A routine cleaning is called for when a patient has healthy gums or gingivitis. (Gingivitis is reversible changes in the gums and jaw bone. Periodontitis is when there are irreversible changes.) The focus in a routine cleaning is to remove plaque and tartar accumulations on and in between the teeth, at or above the gum line. It is recommended to get a cleaning every six months, and the process takes one visit in most circumstances.
A deep cleaning is needed where there is active gum disease present. In a deep cleaning, the focus on doing everything that is done in a routine cleaning, plus removing the tartar below the gum line. It is this tartar that is causing the inflammation in the gums, which in turn causes the loss of bone that holds the teeth in, as shown in the picture aside.