Patients with residual periodontal pockets following non-surgical periodontal therapy remain at risk for disease progression and may require further periodontal surgery. Repeated scaling and root planing (SRP) is commonly used for residual pockets; however, complete elimination of periodontal pathogens is often difficult to achieve. Ozone therapy has antimicrobial, anti-inflammatory, and wound-healing properties that may improve periodontal treatment outcomes.

The aim of this randomized controlled clinical trial is to clinically and microbiologically evaluate the adjunctive effects of gaseous ozone application during repeated SRP for residual periodontal pockets in patients undergoing periodontal maintenance therapy. Twenty-six patients diagnosed with stage III or IV periodontitis presenting with residual periodontal pockets ≥5 mm with bleeding on probing will be included. Residual pockets will be randomly assigned to either repeated SRP alone (control group) or repeated SRP combined with ozone application (test group).

Clinical periodontal parameters and microbiological findings will be evaluated at baseline, 3 months, and 6 months after treatment.

Periodontitis is a chronic multifactorial inflammatory disease associated with dysbiotic subgingival biofilm and progressive destruction of tooth-supporting tissues. Although scaling and root planing (SRP) represents the gold standard of non-surgical periodontal therapy, residual periodontal pockets may persist after treatment, especially in patients with stage III and IV periodontitis. Residual pockets ≥5 mm with bleeding on probing are associated with increased risk of disease recurrence and often require additional interventions.

Adjunctive therapeutic approaches have been proposed to improve outcomes of non-surgical periodontal treatment. Ozone therapy has attracted increasing interest in periodontology because of its antimicrobial, anti-inflammatory, antihypoxic, immunomodulatory, and wound-healing effects. However, evidence regarding the adjunctive use of ozone in residual periodontal pockets remains limited.

This study was designed as a split-mouth, randomized-controlled, double-blind clinical trial with a 6-month follow-up period. Twenty-six systemically healthy individuals diagnosed with stage III or IV periodontitis and undergoing periodontal maintenance therapy will be included. Patients presenting with residual periodontal pockets ≥5 mm with bleeding on probing following previous non-surgical periodontal treatment will be enrolled.

Residual periodontal pockets will be randomly assigned to one of the following groups:

Control group: repeated scaling and root planing alone Test group: repeated scaling and root planing combined with gaseous ozone application

Clinical periodontal measurements including plaque index (PI), gingival index (GI), bleeding on probing (BOP), probing depth (PD), recession depth (RD), and clinical attachment level (CAL) will be recorded using a standardized acrylic stent and a UNC-15 periodontal probe. Microbiological evaluation will be performed using the benzoyl-DL-arginine naphthylamide (BANA) enzymatic assay.

Ozone application will be performed using the OzoneDTA device with a periodontal probe tip according to the manufacturer's instructions. Clinical and microbiological evaluations will be performed at baseline, 3 months, and 6 months.

The primary objective of this study is to evaluate whether adjunctive ozone application improves clinical periodontal outcomes in residual periodontal pockets compared with repeated SRP alone.

Inclusion Criteria:

• Systemically healthy individuals
• Patients diagnosed with stage III or IV periodontitis
• Patients undergoing periodontal maintenance therapy
• Presence of at least two residual periodontal pockets ≥5 mm with bleeding on probing
• Presence of radiographic bone loss ≥3 mm
• Plaque Index (PI) <1 before treatment
• Ability and willingness to attend all follow-up visits
• Written informed consent obtained

Exclusion Criteria:

• Presence of systemic diseases affecting periodontal healing
• Pregnancy or lactation
• Tobacco or alcohol use
• Use of medications affecting periodontal tissues or wound healing
• Periodontal treatment within the previous 6 months
• Presence of carious lesions or periapical pathology on selected teeth
• Furcation involvement
• Tooth mobility ≥ degree 1
• Restorations on selected teeth

Individual participant data will not be publicly available due to privacy and confidentiality considerations.

Clinical and microbiological measurements were performed by a blinded examiner who was not involved in treatment procedures.