Crowded teeth are caused by the fact that as humans evolve and chew finer and softer foods, the chewing force becomes less and less stimulating to the jawbone, causing the jawbone to become shorter and shorter the more humans develop. The number of teeth does not change, which means that the short dental arch can no longer accommodate too many teeth, resulting in crowded teeth. Crowded teeth have many hazards: 1, unattractive, uneven teeth, when smiling or speaking aesthetics will be greatly reduced; 2, uneven teeth, brush teeth is not easy to brush clean, brush unclean teeth will have some plaque buildup in the gum edge, will cause gingivitis. The plaque that accumulates around the gums for a long time produces calcification and forms calculus. The long-term presence of calculus will have a compressive effect on the periodontium and alveolar bone, and prolonged compression will lead to alveolar bone resorption, which is also known as periodontitis.