Guided tissue regeneration (GTR) is a specialized surgical technique in dentistry designed to promote the growth of new bone and periodontal tissues following damage caused by disease or injury. When a tooth’s supporting structure is lost, the body’s natural healing process often results in the formation of scar tissue rather than the intended bone and ligament. The use of resorbable barriers provides a temporary framework that directs which cells are allowed to populate the defect site, allowing for predictable healing and reconstruction of the tooth-supporting apparatus.
The Principle of Guided Tissue Regeneration
The necessity of Guided Tissue Regeneration stems from a biological competition for space during healing. Following bone loss, the gum tissue contains fast-growing epithelial and connective tissue cells. These cells rapidly migrate downward into the defect, effectively outcompeting the slower-growing cells responsible for creating new bone, cementum, and periodontal ligament. This soft tissue invasion results in poor quality repair, often leading to a fragile attachment or a non-supportive fibrous scar tissue filling the defect.
The core function of the GTR barrier is to act as a physical separator, creating a protected space over the defect. This barrier excludes the unwanted, fast-moving gingival cells from entering the area beneath it. By reserving this space, the barrier allows desired cells—specifically osteoblasts (bone-forming cells) and periodontal ligament progenitor cells—the necessary time to slowly populate the defect and lay down new supporting structures.
Composition of Resorbable Barrier Materials
Resorbable barriers are favored over older, non-resorbable materials because they safely dissolve within the body, eliminating the need for a second surgery to remove them. These materials are broadly categorized into natural and synthetic polymers, each designed for biocompatibility and controlled degradation. A common type is purified collagen, typically derived from porcine or bovine sources, which is highly compatible with human tissue. Collagen membranes promote blood clot stabilization and integrate well with the surrounding tissues.
Synthetic resorbable barriers are usually made from aliphatic polyesters, such as polylactic acid (PLA), polyglycolic acid (PGA), or their copolymers (PLGA). These materials break down safely through hydrolysis, a process where water molecules slowly cleave the polymer chains. The resulting breakdown products are simple, non-toxic molecules like lactic acid and glycolic acid, which the body metabolizes and excretes. Manufacturers adjust the composition and structure of these polymers to precisely control the membrane’s mechanical properties and degradation rate.
How the Barrier Directs New Tissue Growth
The success of a resorbable barrier relies on its physical properties while it remains intact, not just its ability to dissolve. The barrier must maintain structural integrity for a sufficient period, known as the “barrier phase,” to prevent collapse into the defect. This space-maintaining function is paramount, as a collapsed membrane fails to reserve the volume needed for new bone and ligament growth. The rigidity and thickness of the membrane are engineered to withstand the pressure of the overlying soft tissue.
The barrier must also be semi-permeable to support the active healing process beneath it. It must allow for the passage of nutrients, oxygen, and growth factors from the surrounding blood supply to reach the regenerative cells in the protected defect. Simultaneously, the material’s pore structure must be dense enough to physically block the migration of larger, unwanted epithelial and connective tissue cells. The barrier essentially creates a protected, nutrient-rich scaffold where the slower-moving progenitor cells can successfully migrate and mature.
Clinical Applications and Resorption Timeline
Resorbable GTR barriers are used in several common clinical scenarios where bone or periodontal support needs to be reconstructed.
Clinical Applications
A primary application is treating deep periodontal bone defects around existing teeth, where the goal is to regenerate the lost periodontal ligament, cementum, and alveolar bone. They are also routinely used for socket preservation, which involves placing the barrier over an extraction site to prevent the socket walls from collapsing and to maintain bone volume before a dental implant is placed. Furthermore, they are applied in Guided Bone Regeneration (GBR) procedures to augment bone mass in preparation for dental implants in areas of insufficient bone height or width.
Resorption Timeline
The timeline for material degradation is specifically tailored to match the body’s healing rate for the particular tissue being regenerated. For most collagen membranes, the barrier function—the physical exclusion of soft tissue—is maintained for approximately four to six weeks, which is when the overlying gum tissue heals and establishes its own barrier. Complete resorption of the material takes much longer, typically ranging from a few weeks to several months, depending on the material’s composition and cross-linking. Some synthetic polymer membranes maintain their integrity for up to 20 weeks, with full bioresorption occurring between six and twelve months. Post-operative care involves strict hygiene protocols to prevent infection, which could cause the barrier to degrade prematurely.