Dental amalgam controversy demonstrated that mercury released from amalgam restorations does not give rise to toxic effects on the nervous system of children. More recently, a Cochrane Systematic review in 2014 found, "insufficient evidence to support or refute any adverse effects associated with amalgam or composite restorations." Those opposed to dental amalgam suggest that mercury from dental amalgam may lead to nephrotoxicity, neurobehavioural changes, autoimmunity, oxidative stress, autism, skin and mucosa alterations, non-specific symptoms and complaints, Alzheimer's disease, and multiple sclerosis. Both those opposed and those not opposed to dental amalgam recognize that amalgam has been found to be a rare contributor to
Chemical element whole number. For example, the relative atomic mass of chlorine is 35.453 u, which differs greatly from a whole number as it is an average of about 76% chlorine-35 and 24% chlorine-37. Whenever a relative atomic mass value differs by more than 1% from a whole number, it is due to this averaging effect, as significant amounts of more than one isotope are naturally present in a sample of that element. Chemists and nuclear scientists have different definitions of a "pure element". In chemistry, a pure element means a substance whose atoms all (or in practice almost all) have the