Tooth scaling removes plaque and hard crusty calculus deposits, also known as tartar. Both of which are loaded with bacteria.
Sub-gingival tooth scaling is necessary when plaque and tartar are detected below the gum line.
Sometimes after a tooth scaling, the roots of a tooth must be planed in order to create a smooth surface for the gum tissue to re-attach to. In addition to the planing, your dentist may also prescribe medication in order to control infection and pain.