Neuromuscular dentistry is name for a bite and TMJ disorder treatment philosophy that has succeeded in marketing a diagnostic package in spite of good science showing that it provides no clinically useful information. It was invented during the 1980's by a popular dental researcher who thought he had found a technique that would identify the perfect bite - the holy graile of dentistry. His technique involved placing a pulsing TENS (transcutaneous electrical nerve stimulation) machine that produces tiny electrical shocks directly over the motor root of the jaw muscles. His theory was that it would fire all the jaw muscles evenly and thereby locate the ideal position for the lower jawbone.
Dr. Jankelson successfully marketed his pulsing TENS machine along with a jaw tracking device and a surface EMG detector in a diagnostic package he called “neuromuscular dentistry” and promoted by the slogan, "If it has been measured, it's a fact. If it has not been measured, it's an opinion." When Dr. Jankelson was near the end of this life, the ADA gave his equipment its seal of approval. Then he died and a flood of scientific research was published showing that the equipment did not fire all the jaw muscles evenly, and clinically it was unable to even distinguish between patients and healthy people. Anatomical studies using needle electrodes showed that the pulsing TENS simply stimulates firing of the muscle fibers that are closest to the source of the TENS.
However, when the ADA went to withdraw its approval, it was sued by all the dentists who had bought the equipment based on their recommendation. Thus the ADA will never be able to withdraw its approval. The FDA cannot regulate the equipment, because the FDA only evaluates safety and efficacy. The diagnostic equipment is certainly safe. It is also effective at measuring what it measures, even if those measurements are clinically useless. Meanwhile the company has become increasingly effective at marketing the product to dentists - along with all necessary practice management tools for billing and communicating with insurance companies, local doctors, and media.
The equipment sometimes works clinically, but not for the reasons it's supposed to. TENS is used in medicine to provide pain relief, not muscle relaxation, and there is no good evidence that it actually relaxes the jaw muscles. Any relaxation of the jaw muscles brought about by TENS treatment would be most likely a secondary effect of diminishing the pain, because anything that diminishes pain relaxes muscles. Applying TENS over the cheeks usually causes the lower jawbone to shift anteriorly, because the muscles closest to the source are the superficial masseters, which are oriented in a more forward direction than the other elevator muscles. Treatment that brings the lower jawbone forward often provides relief of symptoms, because many TMJ disorders are caused by a jawbone that is located too far backward, not because TENS has some special ability to relax the jaw muscles.