This study was conducted on 48 patients over 18 years of age (average age of 38 years). The patients required single-rooted incisor/premolar teeth extraction with a hopeless prognosis; for whom, socket preservation with PRF or FDBA was later performed. The reasons for tooth extraction included root fracture, failed root canal therapy, and extensive non-restorable caries. The ethics and study design was approved the Research Ethics Committee of Tehran University of Medical Sciences (IR.TUMS.DENTISTRY.REC.1396.2610) and conducted in accordance with the Declaration of Helsinki. All patients signed an informed consent prior to enrollment. They were free to leave the study at any time and ensured about the confidentiality of their information. The exclusion criteria included a history of systemic disease and head/neck radiotherapy, use of drugs affecting bone metabolism, smoking more than 10 cigarettes per day, the presence of significant periapical or periodontal lesions around the respective teeth, and the presence of dehiscence or fenestration larger than 3mm in the buccal bone plate. After extraction of the teeth, the patients underwent socket preservation with the use of PRF or FDBA. 4 months later, they received a Zimmer ScrewVent bone-level implant (Zimmer, Biomet, USA) which was left in place for 2 to 4 month (mandible and maxilla respectively) to achieve proper osseointegration. All implants were successfully osseointegrated. 10 patients were excluded during the study due to poor cooperation in the follow-up period. Eventually, 38 patients including 23 females and 15 males were subjected to hard and soft tissue assessments at 6 and 12 months, postoperatively. Patients in the PRF group included 9 males and 9 females (a total of 18) with a mean age of 30.81 years (ranging from 21 to 50 years). Patients in the FDBA group included 6 males and 14 females (a total of 20) with a mean age of 37.25 years (ranging from 22 to 50 years).

In second-stage surgery, a full-thickness flap was elevated and a gingival former (Zimmer, Biomet, USA) matching the fixture size placed. Soft tissue healing around the gingival former was allowed for 3 weeks and then a fixture level impression made using the closed-tray impression technique by additional silicone (Panasil, Kettenbach GmbH \& Co. KG, Eschenburg). The master cast was poured with G-mask SnowRock (Velmix; MungyoGroup, Korea) and Moldano dental stone (Tara, Iran). All selected abutments were straight, with a 0.5 mm gingival height. If the gingival height around an implant was variable, the higher value was chosen and other surfaces of the abutment were prepared such that the final finish line was positioned 0.5 mm subgingivally. After abutment preparation, a metal framework was waxed-up for a cement-retained metal-ceramic crown using resin pattern (GC Corporation, USA). The framework was then cast (Wirobond® C, Bego, USA) and tried in the second session. Vita Classic Shade Guide (Vitapan, Germany) was used to select the tooth shade. Porcelain adjustments (VITA VM ceramic, VITA Zahnfabrik, Germany) including the contacts, occlusion, contour and the esthetic appearance of the crown was performed at the third session. The crowns were then glazed. In the fourth prosthetic session, the abutments were tighten to 25 N.Cm final torque and sealed with a Teflon band. The glazed crown was cemented with temporary cement (TempBond, Kerr) and excess cement thoroughly removed. Complete seating of the crown and excess cement removal were ensured in the first radiograph.

To assess the hard tissue stability around each implant, a digital radiograph (Digora Optime, Acteon, India) was obtained with a size 2 sensor using a film holder (Kerr). All baseline and follow-up radiographs were parallel and exposure settings were the same for each patient in the baseline and follow-up radiographs. Using Scanora software (SCANORA lite, Soredex, Helsinki, Finland), the distance from the crestal bone-fixture interface to the abutment-crown interface (crown margin) was measured at the mesial and distal surfaces of the implant at 0, 6 and 12 months after implant placement (Fig1).These measurements were repeated 3 times at the mesial and 3 times at the distal surfaces for each patient and the mean values reported to minimize the errors. To assess soft tissue changes, clinical gingival parameters including the gingival recession (defined as the change in the distance from the gingival margin to the crown margin compared with time 0), the papilla index (distance from the tip of the papilla to the crown margin in the mesial and distal surfaces) (Fig2), and bleeding on probing (BOP) at the mesiobuccal and distobuccal points were measured at 0, 6 and 12 months, postoperatively.

Data were analyzed using SPSS version 22. Qualitative variables were compared using Fisher's exact test while quantitative variables were compared using unpaired student's t-test. The level of significance was set at 0.05.