To investigate the effect of lower border osteotomy on the lingual split pattern and IAN in BSSO procedures.

The study comprised 32 patients (64 operated sides) who underwent bilateral sagittal split osteotomy (BSSO) due to dentofacial abnormalities between the periods of April 2021 and April 2022. In the mandible, 32 sides (the conventional group) received standard BSSO surgery, while 32 sides (the modified group) additionally received lower border osteotomy. Data regarding the split difficulty of the mandibular in BSSO surgery and the recovery status of the inferior alveolar nerve (IAN) one year after surgery were obtained and evaluated from patient records. The fracture line was radiographically evaluated for the lingual split pattern following surgery.

A statistically significant difference was observed in favor of the modified group when the mandibular split difficulty of the groups was compared (p = 0.032). The split time of the modified group was found to be statistically shorter than the conventional group (p ≤ 0.001). The mean numbness level of the modified group one year after surgery was statistically significantly lower than that of the conventional group (p = 0.019). Although there was no statistically significant difference between the two groups in terms of lingual fracture pattern, the rate of type 1 (87.5 %) fracture was higher in the modified group compared to the other group (68.8 %) (p = 0.089).

The lower border osteotomy performed in addition to the conventional BSSO surgery allows the split procedure easier and in a shorter time. The modification resulted in an increased incidence of type 1 lingual fracture pattern in the mandible. The neurosensory recovery capacity of the IAN in the postoperative period is higher in areas where lower-border osteotomies are performed.