Treatment of intrabony defects using guided tissue regeneration and autogenous spongiosa alone or combined with hydroxyapatite/beta-tricalcium phosphate bone substitute or bovine-derived xeno-graft - Zafiropoulos, G G; Hoffmann, O; Kasaj, A; Willershausen, B; Weiss, O; van Dyke, T E (J Periodontol, 2007)