Do cortical and medullary bone volume, and retromolar and ramus thickness, influence the sagittal split pattern? A retrospective analysis.

Sagittal split osteotomy (SSO) is a well-established technique for mandibular repositioning, although unfavourable split patterns remain a relevant intraoperative concern. This retrospective study evaluated anatomical factors influencing split morphology, including cortical and medullary bone volumes and mandibular ramus thickness. Pre- and postoperative imaging from 94 SSOs were analysed, and split patterns were classified using the adapted Plooij Lingual Split Scale (LSS). Associations were assessed with the Kruskal-Wallis test, with the Wilcoxon rank sum and Fisher's exact tests used to compare Angle malocclusion classes. Ideal splits (LSS 1) occurred in 68.1% of cases, followed by splits over the canal (LSS 3) in 22.3%, posterior ramus border splits (LSS 2) in 5.3%, and bad splits (LSS 4) in 4.3%. LSS 1 cases showed significantly greater cortical bone volume (P = 0.005) and increased ramus thickness at all measured levels (P < 0.001, P < 0.001, P = 0.0039). Angle class II patients had greater ramus thickness (P = 0.045) and lower medullary bone volume than class III patients. Greater bone volume and ramus thickness were associated with more favourable split outcomes. Further prospective studies are needed to confirm these findings.