Purpose: Ridge expansion is used to widen narrow ridges with adequate height for implant placement. This human case series presents the clinical and histologic results of delayed expansion of mandibles by ultrasonic surgery. Materials and Methods: Patients with residual alveolar ridge width between 2.3 and 4.1 mm in the coronal area of the posterior mandible were included in the study. First, four linear corticotomies were carried out by ultrasonic surgical device. Four weeks later, adequate bone expansion with a combination of scalpels, thin chisels, and threaded osteotomes that did not compromise cortical vascularization was performed, and two implants per ridge were inserted. Any gaps were filled with corticospongious porcine biomaterial. Three months after implant placement, healing caps were inserted, and bone cores were harvested from the regenerated areas for histologic analysis. Crestal width was recorded at each surgery. Results: The postoperative course was uneventful in all 32 patients (64 implants) who took part in the study, and the implant success rate was 96.88% at 3 months. The mean increase in ridge width was 5.17 ± 0.86 mm. The histologic specimens showed a mixture of new bone and particles of biomaterial, as well as newly formed bone. Histomorphometry demonstrated that 64% ± 3.1% of the specimen was composed of newly formed bone, 8% ± 0.8% was made up of marrow spaces, and 27% ± 2.6% comprised the residual grafted biomaterial. Conclusion: This study showed that mandibular ridge expansion using a delayed splitcrest technique by means of ultrasonic surgery and association with biomaterial led to good horizontal bone gain, with no fractures of the buccal plate, and a high implant success rate. The histologic specimens showed newly formed bone and good integration of the biomaterial. Keywords: alveolar bone loss, alveolar ridge augmentation, bone regeneration, bone resorption, piezosurgery