When the milk teeth are straight and the permanent teeth are crooked after tooth replacement, under normal circumstances, it may be temporary misalignment during the period of mixed dentition, and in case of disease, it may be due to underdevelopment of jawbone, heredity and other factors, as follows: 1. Normal situation: temporary misalignment such as mild crowding, maxillary mesial incisor gap and maxillary lateral incisor skewing may occur during the period of tooth replacement, which may be adjusted to normal in the process of development. 2. Disease conditions: (1) Underdevelopment of jaws: long-term consumption of soft food may lead to underdevelopment of jaws, resulting in malocclusion such as crowding of permanent teeth. (2) Heredity: the presence of malocclusion in parents increases the probability of malocclusion in children, which may be manifested in the permanent dentition. There may be other reasons why the baby teeth are straight and the permanent teeth are crooked after tooth replacement, so it is recommended to go to the hospital in time to get a clear cause of the disease and then carry out targeted treatment.