The last time James Cigelske had a tooth filled, the dentist didn't stab him with a needle full of novocaine. Instead, he used low-voltage current to kill the pain, saving the Milwaukee insurance agent from the usual "numb lips, nausea, unintelligible speech, and dinner on your shirt." Cigelske, who was pleasantly surprised by the treatment, was playing guinea pig for a new industry.

The electrical analgesia equipment was developed by Pain Prevention Inc., of Northfield, Ill., one of a number of companies hoping to cash in on the widespread antipathy to novocaine shots. Dentists seem eager to try the technique. Pain Prevention took home 52 orders and 362 requests for information when it displayed its $3,500 system at the American Dental Association convention last October.

A competitor, Hauser Laboratories, of Boulder, Colo., developed electrical analgesia with the help of a $50,000 contract from the Department of Defense, which frets over the welfare of millions of teeth each day. Hauser, which is primarily a research and development outfit, is looking for a partner to complete the development of the system and market it. A third company, Pain Suppression Labs Inc., of Elmwood Park, N.J., has arranged for a larger company to market the device it patented in 1976 but didn't have the funds to develop until recently. In the past year, the company has raised $1.5 million through private placements and has grown from 3 to 25 employees.

Scientists don't know for sure why electrical anesthesia works. Some theorize that nerve pathways that transmit pain get blocked when too many electrical signals try to squeeze through at once. Others say that electricity stimulates the body to release higher levels of serotonin, a biochemical present in the blood that makes patients less sensitive to pain. However they work, all three commercial systems allow patients to regulate the electrical stimulation to control pain.