Crowded teeth are generally clinically classified into three degrees: 1, degree I: the crowdedness of the dental arch is about 2-4mm; 2, degree II: the crowdedness of the dental arch is 4-8mm; 3, degree III: the crowdedness of the dental arch is more than 8mm. Normal teeth are arranged neatly one by one, but patients with crowded teeth tend to have their teeth crowded and twisted, and the gap needed to align these crowded and twisted teeth is the crowding degree. The amount of space needed to align these crowded and twisted teeth is the degree of crowding. The amount of space needed for normal uncrowded teeth and the amount of space available in the crowded arch are subtracted from each other, which is the approximate degree of crowding.