The present clinical trial included 20 patients (11 females and 9 males, aged 36 to 56 years) suffering from moderate or advanced chronic periodontitis. Subjects were recruited from the outpatient clinic, Department of Oral Medicine and Periodontology, Faculty of Dentistry, Cairo University. This clinical trial was meant to assess clinically and radiographically the possible predictable results regarding the use of nanocrystalline hydroxyapatite bone graft substitute together with open flap debridement versus open flap debridement alone in the treatment of periodontal intrabony defects.

periodontal intrabony defects in patients with moderate or advanced chronic periodontitis were treated with open flap debridement only in the control group while open flap debridement and Nanocrystalline Hydroxyapatite bone graft substitute was performed for the intervention group. probing pocket depth, clinical attachment level, gingival index, plaque index, gingival recession and bone defect area were assessed at baseline and six months post surgically to evaluate the possible improvement in the clinical and radiographic outcomes.

Inclusion Criteria:

• systemically healthy patients
• diagnosed with moderate to advanced chronic periodontitis
• periodontal defects with at least one site with probing pocket depth (PPD) ≥ 5mm, clinical attachment loss (CAL) ≥ 4mm and two or three-walled intra-bony defects ≥ 3mm
• evidence of intrabony defects using periapical radiographs

Exclusion Criteria:

• teeth with suprabony defects or 1-wall intrabony defects
• pregnant or lactating women
• patients taking any medication 3 months prior to the study
• patients receiving any periodontal treatment 6 months prior to study initiation
• former or current smokers.