In this well organised study the authors demonstrate the benefit of use of substance P to improve the quality of bone during mandibular distraction. Substance P is a neuropeptide that is distributed in those sensory nerve fibres that innervate the medullary tissues of bone. It is a potent accelerator of proliferation and differentiation of osteoblasts in vitro. However, its capacity for promoting repair of mandibular defects is not known. The authors investigated the osteogenic effects of local injections of substance P during mandibular distraction osteogenesis in rats. Twenty rats were randomly assigned to two groups (n=10 in each): substance P 10(-7)mmol/l in normal saline 0.2ml was injected into the experimental group, and saline alone into the controls. The mandibular distraction rate was 0.2mm every 12 hours for 10 days. Daily injections of substance P or saline were given during the distraction period. Regeneration of bone was assessed quantitatively on days 15 and 29 using microcomputed tomography (microCT), and histological analysis. The rate of bony union in the group treated with substance P was significantly higher than that in the saline alone group on day 29 (p=0.001). The microCT images and quantitation showed more callus and more mature cortical bone when substance P was given than with control. Histological examination showed that cartilaginous tissues had formed in the middle of the distraction gaps in both groups. Bony bridges were seen only in the substance P group at the final time point. The authors conclude that injection of substance P into the gap of a rat mandible during mandibular distraction improved formation of good-quality bone and accelerated bony union.

Local injection of substance P increases bony formation during mandibular distraction osteogenesis in rats.
Zhang YB, Wang L, Jia S, et al.
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Sampath Chandra Prasad

Gruppo Otologico, Placenza, Italy.

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