Wisdom tooth refers to the innermost third molar tooth on alveolar bone in human mouth, which is just the eighth tooth from the central incisor. Because it broke out very late, it usually broke out between 16 and 25 years old. At this time, people's physical and psychological development is close to maturity, which symbolizes the arrival of wisdom, so it is commonly known as "wisdom teeth". In the growth of wisdom teeth, there are great differences among individuals. Usually there should be four teeth that are symmetrical up and down, some have less than four or none, and very few people will have more than four teeth. The eruption age also varies greatly. Some people break out before the age of 20, while others are in their forties or fifties or have a short life span. This is a normal phenomenon. Wisdom tooth refers to the third molar, which grows in the innermost part of alveolar bone. Most people will sprout wisdom teeth at the age of 16-25. Some wisdom teeth can grow normally and play the role of chewing, but most of them are crooked and grow against adjacent teeth. Some just stop at the head, some don't come out at all, and they grow in various positions in alveolar bone, and many people don't grow at all. Modern medicine generally believes that wisdom teeth are the remnants of human evolution. Because wisdom teeth grow at the end of alveolar bone, the alveolar bone of modern people is degraded in length, width, strength and other aspects due to more and more elaborate diet, which leads to insufficient space for the eruption of wisdom teeth, so that wisdom teeth often erupt out of place and are blocked due to lack of space. In addition, the degradation of wisdom teeth itself will also lead to insufficient eruption and asymmetric eruption. These eruptive abnormalities, as well as the difficulty of cleaning and prevention, usually manifest as pericoronitis of wisdom teeth, dental caries of wisdom teeth or adjacent teeth, periodontitis, pulpitis and other diseases in clinic, causing severe pain. Therefore, it is suggested that abnormal or asymmetrical wisdom teeth should be extracted as soon as possible.