First what is a filling? A filling is a material placed in teeth that help stop the process of decay and/or repair and replace fractured tooth structure.
There are two types of filling materials. One type is silver in color “amalgam” Which has been used for over 100 years and is a combination of different metals, including copper, silver, and mercury. The other type is a tooth colored (composite) resin which is bonded to the tooth and is made up of acrylic plastics, quartz fillers, and colorants.
The advantages to composite fillings are first and foremost they are more esthetically pleasing in appearance and second they are less sensitive to hot and cold.
The advantage to an amalgam filling is that they are more economical and they last a bit longer over time.
Both amalgam and composite restorations break down over time. Amalgam corrodes, expands and contracts to the point of break down around the margins and leakage occurs.
And sometimes the tooth structure fractures. Composites actually dissolve over time, they tend to discolor, and get tiny pits in them. Composites also expand and contract when heated by hot coffees, teas, and soups or cooled with foods such as ice cream. The break down also mostly occurs around the margins where the bonding is compromised and leakage occurs.
Amalgam is still up for debate on its toxicity. But studies have shown that normal grinding and chewing show that 5-6 fillings release about the same amount of mercury as a tuna fish sandwich.