History and Background of Dental Amalgam
- Dental amalgam was used in the Tang dynasty in China and in Germany by Strockerus in the 16th century.
- The use of amalgams may date even earlier in the Tang dynasty.
- Amalgam was introduced to the Western world in the 19th century and faced controversies due to its mercury content.
- Polish-Jewish dentists brought amalgam to the United States in 1833, but faced backlash and had to flee.
- The use of amalgam caught on and by 1844, half of all dental restorations in upstate New York consisted of amalgam.
Composition and Properties of Dental Amalgam
- Dental amalgam is made by mixing liquid mercury with an alloy of silver, tin, and copper particles.
- The composition of the alloy particles is controlled by ISO standards.
- Amalgam is used for direct, permanent, posterior restorations and large foundation restorations.
- The reaction between mercury and alloy is called an amalgamation reaction.
- Alloy powder is mixed with liquid mercury to produce dental amalgam.
- Amalgam expands slightly on setting.
- Amalgam is a mixture of metals with mercury, with major components being silver, tin, and copper.
- The composition of the alloy powder is controlled by ISO standards.
- Amalgam is subject to plastic deformation or creep under intra-oral stresses.
- The γ2 phase of amalgam is responsible for high values of creep.
- Corrosion can occur in dental amalgam due to the presence of electrolytes.
Corrosion and Mechanical Properties
- Amalgam can contribute as an anode or cathode with saliva as electrolytes.
- Corrosion significantly affects the structure and mechanical properties of dental amalgam.
- The γ2 phase in conventional amalgam is the most reactive and forms an anode, leading to corrosion and release of mercury.
- Copper-enriched amalgams have lower corrosion rates compared to conventional amalgam.
- Corrosion products gather at the tooth-amalgam interface, reducing microleakage.
- Amalgam restorations develop strength slowly and may take up to 24 hours to reach a high value.
- Patients should avoid applying undue stress to freshly placed amalgam fillings.
- Amalgam restorations are brittle and susceptible to corrosion.
- Strength of set amalgam depends on alloy composition, particle size, shape, and distribution.
- Heat treatment controls the characteristic properties of the amalgam.
Liners and Bases
- A protective layer or liner should be placed prior to amalgam placement to reduce post-operative sensitivity.
- Different lining materials containing zinc, such as zinc oxide eugenol, zinc phosphate, glass ionomer cement, zinc poly-carboxylate, and resin, can be used.
- Liners act as a buffer and provide a good marginal seal for the amalgam restoration.
- Liners help to seal dentinal tubules and improve the longevity of the restoration.
- The use of liners is recommended to enhance the success of amalgam restorations.
- Varnish can be applied to the cavity wall to provide a good marginal seal.
- The varnish should be insoluble in water and composed of a resin in a volatile solvent.
- The solvent evaporates, leaving the resin behind to seal the dentinal tubules.
- Sealing the cavity with varnish helps to prevent microleakage and improve the longevity of the amalgam restoration.
- Proper sealing techniques contribute to the success of amalgam restorations.
Dental Amalgam Toxicity and Environmental Impact
- Concerns have been raised about potential mercury poisoning from dental amalgam.
- Major health and professional organizations consider amalgam safe, but questions have been raised.
- Acute allergic reactions to amalgam have been reported, although they are rare.
- Studies on mercury vapor and dental amalgam have provided insufficient information for definitive conclusions.
- Research gaps exist regarding potential neurotoxic and neuropsychological effects, co-exposure to mercury and methylmercury, and other occupational health effects.
- Dental amalgam is considered relatively safe in low doses.
- Amalgam vapor release through chewing is minimal and not considered a health risk.
- Patients may develop allergic reactions to amalgam, and alternatives like resin composite, glass ionomer cements, and ceramic or gold inlays can be used.
- Electromagnetic fields generated by MRI machines can increase mercury release, but the amount is not believed to pose a health risk.
- Amalgam waste should be properly separated and disposed of to prevent environmental contamination.
- In the United States, dental offices are prohibited from disposing of amalgam waste down the drain.
- Dental offices are required to use amalgam separators to capture and recycle the waste material.
- The U.S. Environmental Protection Agency (EPA) promulgated effluent guidelines in 2017 to regulate dental amalgam waste disposal.
- The European Commission has classified amalgam waste as hazardous and requires the use of amalgam separators in dental practices.
- Proper disposal of amalgam waste is necessary to prevent mercury contamination in the environment.
In dentistry, amalgam is a liquid mercury and metal alloy mixture used to fill cavities caused by tooth decay.
Dental amalgams were first documented in a Tang dynasty medical text written by Su Gong (苏恭) in 659, and appeared in Germany in 1528. In the 1800s, amalgam became the dental restorative material of choice due to its low cost, ease of application, strength, and durability.
