7 Signs Your Old Dental Work Needs Replacing

Dental restorations — fillings, crowns, bridges, inlays, and onlays — are not permanent. They are designed to last as long as possible, and with good care, many do serve for a decade or more. But every restoration has a lifespan, and when that lifespan is approaching its end, the restoration will give you signals. The patients who recognise those signals early and act on them spend far less money and undergo far less complex treatment than those who wait until something breaks.

The problem is that most patients do not know what to look for. They assume that if a restoration is not causing pain, it must be fine. This assumption is wrong and it is expensive. Many failing restorations do not hurt until the situation has escalated to the point where the tooth underneath is already significantly damaged.

At Serenity International Dental Clinic, we see this scenario regularly — patients who present with a crown or filling that has been quietly failing for years, often requiring more extensive treatment than would have been needed at the first sign of trouble. This guide covers the seven warning signs that tell you an existing restoration needs professional evaluation — and likely replacement.

For a deeper understanding of why crowns fail, see our detailed post on 10 common reasons dental crowns fail. And if you are unsure whether you need a crown in the first place, our post on 8 signs you need a dental crown provides clear clinical criteria.

1. Visible Cracks or Chips in the Restoration

A crack in a crown, inlay, or veneer is not a cosmetic problem — it is a structural one. Dental ceramic and composite resin may appear solid, but once a crack develops, it propagates under the cyclical loading of chewing. What begins as a hairline fracture that your dentist can only see under magnification can progress to a complete fracture through the restoration, into the tooth beneath it, and in some cases down the root.

Why it happens: Dental ceramic is strong in compression but relatively brittle in tension. Occlusal overloading — whether from a bite that is slightly off, an opposing tooth that is very hard, or bruxism (teeth grinding) — creates tensile stresses at the internal surface of the restoration. Over time, these stresses exceed the material’s fatigue limit and a crack initiates.

What to look for: Run your tongue across the surface of your crowns and fillings. Any roughness, sharp edge, or notch that was not there before may indicate a crack or chip. Under good light with a mirror, visible line fractures in ceramic or composite restorations are visible as dark lines within the material. A tooth that bites and then releases with a sharp, localised pain — “cracked tooth syndrome” — is a classic sign of a crack propagating through the tooth structure itself beneath an existing restoration.

Why it matters: A cracked restoration allows bacteria direct access to the tooth and the cement layer. Secondary decay is almost inevitable without intervention. A crack that extends into the root may make the tooth non-restorable, necessitating extraction rather than replacement.

2. Dark Margin Around a Crown

A healthy crown margin — the border where the crown meets the tooth — should be essentially invisible: the tooth colour transitions to the crown colour with no gap, staining, or darkening visible at the gumline.

A dark line at the crown margin is a significant warning sign. It may indicate any of the following:

Cement washout: The luting cement that seals the margin has degraded or dissolved, leaving a gap between the crown and the tooth. This gap collects oral fluids, food debris, and bacteria. Secondary decay is already developing if washout has been present for months.

Metal show-through: Many older crowns are porcelain-fused-to-metal (PFM) restorations where a metal substructure sits beneath the porcelain layer. As gums recede with age, the metal margin — which was originally subgingival — becomes visible as a dark grey or black line at the gumline. This is primarily an aesthetic issue but signals that the crown is ageing and that gum recession may be compromising the margin seal.

Secondary decay: Dark brown or black discolouration at the margin that is not present along the entire circumference of the crown may indicate active decay penetrating at a specific margin point.

Practical action: A dark crown margin warrants a dental appointment. The dentist will probe the margin, take a periapical X-ray to assess for decay beneath the crown, and use transillumination or magnification to assess margin integrity. Early detection at this stage often means the crown can be replaced with a new one over a sound tooth — waiting until you have pain may mean the tooth requires root canal treatment or extraction.

