Guided Tissue Regeneration

Nov. 1, 2001
Tissue engineering offers promise for reconnecting periodontal ligament fibers to bone.

Tissue engineering offers promise for reconnecting periodontal ligament fibers to bone.

by Cathleen Terhune Alty, RDH

The thought of tissue engineering may bring visions of Mr. Whipple and those old TV commercials to your mind. But the subject is human tissue engineering and regeneration, which may just be a quantum leap in all of medicine. Regenerating cementum and periodontal ligament fibers to reconnect and re-anchor tooth to bone, as well as growing donor tissue in the lab for grafts, is at the true cutting edge of periodontics today.

Tissue engineering is the "development and manipulation of lab grown molecules, cells, tissues, or organs to replace or support the function of defective or injured body parts," according to Advanced Tissue Sciences of La Jolla, Calif. By combining biology and engineering, this company is producing complex, three-dimensional tissues that literally integrate with a patient's body. Although skin grafts have been grown for more than 10 years, this engineering process that allows more complex cell growth is truly amazing.

Dr. Michael McGuire, a periodontist in Houston, Texas, calls tissue engineering "off the shelf body parts." He is involved in the first FDA-approved study that uses this new tissue to re-grow attached gingiva.

"This first study is very basic," said Dr. McGuire. "We're just trying to see if it can be done! We have to walk before we can run."

Dr. McGuire is studying if this grown tissue, which is called Dermagraft™, will grow attached gingiva. He claims that, so far, things look very positive on the dozen or so patients he has treated for the study.

Incredibly, it's not fiction
Briefly, the donor tissue is grown in a biocompatible 3-D mesh sheet. One donor can grow 250,000 square feet of tissue (the length of six football fields). This tissue is living tissue that can be frozen and thawed out, cut to size, and placed in the mouth. Dr. McGuire sutures it into place, and, because it is so full of a variety of growth factors, he says it can "communicate" with the host tissue to determine what it needs to manufacture for the healing process to begin.

"I know it sounds like science-fiction," he says, "but I fully expect this to revolutionize dentistry. Instead of a root canal, we'll remove the diseased one and regrow the nerve. We'll regenerate enamel and cementum as well." Dr. McGuire says that more study is needed to discover if this new procedure is safe and effective, but it offers a fascinating glimpse into tissue engineering. There are other medical studies to attempt to grow knee cartilage and other body parts for replacement.

Surgically creating new bone structure to replace what has been lost to disease has been available for many years. The problem is that the epithelial cells from the gingival tissue grow faster during healing than the cells that would reform the cementum and periodontal ligament (PDL). In this race to attach, the epithelial cells win every time and will literally grow down the "wall" between the bone and the tooth root surface. The epithelial tissues do loosely attach to the root, but this attachment is not anything like the former attachment by PDL fibers. This epithelial attachment will often "unstick" from the root and the pocket reappears.

To change the odds of the race a bit, a barrier membrane has been developed that will prevent the faster moving epithelial cells from advancing down into the pocket. This helps the slower cells to establish themselves while making new cementum and PDL fibers. The procedure of using a barrier membrane to block epithelial cells is called "guided tissue regeneration" or GTR. Literally, the desired tissues are being protected to form while the others are being excluded via a barrier. These thin barriers are placed in a collar around the tooth following debridement under a gingival flap elevation. The gingival tissue is laid on top of the barrier, and the gingiva is sutured. If the barrier is resorbable, it will slowly disintegrate in six to eight weeks. If nonresorbable, a second surgical procedure is required several weeks later to remove the barrier.

Some unique challenges face dental hygienists who are caring for patients who have undergone GTR. Dr. Robert Del Castillo, a periodontist who practices in Miami Lakes, Fla., details the hygiene protocol for patient management. First of all, plaque control is critical for success of the procedure. The problem is that the patient is instructed not to brush the area.

"We instruct patients not to brush because it can lead to abrasion and exposure of the membrane, which can compromise the effectiveness of the procedure," says Dr. Del Castillo. "We instruct the patient to rinse with a chlorhexidine rinse twice a day, and no flossing or subgingival irrigation is permitted for six months post surgery. The patient returns weekly until the sutures are removed."

During the weekly visits, a hygienist evaluates plaque removal and may do a coronal non-abrasive polish with a baking soda and chlorhexidine slurry. A very gentle scaling may be required around the surgical area if plaque is accumulating. Additional homecare instructions may be given if the patient is having difficulty with plaque control.

The barrier also needs to be left as stable and motionless as possible. During the healing process, Dr. Del Castillo says it is very important for the wound to be stable. "Studies have shown that even a micro-movement of 10 to 20 microns disturbs the new cells."

Dr. Del Castillo says that removable prosthetics should be adjusted so there is no pressure on the site. "If the surgery is for ridge augmentation, the patient should not wear prosthetics for one month."

As far as checking on the patient's progress, there can be no periodontal probing for at least six months. The probe could dislodge or move the membrane, or break any newly forming PDL fibers. Radiographic evidence of new bone growth may be visible after six months, but sometimes it takes as long as 12 months.

Dr. Del Castillo says that if a dentist or hygienist has any doubt at all about a post-surgery patient, they should call the periodontist. He says, "You can't expect patients to know what was performed, and general dentists can't know unless the periodontist tells them."

Technology is offering some new alternatives to traditional approaches to periodontal problems, and with it will come questions of ethics, safety, and effectiveness. One thing is clear — today's science fiction may be tomorrow's treatment of choice.

Cathleen Terhune Alty, RDH, is a frequent contributor who is based in Clarkston, Michigan.