In advanced periodontitis, destruction of the bone and tissue causes deep pockets to form in the space between the gum and teeth, providing a space for bacteria to live and inflict further damage.  The resulting decay often requires the tooth to be permanently removed.  In periodontal pocket reduction surgery, the gum is folded back allowing the removal of the disease-causing bacteria.  In some cases, the tooth surface is smoothed to remove potential places for bacteria to hide.  This allow the gum to attach to healthy bone and reduces the size of any space where bacteria can grow.