Activation of Shh signaling is known to be observed following injury of the peripheral nerves such as the sciatic nerve. However, the precise role of Shh signaling during peripheral nerve regeneration is not fully understood. The inferior alveolar nerve (IAN) is most commonly injured during oral surgery. Unlike the sciatic nerve, the IAN is isolated from other craniofacial tissues, as it resides in a long bony canal within the mandible. The IAN is thus an excellent experimental model for investigating peripheral nerve regeneration. In this study, the role of Shh signaling in peripheral nerve regeneration was investigated using the mouse IAN transection model. During regeneration, Shh signaling was activated within the entire distal region of the IAN and proximal stumps. Inhibition of Shh signaling by cyclopamine application at the transection site led to abnormal axon growth in random directions, a reduced number of macrophages, and an increase in myelin debris within the distal region. Shh signaling is thus involved in peripheral nerve regeneration via the regulation of myelin degradation.
Brain-derived neurotrophic factor (BDNF), which is released due to nerve injury, is known to promote the natural healing of injured nerves. It is often observed that damage of mandibular canal induces local sclerotic changes in alveolar bone. We reported that peripheral nerve injury promotes the local production of BDNF; therefore, it was possible to hypothesize that peripheral nerve injury affects sclerotic changes in the alveolar bone. This study aimed to evaluate the effect of BDNF on osteogenesis using in vitro osteoblast-lineage cell culture and an in vivo rat osteotomy model. MC3T3-E1 cells were cultured with BDNF and were examined for cell proliferative activity, chemotaxis and mRNA expression levels of osteoblast differentiation markers. For in vivo study, inferior alveolar nerve (IAN) injury experiments and mandibular cortical osteotomy were performed using a rat model. In the osteotomy model, exogenous BDNF was applied to bone surfaces after corticotomy of the mandible, and we morphologically analyzed the new bone formation. As a result, mRNA expression of osteoblast differentiation marker, osteocalcin, was significantly increased by BDNF, although cell proliferation and migration were not affected. In the in vivo study, osteopontin-positive new bone formation was significantly accelerated in the BDNF-grafted groups, and active bone remodeling, involving trkB-positive osteoblasts and osteocytes, continued after 28 days. In conclusion, BDNF stimulated the differentiation of MC3T3-E1 cells and it promoted new bone formation and maturation. These results suggested that local BDNF produced by peripheral nerve injury contributes to accelerating sclerotic changes in the alveolar bone.
The aim of this study was to investigate the relation between frontal craniofacial morphology and the distribution of occlusal force in orthodontic patients with and without TMD. Experimental data were obtained from 45 female orthodontic patients (TMD-free group: 22 subjects; TMD group: 23 subjects) using the pressure-sensitive sheet. The following results were obtained: (1) There were significant differences in the gonial angle width and the mandibular deviation of the postero-anterior cephalogram between the two groups. (2) There were significant differences in occlusal force, occlusal contact area and average occlusal pressure between the two groups. (3) On the relation between the frontal craniofacial morphology and the occlusal data, the asymmetry indices of occlusal force and occlusal contact area showed significant positive correlations to the mandibular deviation and the ratios of maxillary and gonial angle widths in the TMD group. The TMD-free group showed the smaller mandibular deviation and the smaller asymmetry indices of occlusal force and occlusal contact area than those in the TMD group. It could be concluded that orthodontic patients with TMD may have not only the morphological disharmony but also the imbalance of occlusal force.
It was suggested that once-a-week functional training of dysphagia with professional oral care might be effective in preventing pneumonia for elderly people who were being tube fed.
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