Crowded teeth can be directly observed by the naked eye and affect the personal image very much. The degree of dental crowding is generally classified as mild, moderate and severe, usually based on the difference between the sum of the width of all teeth and the circumference of the dental arch, as follows: 1. The difference between 0-4mm is called mild crowding; 2. The difference between 4-8mm is called moderate crowding; 3. The difference over 8mm is called severe dental crowding. Crowded teeth are the more common mis(dentition) malocclusion, which is manifested by the difference in the number and size of teeth and the length between the teeth bed. The number and size of teeth in modern people have not changed much from those in the past, but the dental bed is in a degraded state due to the finer diet and lack of food stimulation in modern people, i.e., the dental bed becomes smaller while the teeth do not change much, resulting in the dental bed being insufficient to accommodate the teeth, manifesting as dental crowding. The time to correct crowded teeth varies depending on the difficulty. Generally, it takes about 1.5-2 years to correct in children and adolescents, and about 2 years in adults, with some difficult cases taking longer.