Dental amalgam is a time-tested restorative material used for over 150 years. Often referred to as “silver fillings,” this durable mixture of metals creates a strong, hard substance capable of withstanding the significant forces of chewing. The longevity and affordability of amalgam restorations have made them a staple in dentistry. This material fills a prepared cavity, effectively sealing the tooth against further bacterial invasion and restoring its structure.
Composition and Placement of Amalgam
Dental amalgam is an alloy created by mixing liquid elemental mercury with a finely powdered metal mixture. The powdered component (amalgam alloy) typically consists of silver, tin, and copper; high-copper alloys are the modern standard due to improved strength and durability. Liquid mercury constitutes approximately 42% to 50% of the final mixture, acting to bind the alloy particles together into a workable mass.
The mixing process, called trituration, is often done mechanically in a sealed capsule. This results in a putty-like substance that a dentist quickly packs into the prepared cavity. The material is then carved to match the natural contours of the tooth before it rapidly sets and hardens. Because amalgam does not chemically bond to the tooth structure, the cavity preparation must be designed with specific shapes, known as undercuts, to lock the filling into place.
Key Advantages and Disadvantages
Amalgam’s advantage lies in its durability and resistance to wear, particularly in the demanding environment of the back molars. These restorations can last 10 to 15 years or longer. Amalgam is more cost-effective than many other restorative materials, and its placement is relatively quick and less sensitive to moisture contamination.
The material’s metallic, silver-gray appearance is a drawback. To ensure the filling is mechanically retained, a dentist must remove more healthy tooth structure than is required for materials that bond directly to the tooth. Patients may also experience thermal sensitivity to hot or cold temperatures shortly after placement, though this resolves over time.
The Safety Debate and Mercury Content
Elemental mercury in amalgam is the focus of a public debate regarding potential health effects. While the mercury is chemically bound within the filling structure, trace amounts of mercury vapor are released, particularly during activities like chewing or grinding teeth. The elemental mercury is a known neurotoxin, and the vapor can be absorbed through the lungs.
Regulatory bodies, including the U.S. Food and Drug Administration (FDA), generally consider the levels of mercury exposure from amalgam safe. However, the FDA advises against its use in certain high-risk populations due to bioaccumulation: pregnant women, nursing mothers, children, and people with pre-existing neurological disorders or impaired kidney function. Environmental groups have also pointed to mercury pollution from dental clinic waste disposal and cremation, prompting stricter regulations on waste management.
Alternatives to Amalgam Fillings
Several alternatives exist for restoring decayed teeth, offering varying trade-offs in aesthetics and durability. Composite resin is the most common substitute, offering a tooth-colored option. Composite requires less removal of healthy tooth because it bonds directly to the surface, but it is less durable than amalgam and its placement is more sensitive to moisture.
Glass ionomer cement is often used for smaller restorations or areas not subjected to heavy chewing forces. This material releases small amounts of fluoride, which may help protect the tooth from further decay. Gold or ceramic inlays and onlays offer high durability, but they are more costly indirect restorations custom-made in a lab.