In the daily outpatient practice of oral and maxillofacial surgery, some people often ask their doctors whether “wisdom teeth should be extracted”. Then we should first understand what wisdom teeth are, which wisdom teeth pose a threat to the oral cavity and health and should be removed, and which wisdom teeth can be retained. 1, the origin of wisdom teeth Wisdom teeth refers to the human oral cavity, the alveolar bone on the last side of the upper and lower third molars, the ancient name “real teeth” “wisdom teeth” commonly known as the “riser teeth”. Because wisdom teeth usually begin to erupt at the age of about 20 years old, when the psychological and physiological development of people gradually mature, so the name of “wisdom teeth”. 2, the causes of wisdom teeth obstruction and its complications As we all know, “the use of waste” is a universal law in the theory of biological evolution. Wisdom teeth are an excellent example of this. In the process of human evolution, the structure of food from coarse to fine, from hard to soft, from raw to cooked has changed greatly, resulting in the weakening of chewing function and the gradual degeneration of chewing organs. The human teeth become round and blunt, the jawbone also recedes and becomes smaller, and is relatively underdeveloped, because the alveolar bone is the direct supporter of the teeth, and is most directly affected by the declining function of the teeth, so it degenerates the most, and still has to arrange 32 teeth, which is naturally crowded, and this is the main factor for the occurrence of dental misalignment and wisdom teeth obstruction. So what are the complications of wisdom teeth obstruction that can bring harm to our oral and general health? (1) wisdom teeth pericoronitis because the wisdom teeth can be forward, vertical, horizontal, inverted and other different directions of eruption, the crown can not be fully exposed, often covered by its surrounding gingival tissue, forming a gingival blind pocket, the pocket is very easy to retain food residues and harbor a large number of bacteria, when the jaw teeth bite the crown on the gingival flap or climate change, tension, fatigue, cold and other resistance to decline, easy to cause infection, the development as an acute wisdom teeth Pericoronitis, manifested as local gingival pain, redness and swelling, pus overflow, restricted mouth opening, swallowing difficulties, maxillofacial swelling, generalized fever, and even complications of osteomyelitis of the jaws. If not treated in time and the source tooth is removed, the infection often recurs and may spread and cause more widespread infection in the surrounding tissues. (2) Perimandibular interstitial infection If pericoronitis is not controlled by timely treatment or extraction, the inflammation can spread through its loose connective tissue to the surrounding soft tissue anatomical gaps of the jaw face, forming a perimandibular interstitial infection. The local manifestations may vary depending on the site of infection, but they have common features: rapid onset of the disease, significant congestion, swelling, fever, pain and various dysfunctions in the corresponding areas of the maxillofacial soft tissues, such as difficulty in opening the mouth when the inflammation stimulates the masticatory muscles, difficulty and pain in swallowing when the inflammation invades the pharyngeal side, difficulty in breathing due to compression of the epiglottis when the floor of the mouth is infected, restriction of tongue movement and slurred speech when the sublingual space is infected. The systemic symptoms are more obvious and even cause sepsis, which is life-threatening. (3) Osteomyelitis of the jaws Osteomyelitis of the jaws is often accompanied by infection of the perimandibular space, and when the inflammation spreads to the deeper bone marrow cavity, osteomyelitis is formed. The spread of inflammation in the bone marrow cavity generates pressure, severe jaw pain and multiple tooth pain, and if the inflammation invades the inferior alveolar nerve there is numbness of the lower lip. Dissolution and destruction of bone appears as multiple teeth loosening. The bone cortex is penetrated and the pus breaks away to form a facial fistula, often leaving a maxillofacial deformity. In the chronic stage of osteomyelitis of jaw, the jaw bone is mainly destroyed, and even pathological fracture, defect and dislocation occur, and the disease lasts for several months, and other loose teeth are often extracted in addition to the blocked wisdom teeth during treatment. (4) Adjacent tooth caries The carious