Background: The aim of this 5 year randomized controlled clinical trial was to evaluate the long-term results after GTR-therapy of infrabony defects using 2 bioabsorbable barriers (test: polydioxanon; control: polylactide ace-tyltributyl citrate).Methods: In 15 patients suffering from moderate to severe periodontitis 15 pairs of contralateral infrabony defects were treated. Within each patient one defect received a polydioxanon (test: T) and the other a polylactide acetyltributyl citrate (control: C) barrier by random assignment. At baseline, 12, and 60 ± 3 months after surgery clinical parameters and standardized radiographs were obtained. Vertical bone levels (PBL-V) were measured intrasurgically and 60 ± 3 months later by transgingival bone sounding. Results: 13 of 15 patients were available for the 60-months re examinations. Twelve and 60 ± 3 months after GTR therapy statistically significant (P 2 mm compared to the 12 months re examination. Twelve and 60 ± 3 months after surgery statistically significant (P Keywords: interproximal infrabony defects/therapy, guided tissue regeneration, membranes, artificial, membranes, barrier, bioabsorbable barriers, radiography, dental, randomized controlled clinical trial, long-term results