In the process of orthodontics, mild pain will be felt at first, which is a normal reaction and can be tolerated by most patients. This slight pain is often accompanied by orthodontic treatment, which is also an effective performance of orthodontic treatment. When a tooth is subjected to a slight and continuous external force from the orthodontic appliance, the tooth itself will not be painful, but this force will make the periodontal ligament between the tooth and the alveolar bone crowded and pulled.

The periodontal ligament, which connects the teeth with the alveoli, is composed of nerves, blood vessels and cells. When the tissue is deformed by stress, the blood circulation is blocked, forming a state of hypoxia. At this time, the surrounding cells will release some nerve conduction substances to stimulate the nerves. At first, the concentration of these substances is very low, which is not enough for people to feel pain. It is only 5-6 hours after the orthodontic appliance is installed that its concentration is enough to cause the feeling of pain.