3. Sensitivity Under an Existing Restoration

A tooth beneath a well-sealed, well-fitted restoration should not be sensitive. If a tooth with a crown or a large filling has started to react to cold drinks, sweet foods, or biting pressure in a way that it did not before, something has changed.

Cold sensitivity that resolves quickly (within three to five seconds of removing the stimulus) may indicate dentinal hypersensitivity from a compromised margin — bacteria have reached the dentin and irritated the dentinal tubules. This is typically reversible if caught early and the margin is resealed.

Cold sensitivity that lingers for more than thirty seconds after the stimulus is removed is a classic sign of irreversible pulpitis — the pulp (nerve) of the tooth is inflamed beyond recovery. This tooth will almost certainly require root canal treatment before a new crown can be placed.

Sensitivity to biting pressure that is sharp and localised often indicates either a cracked restoration, a cracked tooth beneath the restoration, or an abscess forming at the root apex. All three require prompt assessment.

Spontaneous pain — pain that occurs without any stimulus, especially at night — is a serious sign that pulpal involvement is advanced. This should not be left unassessed.

Do not dismiss sensitivity under existing restorations as “normal.” It is not. A tooth with a crown or filling that is functioning correctly should not be sensitive to routine stimuli.

4. Old Amalgam Fillings That Are Cracked or Leaking

Amalgam fillings — the silver-coloured metal fillings used almost universally before tooth-coloured composite became the standard — can be highly durable. Many amalgam fillings placed in the 1980s and 1990s are still functioning adequately today. However, amalgam ages in specific ways that require monitoring.

Marginal fracture: Amalgam is a rigid material that does not bond to tooth structure — it relies on mechanical undercut retention. Over years of thermal cycling (expansion and contraction from hot and cold foods) and functional loading, the margins of amalgam fillings fracture. This creates an irregular, open margin that is impossible to clean effectively and allows bacterial ingress.

Crazing of the surrounding tooth: Amalgam expands as it corrodes. In older fillings, this expansion gradually wedges the surrounding tooth structure apart, creating microcracks in the enamel and dentine that radiate outward from the filling. These cracks weaken the tooth structure and are pathways for bacterial penetration.

Corrosion products: Dark brown or black discolouration in the dentin surrounding an old amalgam filling is often corrosion staining — amalgam’s byproducts leaching into the tooth. While this staining does not itself indicate decay, it makes it very difficult to assess on X-ray whether decay is also present.

Practically: An old amalgam filling that shows visible marginal fracture on a dental radiograph, or that your dentist can probe a gap into, should be replaced. The decision of whether to replace with composite resin or cover the tooth with an inlay, onlay, or crown depends on how much sound tooth structure remains.

5. A Crown That Feels Loose or Rocks

A crown should feel identical to a natural tooth. It should not rock, flex, or shift when you apply finger pressure to its sides, and it should not feel different when you bite down compared to surrounding teeth.

Any mobility in a crown indicates that the cement seal has been compromised. This is almost always detectable before the crown fully dislodges — and the window between “slightly loose” and “crown fell off” is the ideal time to act.

Why it matters: A crown that is loose but still in place is a serious clinical concern. Every flex of the crown pumps oral fluids — loaded with bacteria — in and out of the gap between the crown and the tooth. Decay under a loose crown can progress extremely rapidly because bacteria are being actively forced into contact with unprotected dentin with every bite.

What you might feel: A slight “give” when pressing on the crown from the side. A very subtle rocking sensation when biting. A change in how the crown sounds when you tap on it (a hollow quality rather than a solid sound). Some patients also notice a slight movement when they floss around the crown — the crown shifts slightly as the floss is pulled.

What to do: Contact your dentist promptly if you notice any of these signs. Do not ignore a loose crown and hope it tightens itself — it will not. The longer it remains loose, the more decay will have progressed by the time it is seen clinically.

