A-PRF Article Gingival recession L-PRF Pouch and tunnel technique Semilunar vestibular incision technique adult advanced platelet rich fibrin clinical article clinical effectiveness clinical evaluation clinical laboratory clinical outcome controlled study disease classification double blind procedure female gingiva disease gingival index human intermethod comparison male medical documentation outcome assessment patient safety plaque index platelet-rich fibrin postoperative period randomized controlled trial semilunar vestibular incision technique with pouch