Mercury is a naturally occurring element, with the chemical symbol Hg. Located in the d-block of the periodic table, in group 12 of the periodic table and in period 6. Mercury has an atomic number (number of protons) of 80 and standard relative atomic mass of 200.592 (combined mass of protons and neutrons).  Mercury which appears as a silvery liquid at 20°C, due to its melting point of −38.829°C.  Due to its unusual properties, mercury has a wide range of medical applications.
Due to the toxicity of mercury, many of the uses and applications of it are seen as controversial. One of the most common uses of mercury in history is in glass thermometers. Due to its low melting point, meaning it is a liquid at room temperature alongside its ability to undergo thermal expansion, mercury has been used in thermometers for hundreds of years. Although due to toxicity many countries are trying phase out the use or ban the use of mercury in thermometers.
Another use of a mercury alloy is in dental amalgams. The process is used to fill in cavities caused by tooth decay, which is often the result of the release of plaque build up. This medical treatment has been used for 150 years but again ,due to concerns over toxicity, it is being phased out. 
- ↑ NIST. Atomic Weights and Isotopic Compositions for Mercury. 2009 [03/12/16]. Available at: http://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=hg
- ↑ Royal Society of Chemistry . Mercury. 2016 [03/12/16. Available at: http://www.rsc.org/periodic-table/element/80/mercury
- ↑ Rathore M, Singh A , Pant VA. The Dental Amalgam Toxicity Fear: A Myth or Actuality. Toxicological International 2012;19:81–88.