Deep teeth cleaning is also known as Scaling and Root Planing. It is very different from a regular cleaning. A regular cleaning focuses on the surfaces of the teeth and between teeth above the gum line. During a regular cleaning, the teeth are also polished.
A deep teeth cleaning, on the other hand, is needed in order to remove bacteria, calculus (tartar), and debris that has collected under the gum line. The presence of calculus under the gum line creates a safe haven for bacteria to collect, and cannot be removed by brushing, flossing or with a regular cleaning.
The presence of this bacteria causes an immune response from the body. This immune response results in inflammation, to fight the bacterial infection. If left untreated, the infection and inflammation will continue and progress further under the gum line, resulting in loose teeth and bone loss, and ultimately, the loss of one or more teeth.