Allergic dentition is the symptom of abnormal soreness and tenderness of the teeth when exposed to external stimuli such as temperature (cold, heat), chemicals (acid, sweet) and mechanical action (friction or biting hard objects), also known as dentin hypersensitivity. It is not an independent disease, but a common symptom of many dental diseases. The main symptom is that the sensitive area or sensitive teeth produce obvious soreness to cold, hot, sour, sweet and hard object stimuli, and the symptoms disappear immediately after the stimuli are removed. In severe cases, the patient is afraid to bite and chew, or even to breathe through the mouth, but there is no spontaneous pain. The principle of dentin hypersensitivity treatment is to close the dentin tubules and isolate them from external stimuli. Depending on the loss of hard tissue and the degree of the disease, the appropriate treatment is chosen. In most cases, conservative treatment methods are used as much as possible. For mild defects, fluoride, strontium chloride, and silver iodide are used for drug desensitization. For deeper defects, glass ionomer or composite resin filling repair is the best treatment available. Severe defects with poor filling results can be restored with artificial crowns; while individual defects near the tooth flap. For those with obvious clinical symptoms, endodontic treatment can be considered. 1.Why is the tooth allergic? Under normal circumstances, teeth can tolerate temperature changes in the range of 20-50 ℃, therefore, drinking cold drinks and eating hot pot will not cause tooth allergy and soreness. This is due to the fact that the surface of healthy teeth is a layer of intact hard enamel and the inner layer of dentin is rich in nerve endings, which can be insulated from external stimuli under the enamel coating. However, if the integrity of the enamel is destroyed due to some reasons, such as wear, wedge-shaped defects, caries or atrophy, the dentin is exposed and the nerve endings are exposed, and when exposed to foods that are too cold, too hot or sweet and sour, allergic symptoms may occur. In addition, some neurosis patients, menstruating, expectant women, or long-term insomnia, may be due to high systemic stress, the sensitivity of nerve endings increased, will also appear dental sensitivity symptoms, such patients usually with the general condition of the improvement of sensitivity symptoms naturally disappear. 2, what is the performance of tooth wear? Wear refers to the slow loss of hard tissue caused by mechanical friction between teeth or between teeth and foreign objects. Under normal quiet conditions, chewing will cause a certain degree of hard tissue loss, eruption of more than 10 years of permanent teeth on the occlusal surface or cusp of the incisive edge will be found in varying degrees of wear, which is a normal physiological phenomenon, which is beneficial to maintain the balance of chewing. Chewing-induced wear (also known as abrasion) initially appears as a small circular or oval plane on the cusp or incisal edge, smooth and flat, and then gradually increases and deepens, yellow dentin is exposed, and in heavy cases, the cusp is ground flat, some elderly teeth have almost complete loss of enamel at the tread and incisal edge, high dentin wear, shortened crowns, and even crista-like structures. Since teeth have certain ability to repair themselves, worn teeth do not necessarily have symptoms, but if the wear rate is faster due to frequent chewing of hard food, night grinding and other habits, and it is too late to repair, dentin allergy symptoms may appear, which is the main reason why most patients with worn teeth come to the clinic. In addition to the destruction of the appearance of worn teeth, the original occlusion and adjacent relationship also changed, bringing a series of problems such as food embedment, disruption of the occlusal relationship, damage to the jaw joint, etc., affecting the periodontal tissue and the oral cavity. If the bad habits are not treated or corrected in time, the dentin will be worn out and the tooth will be exposed, which will cause pulp or apical inflammation. The wear and tear caused by bad habits such as card melon, biting the pencil is mostly manifested as a certain tooth incisal edge defect, which generally only shows the loss of enamel and affects the beauty. 3.What’s the matter with the notch in the neck of the tooth? Many patients go to the doctor because of tooth allergy, after examination found that the neck of the allergic tooth some time appeared grooves, these grooves consist of two pinched surface, in the form of large mouth bottom small wedge-shaped or ” V ” shaped defect, the two walls of the groove surface hard, smooth, no staining. The surface of both walls of the groove is hard and smooth, without staining. It resembles the wedge commonly used in wood furniture making, and is clinically known as “wedge-shaped defect”. Because of the destruction of the enamel in the defect, the dentin is exposed and therefore the symptoms of dentin hypersensitivity appear. In the early stages, the defect is shallow, linear and asymptomatic. In severe cases, the defect can penetrate the pulp cavity and cause the corresponding symptoms of odontitis and periapical inflammation, and even lead to tooth fracture. How does a wedge-shaped defect form? Improper brushing is the main reason. In order to be able to thoroughly clean teeth, many people brush teeth with force across the brush, not knowing that the drip can penetrate the stone, coupled with the relative weakness of the tooth neck structure, poor wear resistance, and is the chewing lifting force concentration, the month. Long-term immersion in the gingival sulcus fluid that can promote tissue demineralization, the combined effect of internal and external factors, the hard tooth hard tissue may appear defective. In addition, some studies have found that coarser particles of dental bruises, hardness of toothbrush bristles, and habitual consumption of acidic beverages are associated with defect formation. Shallow defects with no symptoms may be left untreated. Or desensitization treatment can be done as needed. Deeper defects should be filled and restored. The key to preventing defect formation is to adopt a proper brushing style and avoid “sawing” horizontal brushing. Irrespective of the presence or absence of the disease and its degree, any improper brushing should be corrected immediately.