Abstract : Reconstruction of alveolar defects after tooth loss is one of the biggest challenges in implant dentistry, to augment bone defects grafts of various origins have been used, the mode of graft integration depends primarily on its origin and composition. Among graft material used is the autogenous bone, which considered the gold standard for augmentation due its osteoinductive, osteogenic, osteoconductive with significant regenerative capacity over all other grafts. Intraoral sources of autogenous bone are considered the preferred donor site, due to proximity of donor and recipient sites, convenient surgical access, low morbidity, and elimination of a hospital stay. Severe alveolar defects necessitate using sufficient quantity of structurally resistant bone block for reconstructions, cortico-cancellous bone block grafts suitable for two- or three- dimensional reconstruction of these defects can be harvested only from mandibular symphysis and retromolar area. Radiographic evaluation of the outcomes of horizontal defect reconstruction with autogenous bone block harvested from retromolar area in terms of amount of horizontal bone gain and graft density four months postoperatively. This study included 10 patients for reconstruction of horizontal ridge defect using autogenous bone block harvested from retromolar region, the patients were treated at the oral and maxillofacial surgery unit of Al-Yarmouk teaching hospital and private clinic during the period from January 2020 to October 2021, the age of patients ranged from 20 to 53 years old, all patients were medically fit to undergo a bone grafting procedure. Cone Beam Computed Tomography was used for assessment of bone density and horizontal bone width pre-operatively and 10 days, 4 months post-operatively. Post-operative complications were assessed and recorded during the follow-up period. In this study, the females’ percentage was higher than males (70% versus 30%). The mean of the pre-operative width of alveolar defect was (2.54 ± 0.42) mm, after 4 months the mean of bone width gain was (4.480 ± 0.823) mm. The density of the pre-augmentation site measured with a mean of (784.8 ± 183.8) HU, then after 4 months of bone grafting procedure the density of grafted area also measured, the mean was (666.8 ± 106.4) HU. All patients developed swelling post-operatively and resolved gradually, 90% of patients complained of pain during the first week postoperatively, while only (10%) suffered from sensory disturbance for 2 weeks after the operation. Mandibular ramal bone block used according to the split block technique is a predictable method for augmentation of sever horizontal defects, autogenous bone grafts remain the gold standard of grafting materials, Cone Beam Computed Tomography is recommended, as these scans provide precise information about the thickness of bone and position of inferior alveolar nerve, the use of piezo surgery unit led to precise and clean harvest graft with minimal wastage of bone, and the overall morbidity of mandibular block for ridge augmentation is minimal.