Exposure
The amount of mercury patients are subjected to is itself controversial. Many studies have been conducted and findings have varied substantially. Depending on the study, average systemic uptake levels have been estimated to range between 1.7 µg/day and 17 µg/day.
As a (straight) comparison, these daily absorption levels comprise between 3.4% and 68% of workplace air quality safety standards (which range from 25 to 50 micrograms per cubic meter of air).
Critics point out that: (1) the workplace safety standards are based on allowable maximums in the workplace, not mercury body burden; (2) the workplace safety numbers are not applicable to continuous 24hr exposure, they're limited to a normal work day and 40 hr work-week; and (3) the uptake/absorption numbers are averages and not worst case patients (those most at risk).
A study conducted by measuring the intraoral vapor levels over a 24-hour period in patients with at least nine amalgam restorations showed the average daily dose of inhaled mercury vapor was 1.7 µg (range from 0.4 to 4.4 µg), which is approximately only 3.4% of the threshold limit value of the OSHA maximum allowable environmental level of 50 µg/day in the workplace. The World Health Organization (WHO) notes that exposure can be greatly increased by personal habits such as bruxism and gum-chewing and cites a report which found a 5.3 fold increase in mercury levels after chewing, eating, or toothbrushing. They report that amalgam is estimated to contribute 50% of mercury exposure in adults. In the studies the WHO reviews, daily mercury exposure estimates range from 3 μg/day to 9 μg/day.
A Swedish study of autopsies examined the mercury levels in brains and kidneys and found a strong correlation with the number of amalgam fillings. A German study found that mercury urinary excretion was significantly higher in those with dental amalgam fillings.
The NIDR Amalgam Study performed on a cohort of an adult military population of 1127 healthy males found that, based on their cross-sectional data it is estimated that, on average, each ten-surface increase in amalgam exposure is associated with an increase of 1 ug/L mercury in urine concentration.
Research on monkeys has shown that mercury released from dental amalgam restorations is absorbed and accumulates in various organs such as the kidney, brain, lung, liver, gastro-intestinal tract, the exocrine glands. It was also found to have crossed the placental barrier in pregnant rats and shown to cross the gastrointestinal mucosa when amalgam particles are swallowed after amalgam insertion or after removal of old amalgam fillings.
Read more about this topic: Dental Amalgam Controversy