Occult fractures, also known as incomplete fractures or microfractures, are small, non-physiological cracks on the surface of the tooth crown. Occult fissures are more common in clinical practice, but because the cracks are not obvious and easy to be overlooked, the clinical manifestations are different and can easily lead to omission or misdiagnosis, resulting in delayed treatment, which eventually leads to the destruction of tooth structure and loss of masticatory function, and even causes tooth fracture and loss of retention, therefore, occult fissures have become the third major factor causing missing teeth after caries and periodontal disease. Etiology of tooth occlusion 1, the weak link of tooth structure is the susceptibility factor of occluded tooth fracture, such as developmental groove, the sulcus and enamel plate in the tooth structure of normal people is the defective area left by tooth development, not only the crack resistance strength itself is low, but also the part where the stress is concentrated when the tooth is subjected to normal dental force, so it is easy to occur occluded fracture, which is the intrinsic factor of occluded tooth fracture. 2, excessive wear, too steep cusps, etc. makes the cusp slope increase, the greater the cusp slope, the horizontal force generated also increases, also prone to occlusion crack. 3, traumatic (dental) force is the fracture-causing factor of the occult fracture occult fracture, due to excessive wear of the tooth tip and uneven occlusion, the greater the traumatic (dental) force generated, the greater the chance of occult fracture. 4, dietary habits: people who like to eat nuts, coarse fiber food, dried meat and other foods are more likely to occur dental fissure than others, the reason may be: on the one hand, when the teeth suddenly contact the hard objects in the food, resulting in unexpected traumatic dental force, in the weak susceptible area of the tooth to produce stress concentration, resulting in the occurrence of fissure. On the other hand, the habit of chewing hard objects for a long time tends to accelerate and aggravate the degree of pathological wear and tear, forming high steep tooth cusps. 5, age factor: Mostly seen in the middle-aged and elderly population, dental occult fracture is mostly chronic progressive injury, and as age increases, the fissure also gradually aggravates, eventually leading to fracture of the tooth body. In addition, with age, the inorganic components in the tooth structure increase, the bonding effect between the enamel columns decreases, the cellular tissue in the pulp vessels decreases, and the nutrient effect of supplying the tooth body decreases. These factors increase the brittleness of the dentition, which in turn leads to the occurrence of occult fractures. Diagnosis of occult fissure 1. History and symptoms: chronic chewing discomfort and sharp chewing pain at fixed points. 2.Visual diagnosis: Typical cracks are colored by staining with food or drink and can be diagnosed by direct observation. Because the doctor is limited by the minimum distance and contrast conditions that the naked eye can see, small cracks are not easily detected. 3.Percussion: discomfort on percussion and obvious response to lateral percussion can help locate the affected tooth. 4.Temperature test: When the pulp vitality temperature test is performed, sudden and obvious temperature changes can induce a certain degree of reaction or pain in the pulp, among which the reaction at the crack is obvious. 5.Staining method: Generally, 2% tincture of iodine or 1% methyl violet solution is used to coat the suspected cryptoclastic area, and then 75% alcohol cotton balls are used to dry the staining solution. Since alcohol can only wipe away the dye on the surface of the affected tooth, the color of the dye inside the cryptoclastic line is still present and becomes more obvious, which is diagnostic. 6.Transillumination method: The light source of the optical fiber illuminator is used to illuminate the tooth under test, and when the light is at a certain angle with the tooth folds, the tooth folds on the side near the light source will be bright, while the part far from the light source will be dark. 7.Bite diagnosis: Place a small cotton ball or a small wooden stick on the suspected occluded fracture and ask the patient to bite down, if the tooth has an occluded fracture, it can produce pain. 8.Dental microscope: The width of the occluded fissure is usually less than 18 microns, and the microscope can effectively see the occluded fissure when magnified 16 times. 9.X-ray auxiliary examination: Cryptoclastic teeth can sometimes see a widening of the periodontium gap in a certain area, a widening of the corresponding sclerotic plate or a translucent area in the alveolar bone. Treatment of occluded tooth 1.Causal treatment: adjusting (dentition) to reduce (dentition) interference; reducing the cusp slope to reduce the splitting force and equalize the occlusal force burden of the whole mouth; treating or extracting other affected teeth in the whole mouth and repairing missing teeth. 2, symptomatic treatment (1) shallow occult crack, no endodontic symptoms, composite resin filling treatment. (2) For deeper cryptocracks with pulpal symptoms, adjust the cusp slope at the same time of pulpal treatment, and restore the full crown in time after the root canal treatment is completed, and try to shorten the treatment period to prevent the crown from splitting during the root canal treatment. (3) If the affected tooth splits due to occult fracture, treatment such as crown lengthening or extraction of the affected tooth should be done according to the position of the tooth and the location of the split. Since the clinical symptoms and manifestations of cryptic fracture vary with the degree of the tooth, and the prognosis of the tooth becomes worse with the expansion of the fracture, early diagnosis, early prevention and early treatment are crucial.