Dental fillings are a common restorative procedure used to treat tooth decay. For over a century, the most prevalent material used has been the metallic restoration often called the “silver filling.” This material is not pure silver but a mixture of metals known formally as dental amalgam. It is a highly durable and cost-effective option that has long been the standard for repairing cavities, particularly in the back teeth. Its composition has led to ongoing discussion and significant advancements in alternative dental materials.
The Material: Defining Dental Amalgam
Dental amalgam is an alloy created by mixing liquid elemental mercury with a powdered alloy comprised primarily of silver, tin, and copper. The final hardened filling material is approximately 50% elemental mercury by weight, blended with the powdered metals immediately before use. The powdered alloy typically contains 40% to 70% silver, and 12% to 30% each of tin and copper.
The process of mixing the liquid mercury with the powdered alloy is known as amalgamation. This reaction forms a soft, workable paste that is compressed into the cavity preparation. As the material sets, the mercury chemically reacts with the silver and tin to form a stable, hard compound. This finished amalgam is a dense crystalline structure robust enough to withstand the forces of chewing.
The Role and Durability of Amalgam
Amalgam became the restorative material of choice due to its high resistance to wear and fracture. This makes it well-suited for restoring molars and premolars, which bear the brunt of heavy chewing forces. Clinical studies have demonstrated the superior longevity of amalgam, with restorations often lasting 10 to 15 years or more.
Placing an amalgam filling is less sensitive to moisture contamination than other options, simplifying the procedure and reducing chair time for the patient. This lower technique sensitivity contributes to a predictable clinical outcome. Furthermore, amalgam is generally more cost-effective than alternative materials, making it an accessible option for many patients seeking long-lasting dental care.
Understanding the Mercury Controversy
The presence of elemental mercury in dental amalgam has long been the focus of public health discussion. The primary concern revolves around the release of mercury vapor, a colorless and odorless gas, which occurs in small amounts from the filling over time. Actions such as chewing, grinding, or professional placement and removal can temporarily increase the rate of this vapor release.
The body absorbs this elemental mercury vapor primarily through inhalation; it is distinct from the organic methylmercury found in fish. Regulatory bodies like the U.S. Food and Drug Administration (FDA) maintain that the small amount of vapor released is not associated with harmful health effects for most people. However, the FDA advises specific populations to avoid amalgam whenever a suitable alternative is available:
- Women who are pregnant, planning to become pregnant, or nursing.
- Children, particularly those under the age of six.
- People with pre-existing neurological diseases, such as Parkinson’s or multiple sclerosis.
- Those with impaired kidney function.
Modern Alternatives to Silver Fillings
The aesthetic drawbacks and public concerns surrounding amalgam have driven the widespread use of modern alternatives. The most common is the resin composite, often called a “tooth-colored filling,” which is a mixture of plastic and powdered glass filler. Composites offer significant aesthetic advantages as they can be precisely matched to the natural tooth shade, making them nearly invisible.
While composites have improved, they traditionally have a shorter lifespan than amalgam, often lasting 7 to 10 years. Their placement is also more demanding, requiring meticulous moisture control and a bonding process. Other alternatives include gold restorations, which are highly durable but significantly more expensive, and glass ionomer cements. Glass ionomer materials are weaker and reserved for non-load-bearing areas, but they offer the benefit of releasing small amounts of fluoride, which may help prevent further decay.