# What is guided tissue regeneration?
A. A soft tissue graft used to correct mucogingival junction involvement
B. Placement of non-resorbable barriers or resorbable membranes and barriers over a bony defect
C. A free gingival graft used to increase the amount of attached gingiva
D. Placement of an autograft to treat a bony defect

The correct answer is B. Placement of non-resorbable barriers or resorbable membranes and barriers over a bony defect.

The method for the prevention of epithelial migration along the cemental wall of the pocket that has
gained wide attention is guided tissue regeneration (GTR). This method is based on the assumption that only the periodontal ligament cells have the potential for regeneration of the attachment apparatus of the tooth. GTR consists of placing barriers of different types to cover the bone and periodontal ligament, thus temporarily separating them from the gingival epithelium. Excluding the epithelium and the gingival connective tissue from the root surface during the postsurgical healing phase not only prevents epithelial migration into the wound, but also favors repopulation of the area by cells from the periodontal ligament and the bone.

The initial membranes developed were nonresorbable (polytetrafluoroethylene [PTFE]) and therefore required a second, although frequently simple, procedure to remove it. This second procedure was done after the initial stages of healing, usually 3 to 6 weeks after the first intervention. The second procedure was a significant obstacle in the uti lizat ion of this GTR technique, and therefore resorbable membranes  were developed.

Resorbable membranes marketed in the United States include OsseoQuest (Gore), a combination of
polyglycolic acid, polylactic acid, and trimethylene carbonate that resorbs at 6 to 14 months; BioGuide (OsteoHealth), a bilayer porcine-derived collagen; Atrisorb (Block Drug), a polyactic acid gel; and Biomend (Calcitech), a bovine Achilles tendon collagen that resorbs in 4 to 18 weeks. Of these, BioGuide is easier to use and generally preferred.

Currently. regenerative procedures are applicable and predictable under a certain set of circumstances:
(1) The patient exhibits exemplary plaque control both before and after regenerative therapy, 
(2) The patient does not smoke, 
(3) There is occlusal stability of the teeth at the regenerative site,
(4) Osseous defects are vertical in nature, with the more walls of bone remaining increasing the likelihood of regenerative success.

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