Objective: To evaluate mandibular irregularity index stability following orthodontic treatment facilitated by alveolar corticotomy and augmentation bone grafting (Cort+). Materials and Methods: The irregularity index of 121 orthodontically treated and 15 untreated patient study casts was analyzed at 5 years and 10 years. Results: Cort+ resulted in significantly lower mandibular irregularity index scores at both 5 years (1.5 mm vs 4.2 mm, P , .000) and 10 years (2.1 mm vs 4.1 mm, P , .000) compared with conventionally treated patients. Conclusions: Unmatched samples advise caution with conclusions, but orthodontic therapy combined with Cort+ enhanced the stability of the postorthodontic mandibular irregularity index for at least 10 years in this preliminary study.