Dental amalgam, often referred to as “silver fillings,” has been a common restorative material in dentistry for over 150 years. This durable substance is a mixture of metals, approximately 50% of which is elemental mercury by weight, combined with a powdered alloy composed mainly of silver, tin, and copper. Mercury is used because its unique liquid properties allow it to bind the metal powders together, creating a strong and long-lasting filling. A frequent concern is whether the material remains completely sealed or if its components can escape over time. The material does not “leak” liquid mercury, but the elemental mercury can be released from the hardened filling in other forms. This release is a known scientific phenomenon and is the focus of ongoing research and regulatory oversight.
How Amalgam Fillings Release Mercury Vapor and Particles
The release of mercury from a dental amalgam filling primarily occurs through two distinct mechanisms: the continuous emission of elemental mercury vapor and the generation of microscopic particulate matter. The term “leak” is misleading because the mercury is not escaping as a liquid; rather, it is a product of the material’s physical and chemical state. The elemental mercury within the filling is slowly released as an invisible, odorless gas known as mercury vapor, which can then be inhaled and absorbed through the lungs.
This continuous, low-level vaporization is influenced by the temperature of the filling’s surface. Even small fluctuations in temperature, such as those caused by consuming hot or cold beverages, can accelerate the rate at which mercury vapor is released. The other release pathway involves the physical wear of the filling material itself. Mechanical forces, like those from chewing or teeth grinding, cause friction and abrasion on the filling’s surface, which generates microscopic particles of the amalgam material. These minute particles can be swallowed and absorbed by the body through the digestive tract.
Common Activities That Increase Mercury Release
Several common activities and patient behaviors accelerate the rate at which mercury vapor and particles are released from amalgam restorations. Any action that increases the temperature or friction on the filling surface will temporarily elevate the emission rate.
- Mastication, or chewing food, is a primary factor due to repetitive friction and the force needed to break down food.
- Teeth grinding (bruxism) significantly increases mechanical wear and friction, leading to a greater release of particulate matter.
- Consuming hot liquids, such as coffee or soup, temporarily raises the amalgam’s temperature, increasing the vaporization of elemental mercury.
- The initial placement and subsequent removal of amalgam fillings can also temporarily result in a sharp, transient increase in mercury vapor exposure.
What Regulatory Bodies Say About Amalgam Safety
Major health organizations, including the U.S. Food and Drug Administration (FDA) and the American Dental Association (ADA), acknowledge the low-level release of mercury vapor from amalgam fillings. The FDA has concluded that, based on current scientific evidence, the exposure levels resulting from amalgam are generally considered safe for the majority of the population. They have stated that the evidence does not show that exposure from amalgam causes harmful health effects for most people.
The FDA recommends that certain vulnerable populations should avoid getting new amalgam fillings whenever possible and appropriate. This advisory includes:
- Pregnant women.
- Women planning to become pregnant.
- Nursing mothers.
- Young children.
- Individuals with pre-existing neurological disorders or impaired kidney function.
For the general population, these regulatory bodies agree that existing amalgam fillings that are in good condition should not be removed unless medically necessary, as the removal process itself can temporarily increase mercury vapor exposure.
Physical Signs That A Filling Needs Replacement
While the release of mercury vapor is an invisible process, there are practical, physical signs that an amalgam filling is structurally failing and needs dental intervention.
- The development of a crack, either in the filling itself or in the surrounding tooth structure, which compromises the filling’s seal.
- Secondary decay, which occurs when the seal between the filling and the tooth margin breaks down, allowing bacteria to infiltrate the space beneath.
- Visible signs of corrosion, such as significant darkening or tarnish on the filling’s surface, suggesting the material’s integrity is deteriorating.
- Increased sensitivity to hot or cold temperatures, or pain when chewing, which may signal that the filling is loose or the tooth pulp is exposed.