The period between 6 and 12 years old is the time when the baby teeth and permanent teeth are replaced, and it is during this period that misaligned teeth occur. There are many reasons for misaligned teeth, but the two main reasons are congenital and acquired, and the acquired reasons are more important. Congenital causes The growth and development of teeth are influenced by internal and external factors of the body. If the fetus is stimulated in the mother’s body, or if the mother is ill and malnourished during pregnancy, this can affect the normal development of the fetus’ teeth and jawbone, resulting in misalignment of teeth after eruption. Parents with unaligned teeth can also pass it on to their children. Acquired causes include the following: i. Incorrect use of rubber pacifiers. When feeding the baby, if the position of the bottle is too far up in front, or if the baby is supine for a long time, it will make the lower jaw suck forward, so that the lower jaw and the lower dental arch will move forward over time, and the upper dental arch will be pressed, forming the front teeth “envelope” malformation. Second, premature loss or retention of milk teeth can lead to uneven teeth growth. When the permanent teeth have not yet erupted, the teeth on both sides will shift to the gap and make the gap smaller, causing the permanent teeth to erupt later because they do not have enough position and are crooked, out and in. Third, tonsil enlargement or nasal cavity disease and make the nose breathe poorly, resulting in breathing through the mouth, and sleep with the mouth open. Due to the airflow through the mouth, the palate is subjected to upward pressure and cannot develop normally downward, so that the palate rises upward, the left and right sides of the upper dental arch also become narrower, the front part of the upper dental arch protrudes forward, the erupting front teeth not only tilt forward, and often misaligned, forming the face shape of the open lip and exposed teeth. Fourth, the impact of bad habits on teeth are as follows: 1, spit and bite the tongue: when the front teeth will erupt, there is a mild discomfort or itch on the dental bed, some children love to spit the tongue, lick the dental bed or bite the tongue. Over time, the formation of tongue, tongue-biting habits, so that the erupting teeth are blocked by the tongue, the upper and lower incisors can not contact each other, the formation of the incisor opening malformation. 2, tongue licking teeth: in the period of loose milk teeth, some children like to use the tip of the tongue to lick, and after the habit of licking the permanent teeth that just erupted, the teeth being licked by the outward thrust, the crown over time tilted to the front, fan-shaped open, the upper and lower lips are not easy to close, showing “open lips and teeth” deformity. 3, bite fingers or pencil: some children like to bite fingers, or pencil into the upper and lower teeth, resulting in the upper incisors protrude, the lower incisors move back, teeth become shorter, the upper and lower teeth do not contact, the teeth crowded uneven, manifested as small open deformity.