Which form of mercury poses the principal occupational hazard in the dental surgery, and which form is the most toxic overall?

Correct answer: C. Elemental mercury vapour is the occupational hazard; methylmercury is the most toxic form

• A. Ethylmercury (thiomersal) is a preservative in some vaccines, not a dental occupational hazard.
• B. Inorganic salts are corrosive on ingestion but are not the principal dental exposure route.
• C. CORRECT. In the dental setting the exposure is to ELEMENTAL mercury as VAPOUR — released when amalgam is triturated, condensed, polished or removed, and from any spillage. Inhaled vapour crosses the alveolar membrane and the blood-brain barrier readily and targets the central nervous system and kidneys. However, the most toxic form of mercury in general is the ORGANIC form, METHYLMERCURY, which bioaccumulates in the food chain and is the agent of Minamata disease — but it is not encountered in dentistry.
• D. This reverses the two: methylmercury is not an occupational dental exposure.

Note: Hygiene measures: work in a well-ventilated surgery, use pre-capsulated alloy, use water spray and high-volume suction when removing old amalgam, store scrap under sulphide solution, and never handle amalgam with bare hands or use an ultrasonic condenser.