Immunohistochemical analysis on cortex-to-cortex heal following mandibular vertical ramus osteotomy in dynamic condition

Abstract

Vertical ramus osteotomy (VRO) is a surgical method of performing an osteotomy from the sigmoid notch to the postero-inferior border of the ramus from the lateral aspect of the ascending ramus for the mandibular setback, followed by healing under dynamic condition which allows movement of bony segment. This study aimed to evaluate specific cytokines among the TGF-β superfamily at each period following VRO, and to compare those results with fibular fracture heal. The 4 beagle dogs were used for this experiments, and euthanized at 1, 2, 4, and 8 weeks postoperatively. 6 specific antibodies were used in this immunohistochemical analysis: bone morphometric protein -2/4, -7, (BMP -2/4, -7) matrix metalloproteinase-3 (MMP-3), transforming growth factor-beta 2, 3 (TGF-ß2, -ß3), and vascular endothelial growth factor (VEGF)

The results are followed:

1. In VRO heal, inflammatory cell infiltration and resorption of cortical bone at 1 week, cartilage formation by chondrocyte at 2 weeks, and cartilage resorption, primary bone formation, and vascularization at 4 and 8 weeks were observed in HE staining. In Fibular fracture heal, no remarkable differences were seen in HE staining compared to VRO heal at each period.

2. In general upregulation of BMP-2/4 was observed in whole heal periods in VRO and fibular fracture, while the strongest expression of BMP-2/4 was observed at 2 weeks postoperative following VRO in contrast to a relatively constant expression of BMP-2/4 following fibular fracture.

3. The strongest expression of BMP-7 was observed at 1 week following VRO, in contrast to constant up-regulation following fibular fracture. The decreasing pattern in VRO may be caused by dynamic movement of mandible.

4. The strongest expression of TGF-ß2 in VRO was observed at 8 weeks, the expression showing increasing pattern, meaning remodeling activity accelerated over time.

5. Strong expression of TGF-β3 was observed at 1 and 4 weeks in VRO, and at 1 and 8 weeks in fibular fracture. Up-regulation at 1 week is explained by degranulation of platelets, and up-regulation at 4 weeks in VRO and at 8 weeks in fibular fracture means indicates cartilage formation and periosteal response are activated after 4 weeks.

6. The strong expression of VEGF was observed at 1 week in VRO and 4 and 8 weeks in fibular fracture. This result means that the mandibular ramus has sufficient vascularity before injury, and that the needs for angiogenesis and vasculogenesis increased later in the case of fibular fracture.

Based on the above findings, the expressions of specific cytokines differed following VRO and fibular fracture although the healing process following VRO was similar at each period. Dynamic jaw movement is thought to be a contributing factor for differential expression of BMP-7 and TGF-β2, and anatomical factors including preexisting vascularity account for differences in expression of VEGF.