This study will evaluate changes in Surfactant Protein D (SP-D) levels in gingival crevicular fluid (GCF) of patients with periodontitis before and after minimally invasive non-surgical periodontal therapy (MINST).

Participants diagnosed with stage II or III periodontitis will receive minimally invasive non-surgical periodontal treatment. GCF samples will be collected at baseline and 6 months after treatment, and SP-D levels will be measured using enzyme-linked immunosorbent assay (ELISA).

The study will also assess clinical periodontal outcomes, including full-mouth plaque score, full-mouth bleeding score, probing pocket depth, clinical attachment level, gingival recession, and patient satisfaction. Each participant will serve as their own control by comparing baseline values with 6-month post-treatment values.

Periodontitis is a chronic multifactorial inflammatory disease characterized by progressive destruction of the supporting periodontal tissues. Conventional clinical parameters, such as probing pocket depth, bleeding on probing, and clinical attachment level, are useful for diagnosis and follow-up but may reflect tissue destruction after it has already occurred. Therefore, biomarkers that reflect the biological inflammatory status of periodontal tissues may improve monitoring of disease activity and treatment response.

Surfactant Protein D (SP-D) is an innate immune molecule involved in host defense and modulation of inflammation. It has been detected in oral fluids, including gingival crevicular fluid, and may be associated with periodontal inflammation. This study aims to evaluate whether SP-D levels in GCF change after minimally invasive non-surgical periodontal therapy in patients with periodontitis.

This is a single-group before-and-after interventional clinical study. Eligible participants with stage II or III periodontitis will be recruited from the outpatient periodontal clinics of the Faculty of Dentistry, Cairo University. At baseline, periodontal clinical parameters will be recorded, including full-mouth plaque score, full-mouth bleeding score, probing pocket depth, clinical attachment level, and gingival recession. GCF samples will be collected from selected periodontal sites using sterile paper strips and stored until biochemical analysis.

All participants will receive minimally invasive non-surgical periodontal therapy, including oral hygiene instructions, supragingival plaque control, and subgingival instrumentation using minimally invasive techniques. Treatment will be performed using fine periodontal instruments, thin ultrasonic tips, magnification when available, and local anesthesia when needed to improve patient comfort and minimize tissue trauma.

After 6 months, participants will be recalled for clinical re-evaluation and collection of post-treatment GCF samples from the same sites. SP-D levels will be measured using ELISA. The primary outcome will be the change in SP-D level from baseline to 6 months after treatment. Secondary outcomes will include changes in plaque score, bleeding score, probing pocket depth, clinical attachment level, gingival recession, and patient satisfaction.

Inclusion Criteria:

• Male and female participants aged 18 years or older.
• Diagnosis of periodontitis, classified as stage II or stage III according to the 2018 classification system.
• Presence of at least one tooth with probing pocket depth (PPD) of 5 mm or more, clinical attachment loss (CAL), and radiographic evidence of bone loss.
• Presence of at least one intrabony defect with a radiographic intrabony component measuring 3 mm or more.

Exclusion Criteria:

• Current smokers or individuals with a history of smoking within the past year.
• Pregnant or lactating women.
• Use of systemic antibiotics or anti-inflammatory medications within the last 3 months.
• Known allergy to any materials or agents used during periodontal therapy.

Laboratory personnel measuring SP-D levels using ELISA will be blinded to the timing of sample collection, whether baseline or 6 months after treatment. Data analysts will also be blinded to the timing of sample collection. Participants and clinicians cannot be blinded because of the nature of the periodontal intervention.