We need teeth cleanings for two reasons:
Teeth cleanings remove the buildup of plaque and tartar. This buildup is for the most part natural — kind of like how a boat picks up barnacles just by being in the ocean. But too much buildup leads to gum disease.
The reason tartar needs to be removed is because your body sees it as a foreign invader. As with any other foreign invader, like a flu bug or an infection, your body “sends in the troops” using the immune system to fight off the infection. There is a battle in your mouth at all times, and the war is never over. Teeth cleanings level the playing field by keeping things in check.