After a 10-year clinical trial of a jaw joint replacement developed by Peter Quinn of the University of Pennsylvania School of Dental Medicine, the Food and Drug Administration has given it a thumbs-up.
Because of almost ceaseless motion a human jaw moves about 700,000 times a year as a person chews, talks, swallows and yawns the jaw, or temporomandibular joint, can become a problem for as many as 20 million Americans, said Quinn, chairman of oral and maxillofacial surgery at Penn Dental Medicine. Teeth grinding and injuries also take their toll.
"Temporomandibular disease is almost a uniquely female disease. Almost 90 percent of the people in the trial were female, and most had TMD as a result of slippage of a disc in the joint," Quinn said. "TMD in male patients is mostly due to injury."
"What we set out to do was get approval for a stock prosthesis," said Quinn, whose stock device is the first in history to get FDA approval through a rigorous pre-market approval process.
In 1991, Quinn paired with an orthopedic company called Biomet to design the appliance and do the requisite materials testing. Biomet later acquired a maxillofacial surgical company, W. Lorenz Surgical Inc., and the prosthesis is marketed as the Lorenz TMJ replacement system. The clinical trials got under way in 1995 at Penn, where 75 percent of the surgeries were performed, and UT Southwestern Medical in Dallas, TX, which accounted for the rest. The trials involved 285 patients and 403 joints. Both joints were replaced in some patients.
Quinn's TMJ prosthesis is constructed of the materials found in the more common knee and hip replacements, a polyethylene socket and a cobalt-chromium-molybdenum alloy ball, which avoids s high wear-rate problems but presents other challenges, such as its mechanics. Unlike knees and hips, the jaw moves differently by coming out of the socket, and each joint contains a disc that can slip or wear down. Also, it is much harder to fit a stock prosthesis in the jaw since the bone structure doesn allow much room.
"The socket is only a millimeter or two from your brain, is very thin in the middle and has this bump that differs from person to person," Quinn said. "So we flattened the design to eliminate the bump, created three different sizes and enabled the device to be screwed into the cheek bone."
The Lorenz prosthesis is already approved for use at two sites in Canada and eight in Europe, where Quinn has trained the surgeons. There will be 12 to 20 sites in the U.S. and six in South America.
"We had an agreement with the FDA that it would be approved with the condition of training, so it couldn just be sold," Quinn said. "You want surgeons who do enough of these since it is so technique sensitive. We are identifying surgeons who do a lot of TMJ surgery through the American Society of Temporomandibular Joint Surgery."
Recuperation from the procedure takes four to six weeks.