damage of distal cervical part of adjacent teeth (mandibular second molar) is most common, often caused by anteriorly inclined or horizontally blocked wisdom teeth, because the cavity is hidden, it is not easy to be detected at an early stage, and the late stage of distal carious damage of adjacent teeth is often severe pain due to pulpitis. The interdental bone resorption is asymptomatic and often comes to the clinic only when the adjacent teeth are loosened or need denture repair at the late stage of bone resorption, and often must be extracted because it is too late. Therefore, the premature loss of adjacent teeth is often the main cause of premature loss in middle-aged and elderly people with anterior jaw position and horizontal group of wisdom teeth. The loss of this adjacent tooth has a greater impact on the chewing function and is very difficult to restore. (5) Resorption and bone resorption of the adjacent teeth When the embryo of the wisdom tooth does not have sufficient jaw bone during development and the eruption process is hindered, the compression and erosion of the wisdom tooth often leads to root resorption of the adjacent teeth (second molars), or inflammatory resorption of the alveolar bone due to periodontitis that often exists between the obstructed wisdom tooth and the adjacent teeth. (6) Temporomandibular joint disease The temporomandibular joint can flexibly open and close the mouth and participate in a variety of physiological functions such as chewing, pronunciation and expression under the synergistic action of the occlusal, temporal, internal and external pterygoid muscles. Wisdom teeth obstruction or misalignment of the mandible often affects the normal movement of the temporomandibular joint and causes temporomandibular joint disease. The main manifestations are joint popping, pain, and abnormal jaw movement. The pain of masticatory muscles is often accompanied by headache, tinnitus, and tongue pain. (7) Malocclusion Due to the relative underdevelopment of jaw bone during the most active period of wisdom tooth eruption, it is not possible to provide enough space for eruption. The propulsive force of wisdom tooth eruption affects the neighboring teeth (second molars), and the neighboring teeth (second molars) become twisted and misaligned, resulting in malocclusion and a significant decrease in masticatory function. (8) Odontogenic jawbone cyst If an obstructed wisdom tooth is present, the follicular sac is also present. Although in most cases no change occurs, there is a possibility of cystic transformation and becoming odontogenic cysts and odontogenic tumors. When the cyst develops to a certain extent, the jaw bone will be deformed, and in serious cases, pathological fracture will occur. (9) Pre-cancerous lesions of oral mucosa The gingival and buccal mucosa covering the obstructed wisdom teeth often have traumatic ulcers, white spots, abnormal hyperplasia and other lesions due to long-term mechanical stimulation or repeated bites, which interfere with the normal keratinization of the mucosal epithelium and cause pre-cancerous lesions, thus inducing mucosal carcinoma. 3. Suitable age for wisdom tooth extraction Because of the special characteristics of most wisdom teeth and the threat to the oral cavity and health, they should be extracted in time. So what is the right age for wisdom teeth extraction? Most experts believe that it is most appropriate to remove blocked wisdom teeth around the age of 20. During this period, pericoronitis is not in high incidence, the neighboring teeth have not accumulated food for a long time, and distal caries and interdental bone resorption of neighboring teeth rarely occur. At this time, the periodontal space of wisdom teeth is wide and the surrounding bone is loose, so there is less resistance to extraction. In actual clinical work, there are more patients aged 25-40 who have their wisdom teeth extracted, because this is the period of high incidence of pericoronitis and pulpitis of neighboring teeth, and the wisdom teeth are often extracted because of the damage of the distal mesial caries of neighboring teeth or excessive bone resorption between neighboring teeth, but it has caused irreparable damage to the neighboring teeth, so it is recommended to do prophylactic extraction for patients around 20 years old who are not suitable for retention. For the wisdom teeth that can bear the normal chewing function, we should consult the dentist in time to understand the development of wisdom teeth and decide the proper treatment of wisdom teeth by combining modern orthodontics and prosthetics.