of;
Public;
Health,;
Key;
Lab;
of;
Public;
Health;
Safety;
of;
the;
Ministry;
of;
Education,;
Fudan;
University,;
Shanghai,;
China;
Stomatological;
Disease;
Center,;
Shanghai,;
China;
of;
Epidemiology;
and;
Community;
Medicine,;
University;
of;
Ottawa,;
Ottawa,;
Canada;
dental; restoration; nickel-chromium; based; alloys; population; investigation; urinary; chromium; urinary; nickel;