The current most common technique for mandibular split is the sagittal split osteotomy described by Obwegeser and modified by Dalpont and Epker. Several studies have shown a lower face enlargement while employing these techniques. The supra-basilar sagittal split osteotomy described in 2017 seems to be an interesting alternative as mandibular angles remain in continuity with the internal valve. The aim of this study was to evaluate lower face enlargement by comparing two techniques: sagittal split osteotomy and supra-basilar sagittal split.

Cephalograms were analyzed before and after surgery. Bigonial distances (BGD) were measured in frontal cephalograms, ramus length and distances between upper and lower incisors on lateral cephalogram. Control of those measures was also performed by measuring the Nasion-Anterior Clinoid distance and intercanthal distance to assess the comparability and error rate. Finally, a comparison of cephalograms before and after surgery to assess bigonial enlargement, ramus elongation and advancement was performed.

Out of the 69 patients, 18 had a Bilateral Sagittal Split (BSSO) and 52 had a Supra-Basilar Sagittal Split (SBSSO). The error rate and patients’ characteristics were the same in the two groups. A statistically significant widening of the bigonial distance with the BSSO in comparison with the SBSSO was found (BGD difference: 5.82 mm (BSSO) vs - 1.47 mm (SBSSO), p < 0,001). A greater ramus elongation with the SBSSO was found (ramus elongation: 1.12 mm (BSSO) vs 5.1 mm (SBSSO)). This study has shown that the supra-basilar sagittal split is an interesting way to avoid the widening of the mandibular angles.