Dental amalgam is a restorative material used by dentists to repair cavities caused by decay. Commonly known as a “silver filling,” this durable substance is formed by mixing a liquid metal with an alloy powder. It has been a preferred choice for posterior restorations due to its strength and ability to withstand the heavy forces of chewing. The material is placed into the prepared tooth cavity, where it hardens into a solid mass.
The Distinct Visual Appearance of Amalgam
A newly placed amalgam filling has a bright, metallic appearance, often described as shiny silver or light gray. This initial polished sheen makes the restoration noticeable against the natural tooth enamel and dentin. Because amalgam restorations are not color-matched, they create a stark contrast, particularly when a person laughs or opens their mouth wide. The material is opaque, meaning light cannot pass through it.
Over time, the filling’s visual characteristics change due to exposure to saliva, food, and temperature fluctuations. This causes the metal surface to tarnish and oxidize. The color gradually shifts from bright silver to a dull, dark gray or nearly black. This darkening is a normal chemical reaction and does not necessarily indicate a failure of the restoration, but it increases the filling’s visibility.
The Material Composition
The metallic color of a silver filling results from its composition, which is an alloy of several different metals. The term “amalgam” refers to any alloy that includes elemental mercury. Mercury serves as the liquid component that binds the other powdered metals together, and the final hardened filling is typically composed of about 50% elemental mercury by weight.
The remaining 50% is the powdered alloy, primarily composed of silver, tin, and copper. Silver is the largest component (40% to 70%), contributing to the initial silver hue and the material’s strength. Copper (12% to 30%) is added to reduce corrosion and improve overall strength. Tin reacts with the mercury to help form the hardened structure of the filling.
Comparing Amalgam to Tooth-Colored Alternatives
The visual difference between an amalgam filling and modern tooth-colored alternatives is substantial. The most common alternative, composite resin, is a mixture of plastic and fine glass particles formulated to match the exact shade of the surrounding tooth structure. This allows the composite material to blend in seamlessly. Composite resin also possesses a degree of translucency, which mimics the way natural tooth enamel interacts with light.
Amalgam is a dark, opaque material that reflects light differently than natural enamel. While composite resin is designed for aesthetic harmony, the amalgam filling is designed to be strong and durable in high-stress areas. The choice between the two materials often comes down to aesthetic preference. For this reason, amalgam fillings are almost always limited to the posterior teeth, where they are less visible when a person smiles.