In 1987, Sikorski et al studied 81 female dentists and dental assistants in Poland and compared them to 34 controls without occupational exposure to mercury . These investigators found a direct relationship between total mercury levels in hair and the incidence of reproductive failures and menstrual cycle disorders, including children born with birth defects . Although it is sometimes cited as evidence of the occupational dangers of amalgam (and by extension of the dangers of amalgam fillings), Larsson detailed several problems with the study . The hair samples were obtained from 3 to 18 years after the birth of the children with birth defects, rendering the study irrelevant to mercury levels during pregnancy. Hair samples are usually a poor indicator of mercury vapor exposure anyway. Although the study population lived in a country with high levels of industrial pollution, other possible sources of mercury were not reported. The authors did not report how they randomly chose the control group. Five of the infants born to the study group had spina bifida, whose etiology is unknown.
In a much larger study in 1989, Ericson and Källén studied 8157 infants in Sweden born to dentists, dental assistants, or dental technicians and found no increased risk for spina bifida, perinatal survival, low birthweight, or malformations compared to all births. The only difference between the infants of dental workers and the infants of the rest of the population was that the infants of the dental workers actually had a lower perinatal death rate. In other investigations, these authors also found no greater risk of spontaneous abortions in dental workers and concluded that there is no increased reproductive risk in the dental occupations in Sweden .
Brodsky et al surveyed 21,634 male dentist and 21,202 dental assistant respondents. High exposure was defined as 40 or more amalgam restorations per week; low exposure was defined as fewer than 40 amalgam restorations per week. After dividing respondents into high and low exposure groups, the investigators found no difference in the rate of spontaneous abortions or congenital abnormalities of offspring between the low and high exposure groups, either between dental assistants or the wives of dentists .
Rowland et al reported that women dental assistants with relatively high occupational exposure to mercury vapour were less fertile than unexposed women controls . But women with low exposure were actually more fertile than the unexposed controls. The study is of limited relevance, however, as mercury vapor levels were not determined, and the study did not include women who did not conceive or unmarried women who were trying to get pregnant. Fertility was determined in women who had been pregnant by the women's recollection of the number of menstrual cycles until pregnancy while having unprotected sexual intercourse so it is possible the women would have to recollect events well over five years in the past. In a 1994 study of 859 female dentists and 755 female teachers, fertility did not differ between the two groups . A similar study in 1999 reached the same conclusion .
Heidam compared the risk of spontaneous abortions among groups of females occupationally exposed to chemicals including dental assistants, factory workers, gardening workers, and painters to a reference group of less exposed employees including physiotherapists, occupational therapists, office workers, and technical assistants and designers. There were no differences in the rate of spontaneous abortions between the dental assistants and the reference group although the factory workers and painters had a significantly higher rate of spontaneous abortions than did the reference group .
Warfvinge reported a case of a 30-year-old female dentist exposed to very high levels of mercury from a leaking amalgamator for about one year . Mercury vapor levels in the air were as high as 840 µg/m3 and urinary mercury levels were as high as 60 µg Hg/l. The amalgamator was repaired, and about a year later, the dentist became pregnant. She gave birth to a normal weight baby who appeared clinically healthy at 2 years old when the article was published.
Mercury from dental amalgams (inorganic mercury) is probably not as harmful to the fetus as organic mercury and mercury salts. There does not seem to be a risk of spontaneous abortion  or neurologic defects . In an extensive review the literature in 1999, Schuurs concluded that "negative reproductive effects from exposure to mercury in the dental office are unproven, but safe levels have not been established.in view of the in general low amounts of mercury stemming from dental amalgam fillings, the population at large is at even less risk than dental staff." 
Dr. Wahl practices dentistry in Wilmington, Delaware. This article was originally published in Quintessence International 32:696-710, 2001, and is reproduced here with the kind permission permission of Quintessence Publishing Co. The author thanks Drs. J. Rodway Mackert, Ivar A. Mjör, and Fred Eichmiller for reading the manuscript and offering several helpful suggestions.