Why Do I Keep Getting Infections Around Old Dental Work?

Patients describing this pattern usually tell the same story. A course of antibiotics settles it. A few months later it comes back. Another course, another few months, and the cycle repeats.

The cycle is informative. Antibiotics reduce the bacterial load enough for symptoms to subside, but they do not close the route the bacteria are using. As soon as the drug is out of the system, the source is still there and repopulates.

Recurrent infection around an existing restoration is therefore not really an infection problem. It is a structural problem that presents as infection, and the useful question is which structural problem.

Dental infections are usually associated with a physical source: a necrotic pulp, a space beneath a restoration, a crack, or a deep periodontal pocket. That source is often poorly perfused, so the antibiotic reaches it at low concentration and the bacteria within a mature biofilm are considerably less susceptible than free-floating organisms.

The result is symptom control rather than resolution. UK prescribing guidance reflects this: antibiotics are indicated where there is spreading infection or systemic involvement, as an adjunct to definitive treatment, not as an alternative to it.

Repeated courses also carry real cost — antimicrobial resistance, disruption of gut flora, and delay while the underlying problem progresses. Our articles on whether antibiotics can replace root canal treatment and whether you need antibiotics for a tooth infection cover the indications.

The junction between a filling or crown and the tooth is the vulnerable point. Over years, the restoration and the tooth flex slightly differently under load, cement can dissolve, and a microscopic gap can open.

Bacteria enter that gap, decay develops beneath the restoration where neither brush nor floss reaches, and it progresses towards the pulp — frequently without any visible change on the surface. This is why decay under an old crown is often discovered on a radiograph rather than by looking.

Our articles on cement washout in dental crowns and how crown margin placement affects gum health cover the mechanism.

A restored tooth is weaker than an intact one, particularly where the restoration is large and the remaining walls are thin. A crack running through a cusp or down towards the root creates a pathway that no restoration can seal, because it moves under load.

Cracks are notoriously difficult to see on radiographs, because a fracture line parallel to the beam does not register. The usual clue is pain on releasing a bite rather than on clenching, and infection that recurs in a tooth that otherwise looks sound. Our article on root canal treatment for cracked tooth pain covers this presentation.

A vertical root fracture is generally not restorable, and recognising it early prevents further treatment that cannot succeed.

Root canal treatment aims to remove the infected pulp tissue and seal the canal system. Where some of that system remains uncleaned, bacteria persist and infection recurs at the root tip.

Common reasons include an untreated extra canal — upper molars frequently have a fourth canal that is easy to miss, and lower incisors often have two — a canal that was blocked, curved or calcified and could not be fully instrumented, a seal that has degraded over time, or bacteria re-entering through a leaking restoration above a sound root filling.

Our article on apical periodontitis and infection spreading into the jawbone explains what happens at the root tip, and whether you can have root canal treatment through an existing crown covers access.

Not all recurrent infection is inside the tooth. A deep periodontal pocket beside a restored tooth harbours bacteria and produces localised swelling and discharge that can look very similar to a tooth-origin abscess.

Restorations that extend deep beneath the gum, or that are over-contoured, make the pocket harder to clean and perpetuate the problem. Our article on the difference between a toothache and a dental abscess covers distinguishing the sources.

Sometimes both are present — infection from inside the tooth draining through the periodontal ligament, or a deep pocket reaching the root tip. These need both problems addressed, and the sequence matters.

A contact point that is open or badly shaped allows food to wedge between teeth repeatedly. The resulting chronic irritation produces localised gum infection that recurs predictably, and it resolves when the contact is corrected rather than when antibiotics are taken.

The features worth noting, because they help your clinician:

• Symptoms returning in the same tooth or same area each time

• A gum boil or small swelling that appears, discharges, resolves and returns — this is a sinus tract, and it is a reliable sign of a chronic source

• A persistent bad taste in one area

• Symptoms that improve on antibiotics and return within weeks of finishing

• Pain on biting, particularly on release

• Sensitivity to cold that lingers rather than passing quickly

• Nothing visible despite the symptoms

Our article on symptoms of mouth infections covers the broader picture, and dental abscess symptoms the acute presentation.

Some findings need same-day attention rather than a routine appointment:

• Facial swelling, particularly if it is spreading or affecting the eye or neck

• Difficulty swallowing, breathing or opening the mouth

• Fever with a dental problem, which suggests the infection is no longer localised

• Rapidly worsening pain with general malaise

Our articles on fever with facial swelling and what constitutes a true dental emergency explain the thresholds.

Finding the source is the whole task, and it takes more than looking.

History — which tooth, how often, what triggers it, what the pain is like and how it responds to temperature and biting.

