Electricity is produced because the Volta potential between the two metal plates makes electrons flow from the zinc to the copper and corrode the zinc.The non-magnetic character of zinc and its lack of color in solution delayed discovery of its importance to biochemistry and nutrition. This changed in 1940 when carbonic anhydrase, an enzyme that scrubs carbon dioxide from blood, was shown to have zinc in its active site. The digestive enzyme carboxypeptidase became the second known zinc-containing enzyme in 1955. Production
Mining and processing
Zinc is the fourth most common metal in use, trailing only iron, aluminium, and copper with an annual production of about 13 million tonnes. The worlds largest zinc producer is Nyrstar, a merger of the Australian OZ Minerals and the Belgian Umicore. About 70% of the worlds zinc originates from mining, while the remaining 30% comes from recycling secondary zinc. Commercially pure zinc is known as Special High Grade, often abbreviated SHG, and is 99.995% pure.Worldwide, 95% of new zinc is mined from sulfidic ore deposits, in which sphalerite (ZnS) is nearly always mixed with the sulfides of copper, lead and iron. : 6  Zinc mines are scattered throughout the world, with the main areas being China, Australia, and Peru. China produced 38% of the global zinc output in 2014.Zinc metal is produced using extractive metallurgy.
However, only in 3.6–7% will this be of sufficient severity to trigger the individual to seek medical advice.For unknown reasons, females are more likely to be affected than males, in a ratio of about 2:1, although others report this ratio to be as high as 9:1. Females are more likely to request treatment for TMD, and their symptoms are less likely to resolve. Females with TMD are more likely to be nulliparous than females without TMD. It has also been reported that female caucasians are more likely to be affected by TMD, and at an earlier age, than female African Americans.According to the most recent analyses of epidemiologic data using the RDC/TMD diagnostic criteria, of all TMD cases, group I (muscle disorders) accounts for 45.3%, group II (disc displacements) 41.1%, and group III (joint disorders) 30.1% (individuals may have diagnoses from more than one group). Using the RDC/TMD criteria, TMD has a prevalence in the general population of 9.7% for group I, 11.4% for group IIa, and 2.6% for group IIIa. History
Temporomandibular disorders were described as early as ancient Egypt. An older name for the condition is "Costens syndrome", eponymously referring to James B. Costen. Costen was an otolaryngologist, and although he was not the first physician to describe TMD, he wrote extensively on the topic, starting in 1934, and was the first to approach the disorder in an integrated and systematic way. Costen hypothesized that malocclusion caused TMD, and placed emphasis on ear symptoms, such as tinnitus, otaglia, impaired hearing, and even dizziness.