The temporomandibular joint, or TMJ, is where the jawbone connects to the skull, and according to the National Institute of Dental and Craniofacial Research, nearly 11 million Americans suffer from TMJ disorders.
Though the precise cause of many TMJ disorders remains a mystery, symptoms can range from minor and occasional pain due to clenching the jaw or grinding the teeth to severe, debilitating pain that requires hospitalization or surgery. Because the TMJ is essential for basic functions like speaking, chewing and swallowing, TMJ disorders can seriously degrade people's quality of life and lead to severe depression.
A central feature of the TMJ is a thin sheet of cartilage about the size of a postage stamp that sits between the mandible and the skull. Called the TMJ disc, this sliver of cartilage cannot heal itself if it is injured or damaged. Approximately 70 percent of all TMJ disorders result from TMJ disc displacement, and there are no synthetic materials that can replace a damaged or injured TMJ disc.
Rice's new TMJ tissue engineering program aims to develop methods for growing replacement TMJ discs that can be implanted without risk of rejection because they will be grown from a patient's own cells.
"Our project marks the first time that a research group has tried to engineer the entire TMJ disc in vitro in the laboratory," said Kyriacos Athanasiou, the Karl F. Hasselmann Professor of Bioengineering at Rice and the principal investigator on the NIH grant. "This is a tall order because there is scant information about what the TMJ disc is, what it is made of, what its functions are, what its pathologies are and how its pathologies develop."
Athanasiou's Musculoskeletal Bioengineering Laboratory specializes in growing cartilage tissues. There are projects under way to grow articular cartilage -- which accounts for about half of all cartilage in the body -- as well as more specialized types like the knee meniscus. Like the TMJ disc, the knee meniscus is a disc that separates bones in a major joint. Both the TMJ disc and the knee meniscus are unique, with different properties than any other cartilage in the body, but unlike the meniscus, the properties of the TMJ disc -- its compressive and tensile stiffness, for example, or the proportion and types of collagen it contains -- are largely unknown.
Athanasiou and colleagues have been laying the groundwork for the TMJ tissue engineering program for four years. Earlier this year, he and his students published a review of the complex biochemical, biomechanical and cellular properties of the joint disc and the challenges these properties pose for tissue engineering approaches to reconstruction. In the early stages of the tissue engineering program, Athanasiou's team will continue to characterize and compare tissues grown from adult animal cells.
In growing their samples, Athanasiou's team will sort out the complex regime of biomechanical cues and growth factors that are needed to coax cells into producing TMJ cartilage. They expect that a combination of mechanical stimuli and biochemical signals will be needed in order to make the tissue grow properly. Following a systematic experimental design, they will try various combinations of stimuli and growth factors to determine the best regime for growing TMJ discs that are suitable for surgical implantation.
"I have served as a scientific adviser to an advocacy group called the TMJ Association for several years, and I've gotten a glimpse of the pain and suffering that TMJ patients endure on a daily basis," Athanasiou said. "It is my fervent hope that our work can help some of these people live normal and pain-free lives."