner of the filling. Cracked teeth classically hurt on biting or on releasing the bite and react to temperature, and the crack itself may not show on an X-ray.
• Wear or recession next to the filling. If the gum has pulled back, the root surface beside the filling is exposed. Roots are covered by cementum, which is softer than enamel, so they are sensitive and decay more easily.
• The nerve itself. Occasionally the pulp is inflamed, from deep decay, a crack or an old injury. Pain that lingers after cold or that starts on its own points toward the nerve rather than the filling edge.

The examination, not the sensation alone, tells these apart.

What changes the answer

The trigger and how long it lasts

A short twinge with cold or sweet that stops within seconds usually means exposed dentin: a gap, a worn margin, a bare root or early decay. Pain that lingers well after the trigger is gone, or that comes without a trigger, usually means the pulp is involved. The second pattern is the more urgent one.

Pain on biting

Pain when you bite, especially a sharp pain when you let go, is the typical sign of a cracked tooth. Your dentist may have you bite on a small instrument tooth by tooth to find the cusp (one of the raised points of a back tooth) involved. If a crack is found, the decision is no longer only about the filling; it is about holding the tooth together.

What the filling is made of, and how big it is

Tooth-colored composite, silver-colored amalgam and other materials wear and fail in different ways. A large filling leaves thin walls of tooth around it, which is why a bigger filling is more likely to be part of a crack or to need a restoration that covers the cusps. Our guide on tooth-colored filling materials explains what each material is suited to.

Whether the filling is amalgam

Sensitivity next to a sound amalgam filling is not, by itself, a reason to remove it. The FDA does not recommend removing or replacing amalgam fillings that are in good condition unless it is medically necessary, because removal takes away healthy tooth structure and briefly raises mercury vapor exposure. If the amalgam has cracked or there is decay beneath it, replacement may be the right call; our guides on a cracked amalgam or decay underneath and on the FDA's guidance for sound silver fillings go through the difference.

Your decay risk

Past decay and existing fillings are themselves indicators of higher risk of new decay. With dry mouth, frequent sugar or trouble cleaning between teeth as well, your dentist may lean toward treating a doubtful edge rather than watching it, and will likely discuss prevention alongside the repair.

How much tooth remains

The more natural tooth that is left, the more options exist. A tooth with a small filling and a chipped edge can often be repaired conservatively. A tooth that is mostly filling, with a crack and a cusp that flexes, may need partial or full coverage so the remaining walls are protected, which is the approach described on our biomimetic dentistry service page.

Patterns and how urgent they usually are

The table shows what each pattern most often means and how quickly to be seen. It is a guide, not a diagnosis; one symptom can have more than one cause.

Sweet sensitivity in a single tooth has its own guide: sweet foods hurt one tooth.

Repair, reseal or replace: what each one does

Repair or reseal. When the filling is sound but a small corner has chipped or a margin has opened, the dentist may in selected cases be able to repair only the defective area, bonding new material into it or resealing the edge, rather than removing the whole filling. This keeps the rest of the filling and nearly all of the tooth around it. It cannot fix decay that has spread under the filling, and it cannot address a crack running through the tooth.

Replace. When the margin is leaking widely, there is decay beneath or beside the filling, or the filling has fractured, the old material usually comes out so the decay can be removed and the cavity restored fresh. Replacement usually removes some additional tooth each time it is done, which is why it is chosen when repair would leave disease behind rather than as a default.

A larger restoration. If removing the old filling and decay leaves thin or cracked walls, a filling may not be enough to protect the tooth. An onlay (a bonded restoration that covers part of the chewing surface) or a crown that covers the weakened cusps may be discussed. Whether that is needed is decided after the old filling is out, so ask beforehand what the possibilities are and how you will be told if the plan changes.

Treating the nerve. If testing shows the pulp is inflamed or infected, the nerve is addressed before the final restoration is decided.

Which path applies is decided by the exam: probing the edges of the filling, looking for stain or softness, bite and cold testing, checking the gum level and taking X-rays to see what is under and between the teeth. X-rays are chosen based on your history and findings rather than on a fixed schedule. No one can promise beforehand that a repair will avoid a crown, because the condition of the tooth under the old filling is not fully visible until it is opened.

Questions to ask at the appointment

• What does the X-ray show under and beside the filling? Ask to see it, and ask whether anything is uncertain.
• Is the filling itself sound, or is it the tooth around it? This frames whether repair is even on the table.
• Can the edge be repaired or resealed instead of the whole filling coming out? If not, ask what specifically rules it out.
• What would waiting change? Some findings can be watched; a leaking margin over decay usually grows. Our guide on delaying a recommended filling covers how fast that tends to happen.
• If the decay is deeper than expected, what are the options, and will you stop and tell me? Agree in advance how a change of plan is communicated.
• If the filling is amalgam, is there a reason to remove it, or is it still sound?
• How will the bite be checked afterward, and what should I feel in the first weeks? Some sensitivity after a new filling is common; pain on biting that persists deserves a follow-up visit.
• What would lower my risk of this happening to other fillings? This is where fluoride, diet and cleaning between teeth come in.

When to seek emergency care instead

Difficulty breathing or swallowing, facial or neck swelling that is spreading quickly, fever together with facial swelling, uncontrolled bleeding or a severe injury to the face or jaw are medical emergencies. Call 911 or go to the nearest emergency department first, not to a dental request form. A dental appointment to address the tooth comes afterward.

The next step

If a filling has begun to react to cold, sweet or biting, note which trigger sets it off, how long it lasts and which tooth it seems to be, and share that when you request a visit. Bring any previous X-rays so the edges of the filling can be compared over time. You can request an appointment online or call the office during its hours; a request is not a confirmed appointment, and the team will follow up to schedule.