Dental cleanings involve removing plaque (soft, sticky, bacteria infested film) and tartar (calculus) deposits that have built up on the teeth over time. Your teeth are continually bathed in saliva which contains calcium and other substances which help strengthen and protect the teeth. While this is a good thing, it also means that we tend to get a build-up of calcium deposits on the teeth. This chalky substance will eventually build up over time, like limescale in a pipe or kettle. Usually it is tooth coloured and can easily be mistaken as part of the teeth, but it also can vary from brown to black in colour.