The aim of this randomized clinical trial is to evaluate the potential benefit of the use of a bone substitute material in the treatment of furcation degree II-involved molars. The main question it aims to answer is: What is the benefit of the adjunctive use of a bone substitute material in the surgical treatment of furcation degree II-involved molars when compared to open-flap debridement alone? 200 patients with ≥1 molar presenting with a furcation defect degree II will be included and randomized to either control (open-flap debridement) or test treatment (open-flap debridement + bone substitute material). The primary outcome of the study is furcation closure defined as absence of clinically detectable furcation involvement degree \>I. Secondary outcomes include changes in bleeding on probing, probing depth, vertical and horizontal attachment levels, soft tissue level, marginal bone level, need for surgical retreatment, tooth loss, patient-reported outcomes and adverse events. A composite outcome based on furcation closure (degree ≤I) in combination with shallow probing depth (≤5 mm) and absence of bleeding on probing will also be evaluated.