Morbius
you've put forth the chlorine analogy to dismiss the assertion (and proven fact) that mercury vapor(and particles) do indeed escape from amalgams and that the mercury is somehow rendered non toxic. Please read this scientific rebuttal
Chemical Description of Amalgam
Mercury, including properties related to its toxic effects, is one of the most studied chemical substances.11,60,86 Historically, it was argued that the mercury in dental amalgam is bound in such a way as to render it safe. This argument is still made by members of the dental community supporting the continued use of dental amalgam.
An analogy between dental amalgam and table salt, often made by dental associations, was repeated at the FDA panel meeting during the public presentations by Dr. Dennis Charlton, president-elect of the Pennsylvania Dental Association.
The mercury in silver-colored restorations is bound in a molecular form in much the same manner as elemental chlorine gas is bound in the molecule of sodium chloride. And I'm sure most of you realize sodium chloride is simple table salt and that chlorine gas is poisonous. The molecule, the molecular combination of sodium and chloride makes it safe to be used in cooking and as a table spice.
Sodium chloride illustrates how toxic substances can be combined to create substances that are less toxic. Chemical descriptions of amalgam and table salt, however, are quite different. Chemically, mercury salts and sodium chloride are compounds, while amalgam, like salt water, is a mixture. Solutions, suspensions, colloids and alloys are types of mixtures; amalgam is an alloy. Compounds tend to be more tightly bound than mixtures and usually maintain stoichiometry. Table salt, an ionic solid, is always 50% sodium and 50% chlorine, but any amount of salt may be mixed with water until the solution saturates. Similarly, you can have varying amounts of mercury in amalgam. Unlike aqueous solutions (salt water), chemical reactions occur in forming amalgam creating chemical bonds between the mercury and other metals called intermetallic compounds. However, considering the lesson of mercury salts, one cannot draw a conclusion regarding the toxicity of a substance based on the existence of chemical bonds or by analogy with another substance.
Amalgam, by definition, is an alloy containing mercury and other metals. Alloys are mixtures of elements and compounds, typically metals, forming a metallic matrix. Alloys, like bronze and steel, have physical, mechanical and corrosion properties that are tailored by composition and fabrication processes. The amount of mercury escaping from amalgam can be determined experimentally. The release mechanisms, as vapor or through corrosion, and the amount released may depend on alloy composition and fabrication processes.
In 1895 the alloy composition of amalgam was standardized to what is called the gamma-2-phase amalgam which is formed by mixing about 50% liquid mercury with a powder containing 60% silver, 29% tin, less than 6% copper and less than 2% zinc.21 The material is an effective restoration material but develops binary phase regions including silver-mercury gamma-1 regions and tin-mercury gamma-2 regions. The difference in electrochemical potential between the two regions results in crevice corrosion.
In 1962, a new composition was developed where the metallic powder contains significantly more copper 12% to 30%. The gamma-2 phase tin-mercury regions are replaced by the formation of tin-copper regions. The reduced-gamma-2-phase or “high copper” amalgams are less expensive and have better corrosion and mechanical properties than the low-copper predecessor. The alloy composition for high-copper amalgam depends on the manufacturer with silver ranging from 40% to 70%, tin 12% to 30% and copper from 12% to 30% in the powder.21 Deepening on the formulation, the amount or mercury used can also vary from ~40% to ~50%. Some manufacturers also add smaller amounts of indium, zinc and/or palladium. Zinc is added to prevent oxidation of the other metals which keeps the alloy from turning dark.
http://www.iaomt.org/articles/files/files337/Cartland%20-US%20Dental%20Amalgam%20Debate%202010%20FDA%20Meeting%20-DRAFT%202011-03-28.pdf
