Are there risk factors for osseous mandibular inferior border defects after bilateral sagittal split osteotomy?

Is it necessary to use bone grafts to prevent defects at the lower border of the mandible after mandibular advancement?-a systematic review

INTRODUCTION

Defects in the lower border of the mandible may represent an aesthetic problem after mandibular advancement in orthognathic surgery. The use of bone grafts has been reported in the literature as a possibility to reduce these defects in the postoperative period.

OBJECTIVE

The objective of this systematic review is to answer the following research question: Is it necessary to use bone grafts to prevent defects at the lower border of the mandible after mandibular advancement?

METHODS

The literature search was conducted on MEDLINE via PubMed, Scopus, Central Cochrane, Embase, LILACS, and Sigle via Open Gray up until December 2020. Five studies were eligible for this systematic review, considering the previously established inclusion and exclusion criteria.

RESULTS

1340 mandibular osteotomies were evaluated, with a mean advance of 8 mm, being 510 with bone graft (42 defects), 528 without graft (329 defects), and 302 with an alternative technique (32 defects). Regarding the type of bone graft used, three articles used xenogenous or biomaterial grafts and two allogenous bone grafts. The results of the meta-analysis showed a reduction in the presence of defects in the bone graft group: OR 0.04, 95% CI = 0.01, 0.19; p = 0.0005, (I2 = 87%; p < 0.0001).

CONCLUSION

The use of bone grafts seems promising in reducing defects in the lower border of the mandible after mandibular advancement. New controlled prospective studies with a larger number of participants are needed to ensure the effectiveness of this procedure.

Risk factors for lower border notching after bilateral mandibular sagittal ramus advancement: three-dimensional evaluation

Bilateral sagittal split osteotomy (BSSO) mandibular advancement can cause mandibular lower border notching (MLBN). The objective of this study was to calculate the incidence of MLBN and identify risk factors. This single-centre, retrospective study was performed between January 2018 and November 2020, in the Maxillofacial Surgery Department, Centre Hospitalier Universitaire, Caen. Patients who underwent BSSO advancement and had cone beam computed tomography (CBCT) scans obtained preoperatively, immediately postoperative (within 1 week), and late postoperative (≥1 year) were included. Measurements were made on the CBCT images. A total of 113 patients (226 operated sides) were enrolled. Mean age at the time of surgery was 17 years; 66.4% of patients were female and 33.6% were male. MLBN was observed on 35 operated sides (15.5% of sides). Advanced age (P = 0.002) and the degree of mandibular advancement (P = 0.008) were determined to be risk factors for developing MLBN. Sex, the operated side, third molar removal, and genioplasty were not associated with an increased occurrence of MLBN. Older patient age at the time of surgery and the requirement for a large advancement should be taken into consideration by the surgeon in order to reduce the risk of MLBN by using a modified BSSO procedure or bone grafting.

How to Prevent Mandibular Lower Border Notching After Bilateral Sagittal Split Osteotomies for Major Advancements: Analysis of 168 Osteotomies

PURPOSE

Mandibular ramus bilateral sagittal split osteotomy (BSSO) has been the most commonly used technique in orthognathic surgery for mandibular advancement. However, a common complication of BSSO has been the occurrence of visible and palpable osseous defects at the inferior border of the mandible. The aim of the present study was to determine whether bone grafting of the osseous defect at surgery would reduce the defect at 1 year postoperatively compared with no bone grafting.

MATERIALS AND METHODS

The present retrospective cohort study evaluated patients who had undergone mandibular ramus BSSO for 10 mm or more of advancement. The primary predictor variable was BSSO surgery with bone grafting of the defect (graft group [GG]) versus no bone graft (no graft group [NGG]). The size of the mandibular ramus inferior border defect was the outcome variable considered within the framework of a 1-year postoperative cone beam computed tomography (CBCT) analysis. Gender, age, and the amount of advancement were also considered in the multilevel regression analyses.

RESULTS

From January 2012 to November 2016, 84 patients (168 osteotomies) had undergone BSSO surgery with 10 mm or more of mandibular advancement at the Facesurgery Center (Parma, Italy). Their mean age was 27.4 years (range, 17 to 44 years). Of the 84 patients, 40 had undergone BSSO with bilateral bone grafts (GG). The monocortical block of the iliac crest bone was used as the bone homograft. The final residual defect was measured at 1 year postoperatively on CBCT scans. The GG and NGG had presented with a mean final defect of 0.7 mm (range, 0 to 4.5 mm) and 3.0 mm (range, 0 to 5.5 mm), respectively. Complete absence of the defect was achieved in 72% of the osteotomies in the GG and 9% of the osteotomies in the NGG.

CONCLUSIONS

The use of an iliac crest bone allograft block in the gap between 2 segments during mandibular advancement of 10 mm or more substantially reduced the size and incidence of inferior border defects.

Density of the mandibular ramus (cancellous:cortical bone volume ratio) as a predictor of the lingual fracture pattern in bilateral sagittal split osteotomy

The aim of this retrospective cohort study was to evaluate the relative amount of cancellous bone in the mandibular ramus as a predictor of lingual fracture patterns after bilateral sagittal split osteotomy (BSSO). The study including 78 consecutive patients (156 osteotomy sites). In preoperative cone-beam computed tomographic (CT) scans, the volumes of cancellous and cortical bone in the BSSO surgical field were estimated. Patients were divided into two groups based on the cancellous:cortical bone ratio. We studied postoperative cone-beam CT scans for lingual fracture lines and subcategorised them according to the lingual split scale (LSS). Generalised linear mixed models (GLMM) were estimated to evaluate the association between the cancellous:cortical bone ratio and the lingual fracture pattern. There was a significant association between the cancellous:cortical bone ratio of the mandibular angle and the lingual fracture pattern after BSSO. Mandibular angles with a relatively small amount of cancellous bone showed significantly more LSS3 fracture lines (OR=1.990, 95%CI 1.043 to 3.796, p=0.043). These mandibular angles also showed more unfavourable fractures (LSS4), although this was not significant (OR=2.352, 95%CI 0.748 to 7.392, p=0.143). The relative amount of cancellous bone in the mandibular angle is significantly associated with the lingual fracture line after BSSO.

The use of xenografts to prevent inferior border defects following bilateral sagittal split osteotomies: three-dimensional skeletal analysis using cone beam computed tomography

The aim of this retrospective study was to investigate grafting in the osteotomy gap during bilateral sagittal split osteotomy (BSSO), using a xenograft and fibrin glue. Hard tissue defects in the inferior mandibular border were assessed using cone beam computed tomography scans taken 1 week and 1year postoperatively. The study group of 20 patients underwent bone grafting during BSSO (mean age 26.1years; mean horizontal displacement 8.5mm) and the control group of 20 patients did not (mean age 30.2 years; mean horizontal displacement 7.6mm). The mean height of the mandibular defects was significantly lower in the study group, but there was no significant difference in volume measurements between the groups. Grafting had a negligible effect on large displacements (9.0-15.0mm), which might have been due to an inadequate amount and/or positioning of the graft, or to poor dimensional stability. This may be resolved by improved graft positioning or by using a different kind of (xeno)graft.