The present study is designed as a single-centre, parallel group, randomized, controlled clinical trial comparing the efficacy of EPP with or without biomaterials. Each patient will contribute with a single intrabony defect. Three months after completion of initial periodontal therapy, all the experimental sites will be accessed with the "EPP" technique (Aslan et al., 2017a) and carefully debrided. EDTA gel will be applied on the instrumented root surfaces. A combination of EMD and deproteinized bovine-derived bone substitute will be applied in the test group (EPP EMD + BS), while the control group (EPP) will not receive any regenerative biomaterial. Patients will be enrolled in a stringent maintenance programme with recalls on a weekly basis for the first month and then monthly controls for professional tooth cleaning up to 1 year. Clinical parameters will be recorded immediately before regenerative surgery (baseline) and 12 months after the regenerative periodontal surgery.