Clinical examination — checking each restoration margin, testing for tenderness to percussion and to biting on individual cusps, probing around the tooth, and looking for a sinus tract.

Sensibility testing — cold and electric pulp tests establish whether the pulp is alive, which distinguishes a tooth needing root canal treatment from one that does not.

Radiographs — showing decay beneath restorations, the quality of existing root fillings, and any change at the root tip. Tracing a sinus tract with a gutta-percha point on a radiograph identifies the source tooth directly.

CBCT imaging — increasingly useful in persistent cases, since it reveals missed canals, fractures and small lesions that two-dimensional films do not.

Bite assessment — heavy or off-axis loading contributes to cracks and to restoration failure.

Treatment depends on the cause, and the point of the assessment is to choose correctly.

Replacing the restoration where the margin has failed: removing it, removing the decay beneath, and restoring with a well-sealed replacement. Our white fillings and dental crowns pages cover the options.

Root canal treatment or retreatment where the pulp is involved. Retreatment means removing the existing root filling, locating and cleaning any missed anatomy, and re-sealing. Our root canal page explains the procedure, and our article on recovery after root canal treatment covers what follows.

Surgical endodontic treatment where retreatment is not possible or has not worked — treating the root tip directly through the gum.

Periodontal treatment where the source is a pocket rather than the tooth, as covered on our gum disease treatment page.

Correcting a contact point where food packing is the driver.

Extraction where the tooth is not restorable — most commonly with a vertical root fracture. Our article on crown versus extraction works through that decision.

Old dental work does not last indefinitely, and the practical measures are about catching deterioration before it becomes infection.

Attend regular examinations, with radiographs at the interval your clinician advises — decay beneath restorations is frequently invisible otherwise. Report symptoms early rather than waiting for them to resolve on their own. Clean thoroughly at restoration margins, where problems begin. Address grinding, which contributes to both cracks and restoration failure. And where several large old restorations are present, it is reasonable to plan their replacement deliberately rather than waiting for each to fail.

• Recurrent infection means a route in has not been closed, not that the infection was inadequately treated

• Antibiotics reduce symptoms without removing the source, so the cycle repeats

• Common causes are failing margins, cracks, incompletely treated root canals, periodontal pockets and food packing

• A recurring gum boil is a sinus tract and reliably indicates a chronic source

• Identifying the cause requires sensibility testing, radiographs and sometimes CBCT, not just examination

• Facial swelling, fever or difficulty swallowing require same-day assessment

Why do antibiotics only work temporarily?

Because they reduce the bacterial load without removing the physical source — a necrotic pulp, a space beneath a restoration, or a crack. Once the course finishes, the source repopulates. Antibiotics are appropriate alongside definitive treatment where infection is spreading, not instead of it.

Can decay under a crown be seen without an X-ray?

Often not. The crown covers the tooth, so decay at or beneath the margin may be entirely hidden. This is one of the main reasons radiographs are taken at intervals even when nothing is visible and nothing hurts.

Does a recurring gum boil mean the tooth needs removing?

Not necessarily. A sinus tract indicates a chronic source of infection, but many such teeth are successfully treated with root canal treatment, retreatment or surgical endodontic treatment. Whether the tooth is restorable depends on how much sound structure remains and whether a fracture is present.

Why did my root canal treatment fail?

Common reasons include a canal that was not located — some teeth have more canals than average — a canal that could not be fully cleaned because of curvature or calcification, degradation of the seal over time, or bacteria re-entering through a leaking restoration above the root filling. Retreatment addresses many of these.

Can a cracked tooth always be saved?

It depends on where the crack runs. A crack confined to the crown of the tooth can frequently be managed, often with a crown to hold the cusps together. A crack extending vertically down the root is generally not restorable, and the tooth requires removal.

How often should old fillings and crowns be checked?

At the interval your clinician recommends, which is based on your individual risk rather than a fixed rule. Radiographs are taken periodically because deterioration beneath restorations cannot be detected by examination alone.

If infection keeps returning to the same tooth, the useful step is a focused assessment to find the route in — sensibility testing, radiographs, and where necessary three-dimensional imaging — rather than another course of antibiotics.

You can contact our team to arrange an appointment at our Wimpole Street practice. Our emergency dentist page covers urgent care, and our root canal page explains treatment where the pulp is involved.

This article provides general information about recurrent dental infection and does not constitute individual dental advice. The source of infection can only be identified through clinical examination, sensibility testing and appropriate radiographs, and treatment varies considerably between cases. Anyone with facial swelling, fever, or difficulty swallowing or breathing should seek urgent medical or dental care. Wimpole Dental is regulated by the Care Quality Commission, and our clinicians are registered with the General Dental Council.

Next review due: 4 September 2027