Old Silver Filling Cracked or Leaking? When Should It Be Replaced?

If you have noticed sensitivity, a rough edge, or a slightly different taste when you bite down on a tooth with an old silver filling, you are not alone. Many adults in the UK have amalgam fillings that were placed years or even decades ago, and it is perfectly natural to wonder whether a cracked or leaking silver filling needs attention.

Silver amalgam fillings have been a reliable restorative material in dentistry for well over a century. However, like any dental restoration, they do not last indefinitely. Over time, the margins of a filling can begin to break down, the filling itself may crack, or the seal between the filling and the tooth may weaken—sometimes referred to as a "leaking" filling.

This article explains the common causes of filling failure, the symptoms to be aware of, what replacement options may involve, and how you can look after your existing restorations to help them last as long as possible.

"A cracked or leaking silver filling may need to be replaced when the seal between the filling and the tooth has broken down, allowing bacteria or moisture to reach the underlying tooth structure. A dentist can assess the filling during a clinical examination and recommend the most suitable course of action."

What Are Silver Amalgam Fillings?

Silver amalgam fillings are made from a mixture of metals, typically including silver, tin, copper, and mercury, which are combined to form a durable, hard-wearing material. They have been used in dentistry for over 150 years and remain one of the most extensively studied restorative materials available.

Amalgam fillings were particularly popular for restoring back teeth (molars and premolars) because of their strength and ability to withstand significant biting forces. The average lifespan of an amalgam filling can vary considerably—from around ten years to several decades—depending on factors such as the size of the filling, where it is in the mouth, the patient's bite, and their oral hygiene habits.

Why Do Old Silver Fillings Crack or Leak?

• Thermal expansion and contraction — Every time you eat or drink something hot or cold, the filling material expands and contracts slightly. Over many years, these repeated micro-movements can weaken the bond.
• Chewing forces — The back teeth endure significant pressure during normal chewing, which can cause small cracks to develop over time.
• Corrosion — Amalgam fillings can undergo a slow corrosion process in the moist oral environment.
• Tooth decay around the filling — If the seal at the edge of a filling breaks down, bacteria may enter the gap—a process often referred to as "leaking."
• Tooth fracture — In some cases, particularly with large fillings, the remaining tooth structure may weaken and develop cracks of its own.

Signs That Your Silver Filling May Need Attention

• Sensitivity to hot, cold, or sweet foods and drinks around a filled tooth that was previously comfortable
• Pain or discomfort when biting down on the affected tooth
• A visible crack or chip in the filling
• A rough or sharp edge that you can feel with your tongue
• Dark discolouration around the margins of the filling
• Food frequently getting trapped around a particular tooth
• A metallic taste in the mouth

The Science Behind Filling Failure

When a filling's marginal seal breaks down, a microscopic gap can develop. Oral bacteria, along with saliva and food particles, can penetrate this gap in a process known as microleakage. Once bacteria reach the dentine beneath the filling, secondary decay can develop. Because this decay occurs underneath an existing restoration, it may progress for some time before symptoms appear.

In more advanced cases, if decay reaches the pulp of the tooth, it may cause inflammation or infection, which could require more extensive treatment such as root canal treatment to preserve the tooth.

What Happens When a Silver Filling Is Replaced?

If your dentist determines that a filling needs to be replaced, the procedure typically involves carefully removing the old filling material, clearing away any decay, and placing a new restoration. Common alternatives include:

• Tooth-coloured composite resin fillings — Matched to the shade of your natural teeth and bonded directly to the tooth structure.
• Porcelain or ceramic inlays and onlays — Custom-made restorations recommended for larger cavities where additional strength is needed.
• Dental crowns — If the remaining tooth structure is significantly compromised, a dental crown may be recommended.

How to Help Your Fillings Last Longer

• Brush twice daily with a fluoride toothpaste, paying attention to the areas around your fillings.
• Clean between your teeth daily using interdental brushes or floss.
• Limit sugary and acidic foods and drinks, which contribute to tooth decay.
• Avoid using your teeth as tools — Opening packages, biting nails, or chewing on hard objects can stress fillings.
• Wear a mouthguard if you grind your teeth, as bruxism can accelerate wear on both fillings and natural teeth.
• Attend regular dental check-ups, which allow your dentist to monitor the condition of your fillings.

Frequently Asked Questions

How long do silver amalgam fillings typically last?

The lifespan varies depending on size, location, biting forces, and how well it is maintained. Many amalgam fillings can last between 10 and 20 years, and some may last considerably longer. Regular dental check-ups allow your dentist to monitor their condition over time.

Can a cracked silver filling cause an infection?

A cracked or leaking filling can create a pathway for bacteria to reach the tooth structure beneath the restoration. If bacteria penetrate deep enough to affect the inner pulp, this could potentially lead to inflammation or infection. The risk depends on the severity and how quickly it is identified and addressed.

Is it painful to have an old filling replaced?

Filling replacement is typically carried out under local anaesthetic, which numbs the area and helps ensure you remain comfortable. Most patients find the process straightforward and comparable to having a new filling placed.

Should I replace all my silver fillings at once?

There is generally no clinical need to replace silver fillings that are intact, well-sealed, and functioning properly. Replacement is typically recommended on a case-by-case basis when there is evidence of deterioration, cracking, leaking, or associated decay.

Are tooth-coloured fillings as strong as silver amalgam?

Modern composite resin materials have improved significantly and offer excellent durability for many types of restoration. For larger restorations or teeth subject to particularly heavy biting forces, your dentist may recommend alternative options such as ceramic inlays or crowns.

How can I tell if my filling is leaking if I have no symptoms?

Filling deterioration does not always cause noticeable symptoms in its early stages. This is one of the reasons why regular dental check-ups are so valuable. During an examination, your dentist can visually inspect your fillings, check the margins with dental instruments, and use radiographs to detect any hidden decay or gaps.

Dental symptoms and treatment options should always be assessed individually during a clinical examination.

This article is intended for general informational purposes only and does not constitute dental advice, diagnosis, or treatment recommendation. South Kensington Medical & Dental is regulated by the Care Quality Commission (CQC). All dentists are registered with the General Dental Council (GDC). Medical practitioners are registered with the General Medical Council (GMC).