Increased mercury emissions from modern dental amalgams

Abstract

All types of dental amalgams contain mercury, which partly is emitted as mercury vapor. All types of dental amalgams corrode after being placed in the oral cavity. Modern high copper amalgams exhibit two new traits of increased instability. Firstly, when subjected to wear/polishing, droplets rich in mercury are formed on the surface, showing that mercury is not being strongly bonded to the base or alloy metals. Secondly, high copper amalgams emit substantially larger amounts of mercury vapor than the low copper amalgams used before the 1970s. High copper amalgams has been developed with focus on mechanical strength and corrosion resistance, but has been sub-optimized in other aspects, resulting in increased instability and higher emission of mercury vapor. This has not been presented to policy makers and scientists. Both low and high copper amalgams undergo a transformation process for several years after placement, resulting in a substantial reduction in mercury content, but there exist no limit for maximum allowed emission of mercury from dental amalgams. These modern high copper amalgams are nowadays totally dominating the European, US and other markets, resulting in significant emissions of mercury, not considered when judging their suitability for dental restoration.

Keywords: Copper amalgam; Mercury; Non-gamma-two; Non-ɣ2.

Fig. 1

Two tablets of copper amalgam in a spoon heated over an open flame ready to be crushed. With courtesy of the Norwegian TV Company NRK

Fig. 2

Droplets of mercury on the surface of modern, high copper non-ɣ2-amalgam, photographed with a light microscope (×252 magnifying). Photo: Ulf Bengtsson

Fig. 3

A sphere of mercury on the surface of modern, high copper non-ɣ2-amalgam, documented with a scanning electron microscope (SEM). Note the strong signal from mercury as the electron beam passes the sphere. Photo: Ulf Bengtsson

Fig. 4

Mercury vapour loss (ng) between 0.5 and 30 min after abrasion. Left group (red cross-hatched bars): non-ɣ2-amalgams; third bar from right (blue hatched): reduced ɣ2-amalgam; right group (two white bars): old, conventional ɣ2–containing amalgams Diagram based on findings in Mahler et al. (1994). (Color figure online)