tissue which consists of proliferating fibroblasts and endothelial cells derived from remnants of the periodontal membrane, surrounding alveolar bone and gingival mucosa. In time this in turn is replaced by coarse, fibrillar bone and finally by mature, woven bone. The clot may fail to form because of poor blood supply (e.g., secondary to local factors such as smoking, anatomical site, bone density and conditions which cause sclerotic bone to form). The clot may be lost because of excessive mouth rinsing, or disintegrate prematurely due to fibrinolysis. Fibrinolysis is the degeneration of the clot and may be caused by the conversion of plasminogen to plasmin and formation of kinins. Factors which promote fibrinolysis include local trauma, estrogens, and pyrogens from bacteria. Bacteria may secondarily colonize the socket, and lead to further dissolution of the clot. Bacterial breakdown and fibrinolysis are widely accepted as major contributing factors to the loss of the clot. Bone tissue is exposed to the oral environment, and a localized inflammatory reaction takes place in the adjacent marrow spaces. This localizes the inflammation to the walls of the socket, which become necrotic. The necrotic bone in the socket walls is slowly separated by osteoclasts and fragmentary sequestra may form. The bones of the jaws seem to have some evolutionary resistance to this process. When bone is exposed at other sites in the human body, this is a much more serious condition. In a dry socket, healing is delayed because tissue must grow from the surrounding gingival mucosa, which takes longer than the normal organisation of a blood clot. Some patients may develop short term halitosis, which is the result of food debris stagnating in the socket and the subsequent action of halitogenic bacteria. The main factors involved in the development of dry socket are discussed below. Extraction site Dry sockets more commonly occur in the mandible (lower jaw) than the maxilla (upper), due to the relatively poor blood supply of the mandible and also because food debris tends to gather in lower sockets more readily than upper ones. It more commonly occurs in posterior sockets (molar teeth) than anterior sockets (premolars and incisors), possibly because the size of the created surgical defect is relatively larger, and because the blood supply is relatively poorer at these sites. Dry socket is especially associated with extraction of lower wisdom teeth. Inadequate irrigation (washing) of the socket has been associated with increased