The causes of brittle teeth are: 1, frequent bleaching or application of whitening drugs will cause the teeth to be corroded by chemicals, gradually becoming dry and losing elasticity. 2, when suffering from tetracycline or fluorosis, the teeth are affected by external drugs during the development process leading to structural loosening and brittleness. 3, after necrosis of the pulp occurs or root canal treatment removes the pulp, the teeth lose nutrients and water and become brittle easily. 4, when suffering from tetracycline or fluorosis, the teeth lose nutrients and water and become brittle easily. The tooth may become brittle and brittle after the pulp is necrotic or the root canal treatment removes the pulp. 4, Congenital underdevelopment of the enamel or under calcification reduces the mineralization of the enamel causing the tooth to split. 5, Eating hard food frequently can cause multiple cracks on the tooth surface and finally split completely.