20 subjects presenting with horizontal mandibular ridge width less than 5 mm were selected and randomly divided two groups (10 in each group). the first group received interpositional block grafts (harvested from the chin and ramus) covered with Platelet-rich fibrin membrane. the second group received onlay block grafts (harvested from the chin and ramus) and covered with Platelet-rich fibrin membrane. the grafts are left for 4 months. the alveolar ridge width dimensions is then measured using radiographic analysis using cone-beam computed tomography scans