The primary outcome of the present study will be assess the percentage of pocket closure and the secondary aim to evaluate the clinical performance in terms of clinical attachment level (CAL) gain, probing pocket depth (PPD) reduction and gingival recession (REC) after the use of cavitron ultrasonic surgical aspirator (CUSA) in deep infrabony defects.

Patients who were previously treated with active periodontal therapy followed by one year of supportive periodontal therapy (at least three sessions) will be additionally treated by the aid of CUSA. Subjects will be reviewed at 7 days, 15 days, 1 month, 3 months and 6 months. These sessions will include supra-gingival professional mechanical plaque removal (PMPR) through the use of erythritol powder plus 14 μm. Clinical measurements of the defects and X-ray with bite block will be taken at baseline and 3 and 6 months.

This will be a Phase 2 non-controlled clinical trial performed on patients with infrabony defects to test whether the employment of CUSA for treating periodontal patients:

1. Provides benefits in terms of a PPD reduction and CAL gain
2. Is comfortable for patients and operators; and is free from adverse events

All subjects included in the study will be consecutive periodontal patients attending a private clinic in Settimo Milanese (Milan, Italy) who will be treated by two operators with similar experience in non surgical produce who performed a specific training for CUSA on a periodontal model.

The clinical procedure will be always performed in a single session. Before intervention, all cases will receive local anaesthesia with 1:100.000 mepivacaine.

All residual pockets ≥ 5 mm will be treated with

1. Ultrasonic debridement: to minimize trauma to the soft tissues, the investigators used piezo-electric devices with specific thin and delicate tips (E.M.S. Electro Medi- cal Systems S.A. Chemin de la Vuarpillière, 31 1260, Lyon Swizerland).

2. Flapless treatment: according to the anatomy of the osseous sites, the sonotrode (Sonocare 300 by Söring GmbH, Justus-von-Liebig-Ring 2 -25451 Quickborn Germany) will be inserted both intrasulcularly and trans gingivally (smallest tip is 0,8 mm); intrasulcularly in the cases of three wall defects, and trans gingivally in cases of one to two wall defects . The stack of piezo-electric quartzes transforms the electrical energy from the generator into a longitudinal, mechanical vibration of the sonotrode tip. When the tip of the sonotrode approaches the tissue, the ultrasonic energy, as a result of the high force of acceleration and cavitation effect, separates cells from the conglomerate of tissues (fragmentation). The fragmented tissue can be aspirated as a semiliquid substance through the sonotrode hole, freeing the defect from the formation of a stable blood clot.

   The end point will be achieving a condition in which the infrabony defect is free from the granulation tissue.

3. After CUSA treatment, to stimulate the formation of a stable blood clot, the use of any sub gingival rinses will be avoided.

No medications will be prescribed advising the patients to use painkillers (NSAIDs) if they experience postoperative pain.

Subjects will be reviewed at 7 days, 15 days, 1 month, 3 months and 6 months. These sessions will include supra-gingival professional mechanical plaque removal (PMPR) through the use of erythritol powder plus 14 μm (AIR-FLOW® MASTER -EMS).

Clinical measurements of the defects and X-ray with bite block will be taken at baseline and 3 and 6 months.

Outcomes :

• Pocket Closure proportion (PPD < 5 mm);
• Probing depth (PPD) reduction;
• CAL gain; and
• Gingival recession.
• Comfort and acceptability of the patient during and after the procedure, as measured by interviews, use of painkillers in the following three days and the visual analogue scale (VAS) after one week
• Comfort and convenience of the operator during the procedure, as measured by interviews at the end of the procedure; and adverse events

Continuous variables will be expressed as the mean ± standard deviation (SD). Dichotomous data will be expressed as a percentage. The comparison between baseline and 6 months after flapless treatment will be performed by applying a Wilcoxon signed ranked test.

Inclusion Criteria:

1. Having received a diagnosis of chronic periodontitis (Armitage 1999)
2. Being treated by full mouth debridement, and supportive periodontal treatment (SPT) in the last year (at least three sessions) by one of the authors
3. Having at least one residual pocket ≥ 5 mm with and intra bony component at least ≥ 2 mm

Exclusion Criteria:

1. Smoking more than ten cigarettes per day
2. Pregnancy
3. Irregular compliance during SPT in the last year; and systemic conditions or therapies known to affect the healing potential of periodontal tissues (e.g., uncontrolled diabetes, oncological conditions, immunosuppressant drugs).