When bacteria destroy the tissue around the tooth- root, an empty space appears which we call a periodontal pocket.
Periodontal pocket has a tendency to grow, i.e. to progress to the top of the tooth root. Due to the fact that the connective tissue more and more destroys, at some point it happens that nothing holds the tooth in a dental cup. It results first in teeth oscillation, and then, after some period of time, we are faced with tooth-loss.
When periodontal pocket is deeper than 4mm, it is necessary to perform flap surgery, if possible. In terminal stage the tooth-loss is inevitable.