The question of whether to replace older “silver fillings,” formally known as dental amalgam, is a common dilemma that blends structural concerns with personal health considerations. These restorations have been a standard in dentistry for over a century due to their durability. However, their composition has led to a long-running debate about safety and health implications, prompting many patients to seek alternatives. The decision to remove and replace amalgam fillings should be informed by a clear understanding of both the clinical state of the existing filling and the scientific context of its materials. This article explores the factors that influence this complex decision.
Understanding Amalgam Fillings
Dental amalgam is a material used to fill cavities that consists of a mixture of liquid mercury and a powdered alloy of silver, tin, and copper. Amalgam fillings are often referred to as “silver fillings” because of their metallic color and high silver content. This material is known for its exceptional longevity and strength, making it particularly well-suited for high-pressure areas like the back molars. On average, amalgam restorations can last between 10 to 15 years, depending on factors like the patient’s oral hygiene and chewing forces. The material is initially soft, allowing it to be easily packed into the prepared tooth cavity, where it then hardens into a strong, stable structure.
The Clinical Necessity for Replacement
Many replacement recommendations are based purely on structural and functional issues. A primary reason for replacement is recurrent decay, which is new tooth decay forming underneath or around the edges of the existing filling. This occurs when a marginal breakdown creates microleakage, allowing bacteria and food debris to infiltrate the area between the filling and the tooth structure.
Another frequent cause for replacement is the fracture of either the filling itself or the surrounding tooth structure. Amalgam does not bond directly to the tooth, and as a metal, it can expand and contract slightly with temperature changes. This puts stress on the remaining tooth tissue over many years, potentially leading to structural fissures, especially in cases where the restoration is large. Amalgam fillings also require a certain bulk for retention, which means that their placement often requires the removal of more healthy tooth structure than modern bonded materials.
The Health Debate: Mercury Exposure
The core of the safety debate stems from the fact that dental amalgam is approximately 50% elemental mercury by weight. This elemental mercury continuously releases low levels of mercury vapor, which is the predominant form released from these fillings. Actions like chewing, brushing, and consuming hot liquids increase the rate of this vapor release.
The scientific consensus, held by bodies like the Food and Drug Administration (FDA), is that the levels of mercury released are generally not high enough to cause harm in the general population. The FDA classifies dental amalgam as a Class II device, concluding that the exposure is typically well below levels associated with adverse health effects. However, the FDA recommends against the use of amalgam in certain sensitive populations due to potential increased risk from mercury exposure. These specific groups include:
- Pregnant women
- Nursing mothers
- Children under the age of six
- People with pre-existing neurological diseases
- Those with impaired kidney function
- Individuals with a known allergy to mercury
Despite this, the ongoing debate and concern over mercury toxicity lead many patients to elect for replacement.
Safe Removal and Alternative Materials
For patients who choose to replace their amalgam fillings, specialized procedures have been developed to minimize exposure to mercury vapor during the removal process. The Safe Mercury Amalgam Removal Technique (SMART) is a set of safety protocols established to protect the patient, the dental team, and the environment. This technique includes using protective measures to isolate the tooth and contain the mercury released as the filling is drilled out.
Key steps in the SMART protocol involve:
- The use of a rubber dam made of non-latex nitrile to isolate the operational area.
- A high-volume suction system placed near the tooth to capture mercury vapor.
- An external air filtration system in the treatment room.
- Providing the patient with an alternative air source, such as a nasal mask delivering oxygen, to avoid inhaling any released vapors.
- Sectioning the amalgam into larger chunks before removal, reducing the amount of drilling and subsequent vapor generation.
Once the amalgam is safely removed, several alternative materials are available for the new restoration. Composite resin is the most common tooth-colored option, which bonds directly to the tooth structure, requiring less removal of healthy tissue than amalgam. Composite fillings typically last between five and ten years and offer a significant aesthetic advantage. For larger restorations, porcelain or ceramic inlays and onlays are often used, which are custom-made in a lab and offer excellent durability. Glass ionomer cements are another option, sometimes used for smaller, non-load-bearing areas, as they possess the unique property of releasing fluoride.