Multiple teeth and congenitally missing teeth and others II. Abnormal tooth development or position 1. The incidence is about 1/110, and the ratio of maxillary to mandibular is 1/8, mostly in the area of maxillary anterior teeth, such as between the central incisors when there are several, some grow out of the interdental, some buried in the jawbone. Patients with cleft palate almost always have multiple teeth, and there are various forms, such as conical, normal tooth-like and cuspid-shaped. Harmful effects: obstructing the normal position of the adjacent teeth from erupting or closing the orthodontic space; causing misaligned growth, twisting and crowding of the adjacent teeth, which can be buried in the jawbone, and some develop into a swelling. Patients with cleft palate almost always have multiple teeth, 2, congenitally missing teeth seen clinically: its incidence is about 4%, can cause gaps and deep lining. The missing teeth are mostly found in the lower central incisors, followed by the upper lateral incisors and bicuspids, etc. In a few cases, there are multiple missing teeth and the whole jaw is missing, the hazards: easy to produce a dental gap causing abnormal tongue habits and language pronunciation; the upper teeth are missing when the arch length development is limited causing the occurrence of inwardly inclined deep lining, the lower teeth are missing causing anteriorly protruding deep lining, and even causing facial abnormalities. The impact of edentulism is even greater in the absence of teeth in the whole jaw. 3, abnormal tooth morphology, clinical findings: oversized teeth, fused teeth, undersized teeth and malformed cusps, etc. Harmful: can cause obstacles to the arch length and lined relationship, causing crowding or gaps; malformed lingual cusps of anterior teeth and malformed central cusps of bicuspids, which may be in early contact with the lined teeth, resulting in displacement, and may also injure themselves, 4, retained milk teeth and bony adhesions Clinical: the difference between the two is that when bony adhesions occur in the latter, they can be seen to be significantly lower than the adjacent teeth by 1 to 3 mm, with the adjacent teeth tilted and the lined teeth elongated In the latter case, the bony adhesions are significantly lower than the adjacent teeth by 1 to 3 mm, the adjacent teeth are inclined, and the lined teeth are elongated. The former can be different depending on the cause, and can lead to ectopic eruption of subsequent permanent teeth, and may also cause lined chewing due to pain; in the absence of subsequent permanent teeth, it can remain in the original position for decades. The effect of the latter is mainly to cause the neighboring teeth to be tilted and the lined teeth to be elongated, which can easily lead to temporomandibular joint disorders caused by lined trauma and movement disorders. 5. Ectopic eruption of the maxillary first permanent molar. Clinically seen: due to the proximity of the maxillary first permanent molar tilted eruption. Hazardous: It presses the distal root of the second molar to resorb, resulting in early loss of the second molar, and causes obstruction or misalignment of the second bicuspid due to insufficient space. It can also be seen that the mandibular first permanent molar erupts lingually ectopically, and can also cause locking and antilining of individual posterior teeth. 6, orthodontic gap, also known as orthodontic separation Clinical: specifically refers to the gap between the two maxillary central incisors, due to the upper lip tethered attachment is too low or multiple teeth, so that the orthodontic gap can not be closed, the upper lip tethered attachment is too low clinical examination is simple and easy to operate, when lifting the upper lip to observe whether the tethered attachment linkage involves the gingival papilla between the central incisors, the gingival papilla has a degree of movement, it indicates that the attachment is too low; when the orthodontic gap is not related to the upper lip tethered, should be When the median gap is not related to the upper labial tether, it should be considered that there are multiple teeth buried between the upper and middle incisors, and the diagnosis should be clarified and differentiated from the scattered gap caused by the tongue habit by taking x-ray films. 7, ectopic ambiguous teeth clinical seen: permanent teeth lined at the beginning of the corresponding milk teeth have been replaced by permanent teeth, and one of the tooth position has a gap without teeth or any retained milk teeth, and there is no sign of shedding, by taking X-ray film to check the situation of retained teeth and permanent teeth can confirm the diagnosis, and even as many as several. Most commonly seen in upper cuspids, upper central incisors and second bicuspids ectopic ambiguous, harmful: easy to cause adjacent teeth to shift to the gap, resulting in the loss of normal tooth position; multiple teeth ambiguous, the crown overlap bone loss, the mouth is easy to induce bad tongue habits. Except for the second bicuspid obstruction which is caused by the near-medial displacement of permanent molars or periapical disease of the first molar, most of the other incisors and cuspids have curved root ends and are hooked in severe cases.