Open wide...as long as you know which kind of material you want to fill your cavities.

RODALE NEWS, EMMAUS, PA—Developing a cavity is bad enough. But choosing which material to fill it with can be daunting, too. The two major options, amalgam and composite fillings, have both been accused of being potential health threats. So which one should you carry around in your mouth?

This: Amalgam

Pros: Amalgam fillings are much cheaper and last longer than composites—in some cases 50 to 100 percent longer, says Rodway Mackert, D.D.S, professor of oral rehabilitation in the School of Dentistry at the Medical College of Georgia, and Ph.D. in materials science. And despite the presence of mercury, a toxic metal, in amalgam fillings, most people will be exposed only to very low levels of it (0.08 to 0.2 micrograms of vapor per day per filling). Dr. Mackert also points to studies showing that dentists, who can be exposed to mercury for as many as 8 hours per day over a period of 20 to 30 years, don’t build up dangerous levels of mercury in their systems despite their chronic exposure.

Cons: Mercury exposure at any level is concerning, especially for pregnant women and children. Even though the levels of mercury vapors coming from dental fillings aren’t nearly as high as what you’re exposed to by polluted air from coal-fired power plants, eating contaminated fish, and other ambient sources, it’s exposure nonetheless. And mercury fillings continue to release vapors for as long as they’re in your mouth. Disposal is also an issue: Some states and city governments require dentists to install amalgam separators, which prevent 95 to 99 percent of amalgam particles from entering water supplies, but these devices aren’t required everywhere. So it’s possible excess mercury from your procedure could end up in the environment.

That: Composite

Pros: Despite reports to the contrary, Dr. Mackert says that very few composite fillings contain the chemical bisphenol A (BPA), which has been linked to cancer, diabetes, and hormone disruption. Patients are more likely to be exposed to the chemical through dental sealants rather than fillings. And Congress has proposed a ban on BPA, which may eliminate the issue altogether.

Cons: Composite fillings are more expensive and less durable than amalgam. In addition, a few brands do contain BPA, as a primary component or as a product of other materials when they break down.