Amalgam (dentistry)
[1] It is made by mixing a combination of liquid mercury and particles of solid metals such as silver, copper or tin.
It remains soft for a short while after mixing, which facilitates it being snugly packed into the cavity and shaped before it sets hard.
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.
[2][3] In the 1800s, amalgam became the dental restorative material of choice due to its low cost, ease of application, strength, and durability.
[4] There are, according to Geir Bjørklund, indications that dental amalgam was used in the first part of the Tang dynasty in China (AD 618–907), and in Germany by Strockerus in about 1528.
[2] Evidence of a dental amalgam first appears in the Tang dynasty medical text Xinxiu bencao (新修本草) written by Su Gong (苏恭) in 659, manufactured from tin and silver.
[12][11] In 1962 a new amalgam alloy, called Dispersalloy, was introduced by William and Ralph Youdelis of Edmonton, Alberta, Canada.
10 years later, another alloy, called Tytin, was introduced by adding significant amount of Cu3Sn together with Ag3Sn, in the form of a unicompositional spherical particle to eliminate the γ2 phase.
[12] Dental amalgam is produced by mixing liquid mercury with an alloy made of silver, tin, and copper solid particles.
More recently (post-1986), there has been a change in the compositional standard of the alloy due to better understanding of structure-property relationships for the materials.
The corrosion products will gather at the tooth-amalgam interface and fill the microgap (marginal gap) which helps to decrease microleakage.
[11] Microleakage is the leakage of minute amounts of fluids, debris, and microorganisms through the microscopic space between a dental restoration and the adjacent surface of the cavity preparation.
An amalgam restoration develops its strength slowly and may take up to 24 hours or longer to reach a reasonably high value.
At the time when the patient is dismissed from the surgery, typically some 15–20 minutes after placing the filling, the amalgam is relatively weak.
[11] Therefore, dentists need to instruct patients not to apply undue stress to their freshly placed amalgam fillings.
[12] The fact that tin had a greater affinity for copper than for mercury meant that the gamma-2 phase was reduced or eliminated.
[12] The dissolved tin migrates to the outside of the silver-copper particles to form Cu6Sn5, the eta prime (η′) phase of the copper-tin system.
However, there is low-quality evidence in two 2014 studies [28][29] to suggest that resin composites lead to higher failure rates and risk of secondary caries than amalgam restorations.
[28] Though, there is insufficient evidence to support or refute any adverse effects amalgam may have on patients, new research is unlikely to change opinion on its safety and due to the decision for a global phase-down of amalgam (Minamata Convention on Mercury) general opinion on its safety is unlikely to change.
The New England Children's Amalgam Trial (NECAT), a randomized controlled trial, yielded results "consistent with previous reports suggesting that the longevity of amalgam is higher than that of resin-based compomer in primary teeth, according to a 2007 review of the study,[22] with some similar claims in a 2003 paper,[30] and composites in permanent teeth according to that 2007 review [22] and a paper from 1986.
These situations would include small occlusal restorations, in which amalgam would require the removal of more sound tooth structure,[32] as well as in "enamel sites beyond the height of contour".
[34] He recommended that the prepared cavity be coated with zinc phosphate cement just prior to filling with amalgam, in order to improve the seal and retention.
According to R. Weiner, a protective layer or liner should be placed prior to the placement of amalgam to act as a buffer, helping to reduce sensitivity to the tooth.
Major health and professional organizations regard amalgam as safe[1][45][46] but questions have been raised[47] and acute but rare allergic reactions have been reported.
[48] Critics argue that it has toxic effects that make it unsafe, both for the patient and perhaps even more so for the dental professional manipulating it during a restoration.
[52] With regard to amalgam placement and removal in pregnancy, research has not shown any adverse effects for the mother or fetus.
[51] In response to The Minamata Convention on Mercury, the European Commission has confirmed its position that individual nations should work to gradually scale down the use of dental amalgam.
The wastewater is sent to the local sewage treatment plant, which is not designed to treat or recycle mercury or other heavy metals.
As the milk teeth won't remain for long, the avoidance of amalgam for children is driving by environmental considerations.
[62] Some individuals have a sensitivity to amalgam and may develop oral lesions in which case a change of filling type is recommended.
