Why you need them:
Plaque - a sticky, almost colorless layer of bacteria that forms on your teeth - mixes with the sugars in food to produce decay-causing acids. When decay creates a cavity, the dentist usually fills it with a durable material, most often a composite (a tooth colored material), a metal alloy called amalgam, or gold. It typically only takes one visit to complete this procedure, and a filling usually lasts an average of 5 years, depending on its location, the material used, and the care you give your teeth. Gold has the longest lifespan, followed by amalgams and then composites.
At the site of the decay the dentists cleans out the decay and shapes the tooth to hold the filling.
The hole is filled with the appropriate material for the cavity's size and location (a composite and an amalgam filling are shown.).