The study is a prospective, controlled, mono-center, randomized, clinical trial, that is open to the operator, blinded to the examiner. It will be conducted in a parallel group design. Participants who have at least 1 intra-bony periodontal defect will receive regenerative surgery at baseline with the randomly selected devices. A newly developed synthetically manufactured bone grafting material made of hydroxyapatite (Ostim) will be the product under investigation. An enamel matrix protein derivative (Emdogain) will act as control device. Both materials will be applied in intra-bony defects during periodontal flap surgery. Follow-ups will take place at 7 and 14 days post surgery, and at 3, 6, 9, and 12 months.