They are composed of 55% mercury, the most toxic metals on Earth. Scientific research demonstrates that dental mercury amalgam exposes dental professionals, dental staff, dental patients, and fetuses to releases of mercury vapor, mercury-containing particulate, and/or other forms of mercury contamination. Mercury vapor is known to be released from dental mercury amalgam fillings at higher rates during brushing, cleaning, clenching of teeth, chewing, and mercury is also known to be released during the placement, replacement, and removal of dental mercury amalgam fillings. Essentially, an unsafe amalgam removal process releases mercury vapor and particles that can be harmful to the patient, the dentist, the dental staff, and the environment. In 2008, the European Commission asserted that there is no evidence showing negative effects on the human central nervous system when applying amalgam fillings as reported in previous studies. In 2009, a similar statement was made by the American Dental Association.