When tooth is extracted, blood clot usually develops to protect tissue and promote healing. Among other things, this blood clot will create a protective layer to shield bone and nerve endings until the wound has an opportunity to heal. Blood clots create foundation for the growth of new bone and the development of fresh soft tissue.
So as to say, dry socket happens when this blood clot either fails to develop, dissolves or will dislodge before the wound has any chance to heal. Without this protective layer, bone and nerves are left exposed, leading to intense pain inside the tooth socket and along the side of face.
People who usually smoke, have poor oral care, use birth control pills, had third molar extraction or have a history of dry socket, rinse and spit a lot after tooth extraction, drink through straw immediately after extraction are at greater risk of suffering from dry socket.
To treat it your dentist will clean the socket, place a medicated dressing to promote its healing. Furthermore, you might have multiple visits to the dental office to change the dressing until the socket heals.