Dental amalgam is a mixture of metals consisting of liquid mercury and a powdered alloy composed of silver, tin, and copper. Approximately half of dental amalgam is elemental mercury by weight. The chemical properties of elemental mercury allow it to react with and bind together the silver, copper, and tin alloy particles to form an amalgam.
Benefits of Dental Amalgam
Dental amalgam is strong and long-lasting, so they are less likely to break than some other types of fillings.
They are useful in patients that have a high risk of tooth decay
Amalgam restoration are used in condition where moisture makes it difficult for other materials such as resins cements to establish a bond to tooth.
Amalgam fillings are the least expensive type of filling material.
They are used in large cavity preparation
Plastic deformation or creep happens when subjected to intra-oral stresses such as chewing or grinding. Creep causes the amalgam to flow and protrudes from the margin of the cavity forming unsupported edges. The ditch is formed around the margins of the amalgam restoration after fracture due to amalgam creep at the occlusal margins and it is considered one of the properties of dental amalgam.
Dental amalgam also have corrosive properties. Corrosion occurs when an anode and cathode are set up in the presence of electrolytes, creating an electrolytic cell and the multiphase structure of dental amalgam can contribute as an anode or cathode with saliva as electrolytes. Corrosion may significantly affect the structure and mechanical properties of set dental amalgam restoration. In conventional amalgam, y2 phase is the most reactive and readily forms an anode which will break down releasing corrosion products and mercury. Some amount of the mercury will combine rapidly with unreacted alloy and some will be ingested. The chances of ditching are further increased and Copper-enriched amalgams contain little or no y2 phase. The copper–tin phase, which replaces y2 in these materials, is still the most corrosion prone phase in the amalgam. The corrosion however is still much lower than conventional amalgam. The corrosion products will gather at the tooth-amalgam interface and fill the micro gap or also called as marginal gap which helps to decrease micro leakage. Micro leakage is the leakage of minute amounts of fluids or liquids, debris, and microorganisms through the microscopic space between a dental restoration and the adjacent surface of the cavity preparation. Micro leakage may risk recurrent caries.
Risks related to Dental Amalgam
- It contains elemental mercury and releases low levels of mercury in the form of a vapor that can be inhaled and absorbed by the lungs. Exposure to the high levels of mercury vapor, which may occur in some occupational settings, has been associated with adverse effects in the brain and the kidney also.
- The children or infants may be more sensitive to the neurotoxic effects of mercury vapor.
Although the available evidence does not show that exposure to mercury present in dental amalgam will lead to adverse health effects in the general population, exposure to mercury may pose a greater health risk in the groups of people listed below, who may be more susceptible to potential adverse effects generally associated with mercury.
Pregnant women and their developing fetuses
Women who are planning for conceiving
Nursing mothers and their newborns and infants
Children who younger than six years of age
People with pre-existing neurological diseases
People with impaired kidney functions or any kidney related diseases
People with known sensitivity or allergies to mercury or other components present in dental amalgam.
Why mercury used in dental amalgam?
Approximately half of a dental amalgam is composed of liquid mercury and the other half is composed of powdered alloy of silver, tin, and copper. Mercury is used to bind the alloy particles together into a strong, durable, and solid filling and mercury’s unique properties make it an important component of dental amalgam that contributes to its durability. It is a liquid at room temperature that bonds well with the alloy powder which is the unique property of the mercury. There are several chemical forms of mercury i.e. elemental mercury, inorganic mercury, and methyl mercury. The form of mercury associated with dental amalgam is elemental mercury, which releases mercury vapors. Mercury vapor is mainly absorbed by the lungs and methyl mercury is mainly absorbed through the digestive tract. The body processes these forms of mercury differently and has different levels of tolerance for mercury vapor and methyl mercury.
Bioaccumulation refers to the building up or steadily increasing concentration of a chemical in organs or tissues in the body. Mercury from dental amalgam and other sources is also bioaccumulative. Although much of the mercury either from dental amalgam is eliminated, a part of it can accumulate in the bodily fluids and tissues including the kidneys and brain. However, studies have not shown that increased mercury levels and bioaccumulation due to dental amalgam fillings result in detectable damage to target organs.
Mercury poisoning is a type of metal poisoning due to exposure to mercury vapors. The symptoms depend upon the type, dose, method, and duration of exposure to mercury. They may include muscle weakness, poor coordination, numbness in the hands and feet, skin rashes, anxiety, memory problems, trouble speaking, trouble hearing, or trouble seeing, etc. High-level exposure to methyl mercury is known as
Minamata disease. Methyl mercury exposure in children may result in
acrodynia also called as pink disease in which the skin becomes pink and peels off on its own. Long-term complications may include kidney problems and decreased intelligence also.