Objective: To compare the effect of guided tissue regeneration (GTR) + concentrated growth factors (CGF) + bone graft and CGF + bone graft in the treat of II° furcations of human mandibular molars. Methods: At least thirty II°furcation involvements in mandibular molars will be included and randomly divided into two groups. The experimental group will accept GTR + CGF + bone graft therapy, and the control group will accept CGF + bone graft therapy. The clinical examination and cone beam computed tomography (CBCT) will be performed at baseline and 1 year post-surgery.