Even if you take great care of your teeth, you still have bacteria in your mouth. They mix with proteins and food byproducts to form a sticky film called dental plaque. This gunk coats your teeth, gets under your gum line, and sticks to fillings or other dental work.
When plaque stays on your teeth, it hardens into tartar.
Tartar, also called calculus, forms below and above the gum line. It's rough and porous and can lead to receding gums and gum disease. It must be removed with special tools in the dentist's office.