6. Bad Taste or Bad Breath From Around an Old Bridge

A dental bridge spans a gap left by one or more missing teeth, supported by crowns on the teeth adjacent to the gap. The false tooth (pontic) in the middle sits just above the gum tissue. This design creates a maintenance challenge: the area beneath the pontic and around the bridge margins must be cleaned with a floss threader or interdental brush, not just a regular toothbrush.

When this cleaning is missed — which is common, because the technique is not intuitive — food and bacteria accumulate beneath the pontic and within the embrasure spaces around the bridge margins. The result is a persistent bad taste and bad breath that no amount of mouthwash resolves.

But the problem goes beyond aesthetics. Bacterial accumulation beneath a bridge pontic:

• Causes progressive gum inflammation and recession beneath the pontic
• Creates an environment where the abutment teeth (the crowned teeth supporting the bridge) are susceptible to secondary decay, particularly at the margins
• Can lead to bone loss in the pontic site over time

When the bridge itself is the problem: An older bridge whose margins have opened due to cement washout or gum recession may trap food and bacteria in a location that simply cannot be cleaned by any at-home method. In these cases, the bridge needs to be replaced to restore a cleanable environment.

When the patient technique is the problem: A floss threader or a Superfloss product threaded beneath the bridge pontic, used daily, resolves the vast majority of bridge hygiene complaints. Our clinical team demonstrates this technique at every bridge placement and reviews it at hygiene appointments.

If you have a bridge and notice persistent bad taste or bad breath that seems localised to the bridge area, book an appointment. The earlier this is assessed, the more likely the abutment teeth can be preserved for a new bridge — rather than lost to the decay and bone loss that follow chronic bacterial accumulation.

7. An X-Ray Showing Decay Under a Restoration

This final sign is one that patients cannot detect themselves — it requires a dental X-ray. It is also, clinically, one of the most important early warning signs available.

Secondary decay — new cavity formation at the margins of or beneath an existing restoration — develops slowly and silently in most cases. By the time it causes sensitivity or pain, it has typically progressed through the dentin and is approaching the pulp. At that stage, what could have been a simple filling replacement requires root canal treatment and a new crown.

How it is detected: Bitewing X-rays — the standard X-rays taken at routine check-ups — show radiolucent (dark) areas at restoration margins that indicate demineralised tooth structure. A competent clinician reading a bitewing carefully can identify secondary decay at an early stage, often when the lesion is still in the outer third of dentin and can be managed with a straightforward replacement procedure.

Why routine X-rays matter: Patients who attend six-monthly check-ups and have regular bitewing X-rays (typically every twelve to eighteen months for adults at average cavity risk) have their secondary decay caught early almost without exception. Patients who do not attend regularly — or who decline X-rays — present with advanced lesions that are far more costly and invasive to treat.

This is one of the clearest arguments for consistent, preventive dental attendance. A bitewing X-ray that shows early decay under a filling, caught at a routine visit, results in a filling replacement that takes thirty minutes and costs a fraction of what root canal treatment and a crown would cost twelve months later.

The Right Time to Act Is Before Something Hurts

The seven signs in this guide — visible cracks, dark margins, sensitivity, ageing amalgam, loose crowns, bad taste from bridges, and X-ray findings — share one critical characteristic: they appear before the restoration fails completely and before the tooth beneath is catastrophically damaged.

Acting at the first sign of trouble is not over-treatment. It is the clinical equivalent of fixing a roof before the leak reaches the interior — the repair is smaller, cheaper, and far less disruptive than the restoration required after structural failure.

If you recognise any of these signs in your own mouth, book an evaluation at Serenity International Dental Clinic. Bring any previous X-rays or dental records if you have them. Our team will assess every existing restoration, identify any that are approaching failure, and discuss your options clearly — including which can be monitored and which need attention now.

Visit our dental crown service page to learn more about our approach to crown replacement and restoration, and our post on 10 common reasons dental crowns fail for the technical background behind crown longevity.