Multiple teeth can be harmful in several ways and usually need to be extracted. 1. First of all, supernumerary teeth can affect the alignment of permanent teeth. Under normal circumstances, permanent teeth are arranged in an orderly manner, each occupying its own position. The appearance of supernumerary teeth will disrupt the arrangement of permanent teeth. 2. Secondly, supernumerary teeth will affect the development of permanent teeth. Due to the emergence of supernumerary teeth, it will cause crowding of permanent teeth, which will lead to the obstruction of permanent teeth, delayed eruption of permanent teeth, and affect the development of permanent teeth. 3. Finally, supernumerary teeth may cause oral diseases. Long-term buried supernumerary teeth can cause cysts in the jawbone, root resorption and other lesions. It is best to go to the regular hospital in time and have the supernumerary teeth extracted as soon as possible.