Tooth Colored Fillings Defined!

Tooth-colored fillings that are designed to match the color of your teeth are called composites. Composites
 are a mixture of glass or quartz filler that provide good durability and resistance to fracture in small- to mid-
size restorations that need to withstand moderate pressure from chewing. They are generally used on either
front or back teeth.
Composites are "bonded" or adhered in a cavity. This can allow your dentist to make a more conservative repair to your tooth, meaning less tooth structure is removed when the dentist prepares the tooth. This may result in a smaller filling than that of a metal (amalgam) filling.
It generally takes longer to place a composite filling than it does for a metal filling. That’s because composite fillings require the tooth be kept clean and dry while the cavity is being filled.
This article taken from: http://www.mouthhealthy.org/en/az-topics/c/composite-fillings.aspx