There are many causes of cracks in the middle of the teeth, the common ones are dental caries, intradental resorption, and dental invagination. 1. Dental caries: due to the role of chronic bacterial infection, resulting in chronic progressive destruction of the hard tissues of the teeth, the teeth become weak, causing cracks in the teeth, cracks can be aggravated when biting hard objects. 2. Intradental resorption: Normal pulp tissue becomes granulation tissue, in which osteoclasts start absorbing dental hard tissues from the inside of the pulp cavity, making the wall of the pulp cavity thinner, which can result in cracks in the middle of the tooth, root perforation, and so on. 3. Dental invagination: During the period of dental development, abnormal development of enamel-forming apparatus caused by abnormal development of tooth morphology, after the tooth eruption, there can be a cystic deep-set cavity on the tooth surface, which can be caused by bacterial growth to form caries leading to cracked teeth. There may be other reasons for cracking in the middle of the tooth, such as pulpless teeth, etc. It is recommended to go to a specialist hospital in time and standardize the treatment to prevent further fracture of the tooth.