This randomized controlled clinical trial aims to evaluate the effectiveness of using nano-hydroxyapatite (nHA) gel alongside a minimally invasive non-surgical technique (MINST) to treat deep intra-bony defects in patients with Stage III periodontitis. While MINST is an effective method for cleaning deep periodontal pockets without the need for traditional surgery, the addition of nHA may further enhance soft tissue healing, improve cellular interaction, and promote bone regeneration. Participants in the study will be randomly assigned to one of two groups. The test group will receive the MINST procedure combined with the application of nHA gel directly into the periodontal pocket, while the control group will receive the MINST procedure alone. The primary goal of the study is to measure the decrease in probing pocket depth over a 6-month follow-up period to determine if the adjunctive use of nHA provides superior clinical outcomes compared to non-surgical treatment alone.

Inclusion Criteria:

• Systemically healthy adults aged 18-65 years.
• No history of systemic diseases affecting periodontal status or bone metabolism (e.g., uncontrolled diabetes, osteoporosis).
• Diagnosed with Stage III periodontitis according to the 2018 classification of periodontal diseases (with interdental CAL ≥5 mm, probing depth ≥6 mm).
• Presence of at least one deep intra-bony defect (≥3 mm defect depth) in a single-rooted or multi-rooted tooth.
• Willingness to participate and sign informed consent.

Exclusion Criteria:

• Immunocompromised patients, uncontrolled diabetics (HbA1c ≥ 7.0%), or individuals with autoimmune disorders.
• History of malignancy or chemotherapy/radiation in the past year.
• Use of bisphosphonates, corticosteroids, immunosuppressive antibiotics or anti-inflammatory agents within 6 months before periodontal therapy.
• Smokers (≥ 10 cigarettes per day).
• Pregnant or breastfeeding women, confirmed via medical history and/or test.
• Receipt of periodontal surgery or nonsurgical treatment within the last 6 months.
• Teeth with peri-apical pathology, acute abscess, or grade III mobility.
• Multi-rooted teeth with class II and class III furcation defects.
• Third molars.