1.Caries (qu) teeth . Caries, commonly known as worm teeth, is a kind of gradual destruction (defect) disease that occurs in the crown part of the teeth or in the root part of the teeth after the gum recession of the elderly under the influence of many factors mainly by bacteria. Caries is often divided into three stages: superficial caries, medium caries and deep caries. Superficial caries: it is often located in the most surface layer of the crown, and also seen in the exposed surface of the root of the old people (dental bone). It shows that the color of the affected part is yellowish-brown or black, and the surface is rough; there is no uncomfortable symptom at this stage. Middle caries: The damage has progressed to the superficial layer of the second layer of the crown (dentin), which shows that the cavity has been formed in the part of the crown or the part of the root. At this stage, there is usually painful sensation to cold, hot, sour and sweet stimulation. Deep caries: The damage progresses to the deep layer of the second layer (dentin) of the tooth, which shows that there is already a very obvious deep cavity. At this stage, it usually produces more intense instant pain to cold, hot, sour and sweet stimulation. 2.Acute tooth damage. That is, the damage involves the crown or root part of the tooth and the surrounding tissues under the action of external force. (1) Tooth shock refers to the tooth under the action of external forces, to the fixed root and a thin layer of fibrous tissue (periodontal membrane) in the alveolar bone of mild damage, the crown of the tooth root are intact. The manifestation is: after the injury, the affected tooth has the discomfort of elongation, there is a relatively slight loosening, there may be pain on percussion, and some patients may also be accompanied by a small amount of bleeding from the gingival margin. (2) Tooth dislocation refers to the tooth being dislodged from the alveolar socket (alveolar bone) under the action of external force. Tooth dislocation can be divided into incomplete dislocation and complete dislocation. Incomplete dislocation: The tooth damaged by external force leaves its original position and deviates from the alveolar socket (shifts to the left, right, up or down), but does not leave the mouth. Total dislocation: The tooth is completely dislocated from its original position, leaving the alveolar bone and gums, and leaving the mouth. (3) Crown and root fracture: the fracture of the crown and root part of the tooth under the action of external force. 3.Wedge-shaped defect. It is a kind of defect caused by slow depletion of the part of the crown near the gingival end (cervical part of the tooth), named because the kind of defect is often triangular wedge-shaped. The main reason for consumption: brushing teeth with force across the brush; also because this part of the tooth is the crown and root bonding site, its special structure is weaker, easy to be worn away; some patients own acidic exudate in the gum is also related to the defect, followed by biting this part is the main bite force bearing area of the teeth (stress concentration area), tooth tissue can be due to long-term bearing fatigue and defect. 4.Dentin hypersensitivity. It is often caused by the rapid exposure of dentin due to caries, abrasion, crown fracture, wedge-shaped defect, gum atrophy, etc., or the increased sensitivity of peripheral nerve during menstruation and pregnancy of women, resulting in tooth pain caused by cold, hot, sour, sweet, friction and biting hard objects. 5.Acute pulpitis. It refers to the pulp inflammation caused by acute physical damage, chemical stimulation and infection, such as excessive heat production caused by surgical cutting of dental tissues, and chemical stimulation of filling materials. and dental caries, caries leading to pulp inflammation is the most common etiology. The clinical symptoms are mainly spontaneous (sudden appearance of symptoms without any external stimulation) severe pain, and the location of the pain cannot be clearly localized, the pain is radioactive to the ipsilateral head and face are painful, the pain is aggravated for a while and relieved for a while, the pain is more intense at night than during the day, affecting sleep, the stimulation of temperature (cold or hot water) will aggravate the pain. 6. Chronic pulpitis. The causative factors are the same as those of acute pulpitis. Clinical symptoms Chronic pulpitis generally does not occur severe spontaneous pain, but sometimes there can be inconspicuous bouts of hidden pain; because the course of chronic pulpitis is generally long, all patients can be accompanied by a long period of cold, hot stimulation pain process; there can be mild pain when biting, or there is food embedded in the cavity will cause more obvious pain; pain affected teeth can mostly be clearly localized. 7.Periapical periodontitis. Periapical periodontitis refers to the inflammatory disease that occurs in the tissue around the apical part of the tooth root, mostly caused by pulpitis without timely and perfect treatment of the inflammation continues to progress. Periapical periodontitis can have both acute and chronic inflammatory manifestations. The clinical symptoms of acute periapical periodontitis are mainly persistent (symptoms persist without self-remission) severe pain, the location of the painful tooth can be fully defined, the affected tooth has a sense of elongation (growth), when biting the tooth will first touch the painful tooth, biting or touching will increase the pain, the affected tooth is accompanied by mild loosening, temperature (hot and cold) stimulation of the affected tooth does not respond. The clinical symptoms of chronic periapical periodontitis are generally painless, but some patients may experience discomfort in the affected tooth when chewing (self-conscious tooth weakness or slight pain), and the longer duration of the disease may be accompanied by the appearance of small abscesses on the upper end of the gum corresponding to the affected tooth, which may repeatedly bleed or swell. Because chronic periapical periodontitis has a long course, the long-term damage to the apical part of the root caused by inflammation can lead to resorption of alveolar bone or changes in bone density in the apical part of the tooth, and this pathology must be clarified by taking dental radiographs, which is the most important basis for the doctor to make a definitive diagnosis.