accumulate beneath the operculum, which is an area that is difficult to keep clean because it is hidden and far back in the mouth. the opposing upper wisdom tooth also tends to have sharp cusps and over-erupt because it has no opposing tooth to bite into, and instead traumatizes the operculum further. periodontitis and dental caries may develop on either the third or second molars, and chronic inflammation develops in the soft tissues. chronic pericoronitis may not cause any pain, but an acute pericoronitis episode is often associated with pericoronal abscess formation. typical signs and symptoms of a pericoronal abscess include severe, throbbing pain, which may radiate to adjacent areas in the head and neck,: 122 redness, swelling and tenderness of the gum over the tooth.: 220–222 there may be trismus (difficulty opening the mouth),: 220–222 facial swelling, and rubor (flushing) of the cheek that overlies the angle of the jaw.: 122 persons typically develop pericoronitis in their late teens and early 20s,: 6 as this is the age that the wisdom teeth are erupting. treatment for acute conditions includes cleaning the area under the operculum with an antiseptic solution, painkillers, and antibiotics if indicated. after the acute episode has been controlled, the definitive treatment is usually by tooth extraction or, less commonly, the soft tissue is removed (operculectomy). if the tooth is kept, good oral hygiene is required to keep the area free of debris to prevent recurrence of the infection.: 440–441 occlusal trauma occlusal trauma results from excessive biting forces exerted on teeth, which overloads the periodontal ligament, causing periodontal pain and a reversible increase in tooth mobility. occlusal trauma may occur with bruxism, the parafunctional (abnormal) clenching and grinding of teeth during sleep or while awake. over time, there may be attrition (tooth wear), which may also cause dentin hypersensitivity, and possibly formation of a periodontal abscess, as the occlusal trauma causes adaptive changes in the alveolar bone.: 153–154 occlusal trauma often occurs when a newly placed dental restoration is built too "high", concentrating the biting forces on one tooth. height differences measuring less than a millimeter can cause pain. dentists, therefore, routinely check that any new restoration is in harmony with the bite and forces are distributed correctly over many teeth using articulating paper. if the high spot is quickly eliminated, the pain disappears and there is no permanent harm.: 153, 753 over-tightening of braces can cause periodontal pain and, occasionally, a periodontal abscess.: 503 alveolar osteitis alveolar osteitis is a complication of tooth extraction (especially lower wisdom teeth) in which the blood clot is not formed or is lost, leaving the socket where the tooth used to be empty, and bare bone is exposed to the mouth. the pain is moderate to severe, and dull, aching, and throbbing in character. the pain is localized to the socket, and may radiate. it normally starts two to four days after the extraction, and may last 10–40 days.: 122 : 216–217 healing is delayed, and it is treated with local anesthetic dressings, which are typically required for five to seven days.: 216–217 there is some evidence that chlorhexidine mouthwash used prior to extractions prevents alveolar osteitis. dental trauma and cracked tooth syndrome crown-root fracture with pulp involvement (left). extracted (right). cracked tooth syndrome refers to a highly variable set of pain-sensitivity symptoms that may accompany a tooth fracture, usually sporadic, sharp pain that occurs during biting or with release of biting pressure, or relieved by releasing pressure on the tooth.: 24 the term is falling into disfavor and has given way to the more generalized description of fractures and cracks of the tooth, which allows for the wide variations in signs, symptoms, and prognosis for traumatized teeth. a fracture of a tooth can involve the enamel, dentin, and/or pulp, and can be orientated horizontally or vertically.: 24–25 fractured or cracked teeth can cause pain via several mechanisms, including dentin hypersensitivity, pulpitis (reversible or irreversible), or periodontal pain. accordingly, there is no single test or combination of symptoms that accurately diagnose a fracture or crack, although when pain can be stimulated by causing separation of the cusps of the tooth, it's highly suggestive of the disorder.: 27–31 vertical fractures can be very difficult to identify because the crack can rarely be probed: 27 or seen on radiographs, as the fracture runs in the plane of conventional films (similar to how the split between two adjacent panes of glass is invisible when facing them).: 28–9 when toothache results from dental trauma (regardless of the exact pulpal or periodontal diagnosis), the treatment and prognosis is dependent on the extent of damage to the tooth, the stage of development of the tooth, the degree of displacement or, when the tooth is avulsed, the time out of the socket and the starting health of the tooth and bone. because of the high variation in treatment and prognosis, dentists often use trauma guides to help determine prognosis and direct treatment decisions. the prognosis for a cracked tooth varies with the extent of the fracture. those cracks that are irritating the pulp but do not extend through the pulp chamber can be amenable to stabilizing dental restorations such as a crown or composite resin. should the fracture extend though the pulp chamber and into the root, the prognosis of the tooth is hopeless.: 25 periodontic-endodontic lesion apical abscesses can spread to involve periodontal pockets around a tooth, and periodontal pockets cause eventual pulp necrosis via accessory canals or the apical foramen at the bottom of the tooth. such lesions are termed periodontic-endodontic lesions, and they may be acutely painful, sharing similar signs and symptoms with a periodontal abscess, or they may cause mild pain or no pain at all if they are chronic and free-draining. successful root canal therapy is required before periodontal treatment is attempted.: 49 generally, the long-term prognosis of perio-endo lesions is poor. non-dental discomfort caused by coronary artery disease can radiate to the neck, lower jaw and teeth