Guided Tissue Regeneration, Periodontal: Techniques for enhancing and directing cell growth to repopulate specific parts of the PERIODONTIUM that have been damaged by PERIODONTAL DISEASES; TOOTH DISEASES; or TRAUMA, or to correct TOOTH ABNORMALITIES. Repopulation and repair is achieved by guiding the progenitor cells to reproduce in the desired location by blocking contact with surrounding tissue by use of membranes composed of synthetic or natural material that may include growth inducing factors as well.Guided Tissue Regeneration: Procedures for enhancing and directing tissue repair and renewal processes, such as BONE REGENERATION; NERVE REGENERATION; etc. They involve surgically implanting growth conducive tracks or conduits (TISSUE SCAFFOLDING) at the damaged site to stimulate and control the location of cell repopulation. The tracks or conduits are made from synthetic and/or natural materials and may include support cells and induction factors for CELL GROWTH PROCESSES; or CELL MIGRATION.Absorbable Implants: Implants constructed of materials designed to be absorbed by the body without producing an immune response. They are usually composed of plastics and are frequently used in orthopedics and orthodontics.Gingival DiseasesAlveolar Bone Loss: Resorption or wasting of the tooth-supporting bone (ALVEOLAR PROCESS) in the MAXILLA or MANDIBLE.Bone Regeneration: Renewal or repair of lost bone tissue. It excludes BONY CALLUS formed after BONE FRACTURES but not yet replaced by hard bone.Membranes, Artificial: Artificially produced membranes, such as semipermeable membranes used in artificial kidney dialysis (RENAL DIALYSIS), monomolecular and bimolecular membranes used as models to simulate biological CELL MEMBRANES. These membranes are also used in the process of GUIDED TISSUE REGENERATION.Gingival Recession: Exposure of the root surface when the edge of the gum (GINGIVA) moves apically away from the crown of the tooth. This is common with advancing age, vigorous tooth brushing, diseases, or tissue loss of the gingiva, the PERIODONTAL LIGAMENT and the supporting bone (ALVEOLAR PROCESS).Bone Substitutes: Synthetic or natural materials for the replacement of bones or bone tissue. They include hard tissue replacement polymers, natural coral, hydroxyapatite, beta-tricalcium phosphate, and various other biomaterials. The bone substitutes as inert materials can be incorporated into surrounding tissue or gradually replaced by original tissue.Regeneration: The physiological renewal, repair, or replacement of tissue.Nerve Regeneration: Renewal or physiological repair of damaged nerve tissue.Liver Regeneration: Repair or renewal of hepatic tissue.Tissue Engineering: Generating tissue in vitro for clinical applications, such as replacing wounded tissues or impaired organs. The use of TISSUE SCAFFOLDING enables the generation of complex multi-layered tissues and tissue structures.Tissue Scaffolds: Cell growth support structures composed of BIOCOMPATIBLE MATERIALS. They are specially designed solid support matrices for cell attachment in TISSUE ENGINEERING and GUIDED TISSUE REGENERATION uses.Biocompatible Materials: Synthetic or natural materials, other than DRUGS, that are used to replace or repair any body TISSUES or bodily function.Wound Healing: Restoration of integrity to traumatized tissue.Regenerative Medicine: A field of medicine concerned with developing and using strategies aimed at repair or replacement of damaged, diseased, or metabolically deficient organs, tissues, and cells via TISSUE ENGINEERING; CELL TRANSPLANTATION; and ARTIFICIAL ORGANS and BIOARTIFICIAL ORGANS and tissues.Animal Fins: Membranous appendage of fish and other aquatic organisms used for locomotion or balance.Stem Cells: Relatively undifferentiated cells that retain the ability to divide and proliferate throughout postnatal life to provide progenitor cells that can differentiate into specialized cells.Periodontal Ligament: The fibrous CONNECTIVE TISSUE surrounding the TOOTH ROOT, separating it from and attaching it to the alveolar bone (ALVEOLAR PROCESS).Mesenchymal Stromal Cells: Bone-marrow-derived, non-hematopoietic cells that support HEMATOPOETIC STEM CELLS. They have also been isolated from other organs and tissues such as UMBILICAL CORD BLOOD, umbilical vein subendothelium, and WHARTON JELLY. These cells are considered to be a source of multipotent stem cells because they include subpopulations of mesenchymal stem cells.