The causes of wide gap between baby teeth are as follows: First, the structure of milk teeth is characterized by a significant narrowing of the cervical part of the tooth, and the crown of the tooth near the cervical part of the 1/3 bulge, which can form a large gap between the two teeth. Second, when the baby’s labial or lingual tie is attached too low, it can affect the closure of the gap between the upper and lower middle incisors, and phenomena such as unclear pronunciation occur. Third, when caries damage is formed on the adjacent surfaces of baby teeth, the caries cavities keep expanding, and the dental tissues on the jaw surface are easy to collapse, resulting in a large gap. Fourth, milk teeth often embedded food fibers, will press the gums and alveolar bone resorption, resulting in a triangular gap. Fifth, with the continuous development of the baby’s jawbone, the length and width of the dental arch gradually increased, and the gap between the milk teeth also increased, in preparation for the eruption of permanent teeth.