Putty form graft materials may have additional favourable effects when compared with particulate ones in periodontal bone defects. The purpose of this study was to assess clinical and also radiographic changes following application of (i) putty form demineralized bone matrix (DBM), (ii) particulate form DBM and (iii) open flap debridement (control), using modified curtain suturing technique in the treatment of interproximal suprabony (horizontal) defects. Twenty-five chronic periodontitis patients with 125 sites (radiologically 4 mm horizontal bone defect) were selected to participate in this triple-blind, split mouth, randomized, controlled clinical trial. Putty and particulate form DBM grafts were placed at experimental sites. Clinical measurements included probing depth (PD), relative attachment level (RAL), gingival recession and bone probing depth (BPD) were made at baseline and repeated 12 months after the operations. Standardized digital radiographs were also taken to measure radiographic bone level (RBL) at baseline and 12 months later to be compared in a software. Probing depth reductions and RAL gains were significantly improved in all treatment groups (P < 0.001). No significant differences in soft tissue parameters were found among three groups (P > 0.05). Bone probing depth measurements indicated comparable significant bone gain in graft applied groups (P < 0.01) and a significant bone resorption in open flap debridement group (P < 0.01). Radiographic evaluation did not show any significant bone gain or resorption in all treatment groups (P > 0.05). The results of this study indicate that either putty or particulate DBM demonstrates similar enhancements in soft and hard tissue parameters. Applying putty or particulate form DBM results with slight bone formation when compared with open flap debridement in horizontal bone defects at 1-year post-operative examination according to BPD measurements.