Pain and pain management have long been items of central concern in dentistry. Although they are given little attention in orthodontics, virtually every patient wearing orthodontic appliances experiences and complains of some extent of pain, and someones have suffered from severe throbbing pain. A form of stimulation-produced analgesia, Transcutaneous Electrical Nerve Stimulation (TENS) is a non-invasive, non-pharmacologic pain control techniques. The clinical application of TENS to orthodontic patients may lead to better patient compliance. And I want to discuss some basic knowledge of this TENS.