This will be a spontaneous, postmarketing trial with a medical device (MD), split-mouth, nationwide multicenter study (coordinator center: Periodontal Unit, Dental Clinic, DIBINEM, Bologna University, Italy, with satellite center involved), single-blind (examiner), randomized controlled trial comparing, at different time points, the clinical efficacy of PX-Gel-a thermosensitive hyaluronic acid-octenidine gel-in enhancing gingival healing of periodontal pockets when used as an adjunct to scaling and root planing (test group) versus conventional SRP (control group). SRP represents the gold standard for non-surgical treatment of periodontitis and it is the standard of care.

Each patient will contribute with at least 4 sites with a PD more than 5 mm and positive BOP in 2 contralateral quadrants. The sites will be randomly assigned to one of the two treatment regimens, using a predetermined computer- generated randomization scheme, regarding left or right side) to receive the test treatment (SRP + PX-gel) or to serve as SRP controls.

Allocation concealment will be performed by opaque sealed envelopes, sequentially numbered. The allocation sequence will be generated by means of a computer-generated random list (https ://www.sealedenve lope.com/simple-randomiser/ v1/) and a different subject (not involved in the treatment) will be instructed to assign a sealed envelope containing the treatments of each site (SRP+ PX-Gel or SRP). The opaque sealed envelope will be opened immediately after the end of the SRP session.

Blinding of independent examiner will be maintained through-out all study period.

The patients will not be informed of the locations where the treatment gel will be applied.

All adult subjects referred to the Periodontal Unit and involved satellite center for periodontal treatment will be screened and enrolled in the study according to the following inclusion/exclusion criteria:

• Patients agreeing to participate in the study
• Age 18 years or older
• ≥ 20 existing teeth (wisdom teeth excluded).
• Diagnosis of periodontitis stage II-III or IV (any grade) of periodontitis
• Each participant should have 2 or more contralateral quadrants with a minimum of 4 qualifying pockets of ≥ 5 mm that bled on probing
• Full-mouth parallel periapical X-rays demonstrating bone loss (standard of care)