The extraction of deep impacted mandibular third molar may cause periodontal defects at the distal root of the second molar. The aim of this study was to evaluate the ability of platelet-rich fibrin (PRF) in preventing periodontal complications at the distal root of the second molar adjacent to the extracted third molar.

Eighteen young patients with bilateral impacted mandibular third molars will be selected. All 36 cases of impactions will be selected for a split mouth study and randomly treated by using 2 different therapeutic approaches, thereby yielding 2 different study groups, each of which is composed of 18 cases: in one side the post-extraction socket is left healing spontaneously, on the other side the socket is filled with PRF.

CAL at the distal surface of the lower second molar is chosen as primary outcome.

Criteria will be the presence of a pocket distal to the mandibular second molar with a probing depth >7 mm and a probing clinical attachment level >6mm.

This study was designed as a single-blind research since subjects will be unaware of their treatment allocation. A software will be used to produce a random sequence of 18 integer numbers without duplicates generated from atmospheric noise and concealed in closed envelopes by one of the investigators. At the time of the patient's first surgery, the envelope will be opened and patient allocated either to group 1 (PRF on the right side, spontaneous healing on the left side), for allocation numbers 1-9, or group 2 (spontaneous healing on the right side, PRF on the left side), for allocation numbers 10-18.

One clinician, not involved in patient treatment and not aware of what therapeutic approach used for the different sites of treatment, will perform all clinical measurements (PD, CAL, gingival recession, plaque index and gingival bleeding index) before and after 12 and 18 weeks of surgery.

Clinical and radiographical measurements will be recorded at 12 and 18 weeks after the surgery. The Student t test will be used to compare the differences between the 2 groups.

Inclusion criteria Patients of both genders and any race, between 18 and 35 year-old

• Periodontally health patients and treated periodontally compromised patients
• Enrollment on a regular supportive periodontal therapy (SPT) program.
• Full-mouth plaque score (FMPS)< 25% at baseline;
• Full-mouth bleeding score (FMBS)< 25% at baseline;
• Patients having bilateral mesioangular impacted mandibular third molars with the presence of a pocket distally to the mandibular second molar with a probing depth (PD) ≥7 mm
• Intact buccal and lingual cortical bone of the post-extraction site

Exclusion Criteria:

• General contra-indications for surgery (systemic disease, compromised immune system etc);
• Tobacco smoking
• Pregnancy and lactation
• Untreated periodontal conditions;
• Acute infection in the site of the extraction
• Patients taking any medications which might interfere with coagulation
• Platelet count < 150000/mm3

One clinician, not involved in patient treatment and not aware of what therapeutic approach was used for the different sites of treatment, performed all clinical measurements (PD, CAL, gingival recession, plaque index and gingival bleeding index) before and after 12 and 18 weeks of surgery.