In this study, the effectiveness of a corticocancellous block allograft for restoring alveolar ridge defects in preparation for the placement of dental implants was assessed. Significant ridge defects in four partially edentulous patients were reconstructed using an irradiated corticocancellous allogeneic block soaked in platelet-rich plasma, which was also covered with a resorbable collagen membrane. After 5 or 6 months, the sites were reentered and a trephine bone core specimen was obtained from each augmented site for histologic, histomorphometric, and immunohistochemical assessment. In all four cases, histologic evaluation of the augmented site showed areas of new vital bone formation around the graft material (mean newly formed bone fraction, 23.7%; mean total mineralized tissue fraction, 40.1%), in which osteocytes were frequently observed within the lacunae. Immunohistochemical analysis showed the presence of biomarkers commonly related to active bone formation (alkaline phosphatase, osteocalcin, and bone morphogenetic protein-2), confirming that the biochemical environment was conducive to new bone formation. The findings of this study demonstrate that the use of allogeneic block grafts for restoring alveolar ridge defects prior to the placement of dental implants may be an effective and advantageous alternative to autograft procedures.