The relationship between amalgam restorations and mercury levels in male dentists and nondental health professionals.
OBJECTIVE
The objectives of this study were: (1) to compare the mercury levels in general dentists with the mercury levels in other health professionals using toenail clippings as a biomarker, (2) to identify risk factors associated with high mercury levels, and (3) to compare practice characteristics of dentists with high and low mercury levels.


METHODS
A sample of 579 men was randomly selected from the 33,737 men participating in the Health Professionals Follow-up Study who had provided toenail samples in 1987. A questionnaire was sent to these male subjects in 1991 to obtain information on fish consumption, toothbrushing frequency, number of teeth, number of amalgam restorations, general practice or specialty status, number of amalgam restorations placed and removed per week, mercury storage and handling procedures, and mercury spillage incidents. A measure of long-term mercury exposure was obtained from toenail samples using neutron activation analysis for the 410 respondents (71% response rate). The 90th percentile mercury level in toenails (0.88 ppm) was selected as the threshold for elevated toenail mercury level.


RESULTS
No relationship was found between the number of dental amalgams and toenail mercury levels among general dentists, dental specialists, and nondental health professionals. General dentists were found to have more than twice the level of mercury in toenails than nondental health professionals (mean level = 0.94 vs 0.45) and 60 percent higher than dental specialists (mean = 0.59). The combined use of disposable capsules and water storage of scrap amalgam appeared to reduce the risk of elevated mercury levels. Regardless of professional status, consumption of tuna and saltwater fish were the primary exposure factors that were positively associated with toenail mercury levels.


CONCLUSIONS
As shown by the associations with dental profession and fish consumption, the mercury content of toenails is a stable biomarker of cumulative long-term mercury exposure. The lack of association between nail mercury levels and number of amalgam restorations suggests that avoidance of mercury amalgam restorative materials cannot be justified by the presence of mercury released from dental amalgams.
Joshi
Anil
A
Harvard School of Dental Medicine, Boston, MA 02115, USA.
Douglass
Chester W
CW
Kim
Hyun-Duck
HD
Joshipura
Kaumudi J
KJ
Park
M Chu
MC
Rimm
Eric B
EB
Carino
Michael J
MJ
Garcia
Raul I
RI
Morris
J S
JS
Willett
Walter C
WC
D000818:Animals; D001822:Body Burden; D003723:Dental Amalgam; D003793:Dental Restoration, Permanent / Q000706:statistics & numerical data; D003815:Dentists / Q000706:statistics & numerical data; D004032:Diet; D005399:Fishes; D006282:Health Personnel / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D008628:Mercury / Q000032:analysis*; D008875:Middle Aged; D009262:Nails / Q000737:chemistry*; D016273:Occupational Exposure; D012044:Regression Analysis; D014413:Tuna
D003723:Dental Amalgam; D008628:Mercury