This prospective, randomized and controlled clinical trial will compare: CAF +1 mm thick L-PRF membrane versus CAF +2 mm thick L-PRF membrane for the treatment of RT1 gingival recession. From each patient a single recession on a single tooth will be selected. Clinical parameters will be evaluated at base-line and after 6 months.

The protocol is approved by the "G. D'Annunzio" University Ethical Committee. This study is in accordance with the Declaration of Helsinki of 1975. Patients will be recruited from the Unit of Periodontology, "G. D'Annunzio" University of Chieti-Pescara, Italy. All the volunteer candidates will sign a written informed consent.

The trial director will be responsible for randomly assigning patients to treatment after enrollment and will not involve with the clinical interventions or the study measurements. A computer-generated table will be used to make the random assignment, known only to the trial director. An opaque envelope will conceal group allocation and will be opened just before the intervention surgery. Matching between group and treatment will be performed by a figure extraneous to the experimentation, responsible even for keeping and breaking the blinding, and known only to him.

Patients and examiners will be masked to group membership; clinical examiners will be blinded to each other. The study analyst will be also blind to group membership. The analyst will receive the data by groups labeled as A and B. The blind will not be broken until after study completion. Complete root coverage (CRC) will be assumed as the main outcome at 6 months after treatment. At baseline and 6 months after surgery, the following clinical measurements will be also recorded on the mid-buccal point of exposed root surface: Gingival thickness (GT) will be determined using a stent at a mid-buccal location about 1 mm apical to the pocket depth (PD) level with a #15 endodontic reamer with a silicon disk stop. The soft tissue will be gently pierced at a 90° angle, until hard tissue will be felt. Once the silicon disk will be in contact with the soft tissue surface, it will be fixed by a drop of cyanoacrylate adhesive. After the careful removal of the reamer, the distance between the reamer tip and the stop will be measured with a calliper accurate to the nearest 0.1 mm. The other measurements will be taken with a periodontal probe and will be recorded to the nearest millimetre as follows: Gingival recession (GR) will be measured as the distance from the cement-enamel junction (CEJ) to the mid-buccal point of the gingival margin. PD and Clinical attachment level (CAL) will be measured as the distance between the bottom of the pocket and the gingival margin and CEJ, respectively. Keratinized tissue (KT) will be recorded from the mid-buccal point of the gingival margin to the mucogingival junction. Root coverage esthetic score (RES) (Cairo et al., 2009) will be used for assessing aesthetic outcomes of root coverage procedures. PROMs will also be evaluated. The degree of general discomfort (D) experienced will be assessed on a VAS scale (0-10). Patient-reported aesthetic satisfaction (PRES) at T1 will also be quantified on a VAS scale (0-10). Overall treatment satisfaction (OTS) at T1 will be assessed by asking each patient if they would undergo surgery again (yes/no). Thirty ml of blood samples will be collected in 10-ml tubes without anticoagulant and promptly centrifuged at 3,000 revolutions per minute for 10 minutes. The L-PRF membranes will be realized by a standardized compression of the clot for 120 seconds with 130 grams; the membranes will be put one on each other till obtaining a resultant membrane of the desired thickness: 1 or 2 mm. Exposed and intrasulcular root surface will be accurately scaled using curettes. A coronally advanced flap technique (CAF) will be used to treat the recession defect. The ﬂap will be elevated as follows: an intrasulcular incision will be performed around the selected tooth, the incision moves on contiguous papillae area, avoiding the gingival margin of adjacent teeth. From each side, from coronal to apical, an oblique incision will be carried out. A split-full-split dissection will be undertaken until the CEJ could be passively cover by the flap. Both papillae will be de-epithelialized. The 1 mm L-PRF membrane will be be placed over the exposed root surface of the CAF+ L-PRF 1mm group and the 2 mm L-PRF membrane in the CAF+ L-PRF 2 mm group. The gingival defect will be fully lined by grafts that mildly cover the neighbouring sub-papillae areas. In each group, ﬂap will be coronally positioned and sutured over the enamel in a tension-free position.

All patients will receive 2 g/day amoxicillin+clavulanic acid for 6 days for post-operative infection prevention; 400 mg of oral ibuprofen, twice daily, will control the pain; 0.12% chlorhexidine rinses, twice daily for 3 weeks, will be prescribe to the patients. Sutures will be removed after 14 days. Only 2-4 weeks after sutures removal, respectively, cautious brushing by a soft toothbrush and interdental brushing will be recommend; meantime, the patients use a 1% chlorhexidine gel twice daily. Weekly supra-gingival professional hygiene and motivational reinforcement will be administer to the patients for 6 weeks.