Evaluation of bone contact area and intercondylar distance changes in orthognathic surgery - a comparison between BSSO and HSSO technique depending on mandibular displacement extent.

Objectives: The present study aims to assess the impact of bilateral and high oblique sagittal split osteotomy (BSSO/HSSO), as well as displacement distances and directions on the expected and achievable bone contact area (BCA) and changes in the intercondylar distance (ICD). The primary question addressed is whether mandibular splitting through BSSO results in a greater BCA and/or ICD when compared to splitting through HSSO.

Materials And Methods: Totally 80 mandibular displacements were performed on 20 fresh cadavers, for each subject, four splints were produces to facilitate mandibular advancement as well as setbacks of 4 and 8 mm. Pre- and postoperative CBCT scans were performed to plan the surgical procedures and to analyze the expected and achieved BCA and ICD.

Results: Regarding the maximum mandibular displacement, the expected BCA for HSSO/BSSO were 352.58 ± 96.55mm and 1164.00 ± 295.50mm, respectively, after advancement and 349.11 ± 98.42mm and 1344.70 ± 287.23mm, respectively, after setback. The achieved BCA for HSSO/BSSO were 229.37 ± 75.90mm and 391.38 ± 189.01mm, respectively, after advancement and 278.03 ± 97.65mm and 413.52 ± 169.52 mm, respectively after setback. The expected ICD for HSSO/BSSO were 4.51 ± 0.73 mm and 3.25 ± 1.17 mm after advancement and - 5.76 ± 1.07 mm and - 4.28 ± 1.58 mm after setback. The achieved ICD for HSSO/BSSO were 2.07 ± 2.9 mm and 1.7 ± 0.60 mm after advancement and - 2.57 ± 2.78 mm and - 1.28 ± 0.84 mm after setback. Significant differences between the BCA after HSSO and BSSO were at each displacement (p < 0.001), except for the achieved BCA after 8-mm setback and advancement (p ≥ 0.266). No significant differences were observed regarding ICD, except for the expected ICD after 8-mm setback and advancement (p ≤ 0.037).

Conclusions: Compared to the virtual planning, the predictability regarding BCA and ICD was limited. ICD showed smaller clinical changes, BCA decreased significantly in the BSSO group.

Clinical Relevance: BCA and ICD might have been less important in choosing the suitable split technique. in orthognathic surgery.