This case report describes a patient with severe (11-mm) mandibular anterior crowding who received periodontally accelerated osteogenic orthodontics (PAOO) nonextraction treatment, showing 5-year follow-up. A 15-year-old female presented with severe dental crowding, Angle Class I skeletal and molar relationships and a Class II canine relationship, and excessive overjet and overbite. Following fixed-appliance placement (0.022-inch, MBT prescription), full-thickness periosteal flaps beyond the tooth apices were raised bilaterally from the second molars in both arches, and selective decortication of cortical bone was performed on the facial and lingual sides using a surgical tool. Bone grafting material, comprised of a mixture of demineralized freeze-dried bone allograft (DFDBA) and bovine bone (Bio Oss, Geistlich), was placed at the corticotomy sites. The patient was seen every 2 weeks after the surgery for orthodontic adjustments; the total active orthodontic treatment time was 9 months. Limits of tooth movement (the scope of treatment) were increased by the bone-graft augmentation. At the 5-year follow-up, cephalometric comparisons to baseline conditions showed dramatic incisor changes and stable dentoalveolar effects. This case demonstrates the efficacy of PAOO as a useful adjunct orthodontic strategy for adult patients who require treatment of severe crowding, ie, treatment that would be considered unreasonable if conventional orthodontics were employed. When conventional orthodontics cannot achieve the treatment goal and orthognathic surgery is not feasible, PAOO expands the scope of conventional orthodontic treatment in the adult 2-fold to 3-fold in most spatial dimensions.