Dental amalgam, commonly known as a silver filling, is a restorative material used to fill cavities caused by tooth decay. It has been a standard treatment option for over 150 years due to its durability, strength, and relatively low cost. The material is mixed at the time of the procedure, allowing the dentist to pack the softened material into the prepared tooth structure before it quickly sets into a hard restoration.
Visual Characteristics of Amalgam Fillings
When first placed, a fresh amalgam filling exhibits a bright, metallic silver or silver-gray sheen. This initial appearance gives the restoration its popular name. However, this reflective surface is temporary because the metallic components react with the oral environment. Over time, the surface begins to tarnish and corrode due to exposure to saliva, food, and temperature changes.
This degradation process causes the filling to darken significantly. Older restorations often appear dark gray or nearly black, standing out distinctly against the natural tooth structure. The texture is opaque and entirely metallic, contrasting sharply with modern, translucent filling materials. Dentists typically reserve amalgam for posterior teeth, such as molars and premolars, where the dark color is less visible and the material can better withstand the heavy forces of chewing.
The Metallic Components of Amalgam
Dental amalgam is a unique alloy created by mixing liquid elemental mercury with a powdered metallic alloy. The term “amalgam” refers to any alloy that includes mercury in its composition. The alloy powder is primarily composed of silver, which makes up around 40% to 65% of the mixture, giving the filling its distinctive initial color.
Other significant metals in the powder include tin, which controls the setting reaction, and copper, which enhances the material’s strength and reduces corrosion. Elemental mercury constitutes approximately 50% of the final filling’s weight and serves a binding function. The liquid mercury chemically reacts with the solid alloy particles to create a plastic, moldable mass that hardens quickly.
Addressing Safety Concerns
The inclusion of elemental mercury in dental amalgam has been a source of public health concern for decades. Amalgam fillings release small amounts of elemental mercury vapor, particularly during chewing or when exposed to heat. The body absorbs this vapor through the lungs, leading to questions about the material’s long-term safety.
Major health organizations, including the U.S. Food and Drug Administration (FDA), have reviewed the scientific evidence and concluded that the amount of mercury vapor released is too low to cause adverse health effects in the majority of the population. However, the FDA recommends that certain high-risk groups avoid the placement of new amalgam fillings whenever possible, as they may be more sensitive to mercury exposure. The FDA identifies high-risk groups as:
- Pregnant women.
- Children under the age of six.
- People with pre-existing neurological diseases.
- People with impaired kidney function.
Modern Alternatives to Silver Fillings
Due to aesthetic concerns and public discussion about mercury, the use of dental amalgam has declined. The most common alternative is composite resin, often referred to as a tooth-colored or white filling. This material is made from a plastic acrylic resin matrix reinforced with fine glass particles.
Composite resins offer a significant aesthetic advantage as they can be precisely color-matched to the surrounding tooth, making the restoration virtually invisible. Another option is glass ionomer cement, a tooth-colored material that releases fluoride over time, offering added protection against decay. These modern materials bond directly to the tooth structure, allowing for a more conservative preparation that preserves natural tooth material.