In 13 patients with advanced periodontitis 30 periodontal defects (8 intrabony, 21 class II, 1 class III furcation) were treated by conventional surgery (n = 5) or guided tissue regeneration (GTR) using expanded polytetrafluoroethylene (n = 14) or Polyglactin 910 barriers (n = 11). Presurgically (BL), 6, and 60 months postsurgically clinical parameters (GI, PlI, PD, CAL-V, CAL-H) and 24 standardized radiographs were obtained generating 48 pairs (24 BL/6 months; 24 BL/60 months). Using subtraction analysis, bony fill within the defects was assessed. Surgically at baseline and by sounding 60 months after surgery vertical (PBL-V) and horizontal (PBL-H) bone levels were measured. Statistically significant (P Schlagwörter: Furcation defects, intrabony defects, periodontal surgery, digital subtraction analysis, intrasurgical measurements