The aim of this study was to provide recommendations for optimal distraction parameters in animal experimental research on craniofacial DO.
The principles of orthopaedic distraction osteogenesis (DO) have been successfully applied to the craniofacial skeleton, but the latency time, rate and rhythm of distraction, and length of the consolidation period that are optimal for long-bone distraction may be suboptimal for craniofacial DO. In addition, no deleterious effects were found on the digastric muscles. The results of the present study indicate that bone formation in response to automated, continuous, and curvilinear DO at a rate of 1.5 and 3.0 mm/day is nearly identical to that with discontinuous DO at 1 mm/day. The digastric muscles had no abnormal tissue or inflammation, and PAX7, MyoD, and PCNA expression had returned to the baseline levels. The PSA occupied by cartilage and hematoma in all groups was minimal (<1.1%).
The PSA occupied by bone was similar for groups A (PSA 64.36% ± 5.87%) and B (PSA 63.83% ± 3.37%) and the control group (1 mm/day PSA 64.89% ± 0.56%) but was less than that on the nonoperated side (PSA 84.67% ± 0.86%). The ipsilateral and contralateral digastric muscles were harvested and stained for proliferating cell nuclear antigen (PCNA), myogenic differentiation-1 (MyoD), and paired Box 7 protein (PAX7).Īll 10 minipigs completed the distraction and fixation period. The control groups consisted of DO wounds distracted discontinuously at 1 mm/day and the nonoperated contralateral mandible. The percentage of surface area (PSA) of the regenerate occupied by bone, fibrous tissue, cartilage, and hematoma was determined using computerized histomorphometric analysis. The distracted and contralateral mandibles were harvested at the end of fixation. Each minipig underwent 12 mm of distraction followed by 24 days of fixation. Two groups of Yucatan minipigs underwent automated, continuous, curvilinear DO of the right mandible: group A, 1.5 mm/day (n = 5) and group B, 3.0 mm/day (n = 5). To document the bone formation and soft tissue changes in response to automated, continuous, curvilinear distraction osteogenesis (DO) at rates greater than 1 mm/day in a minipig model. Micro-vessels in the distracted nerve may have recovered more rapidly than did the nerve tissue itself. This may indicate that hypoxic conditions within the distracted nerve had recovered to normal during the early stages of consolidation. VEGF expression returned to normal more quickly than did NGF expression. NGF and VEGF appeared to have been elicited from the Schwann cells and damaged nervous tissues, and they may play important roles in the initial healing of damaged nerves. NGF expression returned to normal levels at 56 days after distraction. VEGF expression had returned to normal but NGF expression was still profoundly elevated 28 days after distraction. NGF was expressed in most of the distracted nerve tissues, but VEGF was primarily detected in Schwann cells and the neurovasorum. The levels of NGF and VEGF expression were significantly elevated on the 7th and 14th day after distraction. At 56 days, the histological features of the distracted IAN were similar to those of the control nerve. Signs of acute nerve injury, including demyelination, were observed in the distracted IAN on the 7th and 14th day after distraction. The distracted IAN and contralateral control nerve were then harvested and analysed histologically and immunohistochemically. Two animals were killed at 7, 14, 28 and 56 days after completion of distraction. Unilateral mandibular distractions (0.5mm each, twice per day for 10 days) were conducted on 8 mongrel dogs. The objective of this study was to evaluate changes occurring in the inferior alveolar nerve (IAN) subsequent to mandibular distraction osteogenesis, with regard to the expression of nerve growth factor (NGF) and vascular endothelial growth factor (VEGF).
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