Peroxide, when exposed to amalgam fillings, triggers the release of small amounts of mercury the fillings contain. Whether this poses a significant health risk is being hotly debated.
Dental Use of Mercury
Half of an amalgam filling consists of mercury. Exposure to high levels of mercury is toxic, and pregnant women, babies, and young children, in particular, are medically advised to avoid exposure to prevent memory impairment and other serious conditions. As a result, the use of mercury in dental fillings has become controversial. Today, most fillings are made of synthetic materials (composite), but about 30 percent are still amalgam because their “strength and durability...make them useful for...fillings in the back teeth where chewing forces are greatest,” the American Dental Association says.
Dental Use of Peroxide
Hydrogen peroxide and carbamide peroxide are chemicals used as teeth whiteners. Diluted amounts are also used in toothpastes and mouth rinses to disinfect teeth and prevent plaque build-up and gum inflammation.
Peroxide is corrosive, and “mercury ions are released from dental amalgam when bleached,” researchers at the University of Manchester’s School of Dentistry reported. After exposing amalgam to peroxide-based bleaching agents, they reported “significant increases in mercury ion release.”
The Food and Drug Administration has acknowledged that dental amalgam fillings release mercury (mostly as vapor) but, in its final regulation regarding their use, said that “the levels released...are not high enough to cause harm in patients,” including pregnant women and children.
The European Union's Scientific Committee on Consumer Products advice is at odds with the FDA's. The committee referred to laboratory studies that found mercury release from dental amalgams exposed to carbamide peroxide solutions was up to 30 times higher than from those dipped in saline. The committee advised that although the “clinical significance...is unclear,” using peroxide on amalgam-filled teeth “should be approached with caution.”