Nerve harvesting procedures

Autogenous nerve grafts currently set the standard for reconstruction of motor and sensory nerve injuries that cannot be repaired by mobilization, advancement, and approximation, and suturing without tension. Donor nerves such as the GAN and SN are easily accessible and frequently used in maxillofacial microneurosurgery. Other nerves (MACN, LCNF, LTN) may serve well in special nerve reconstruction situations. In the future, availability of biodegradable nerve conduits with neurotrophic factors may render obsolete the reconstruction of the short-span nerve gap (< 3 cm) by autogenous nerve grafts.     

牙种植术中的神经损伤

牙种植已被国内外大量的临床应用证明是缺牙理想的修复方式.与任何外科手术一样,牙种植手术不可避免地会出现一些并发症,其中常见三叉神经分支损伤.Goodacre等[1]分析了1981至2001年英文文献中关于种植并发症的报道,因种植外科手术所致的神经损伤发生率平均达到7%,仅次于出血.最常见的神经损伤有下牙槽神经、颏神经、舌神经及眶下神经损伤,这些神经受损后主要表现为不同程度的感觉功能障碍.口腔种植医师必须对此有所认识,术前采取必要的预防措施并在出现损伤时做出适当的诊断和处理.     

Nerve regeneration through collagen tubes

Severe nerve injuries may require microsurgical grafting to span a defect. Introduction of graft material into a highly vascular recipient bed is documented to aid in early regeneration of neuronal blood supply. A silicone rod (SR)-induced fibrovascular sheath was employed to evaluate the regeneration of rat tibial nerve through 2-mm-diameter collagen tubes (CT) or contralateral nerve autografts (AUTO). At first operation, 5 mm of right tibial nerve was resected from 30 retired male breeder Sprague-Dawley rats. Resected nerve was replaced with either a 5 X 2 mm SR or the nerve ends were sutured to the intermuscular fascia. Four weeks later, animals were repaired by replacing the SR with either a CT or a contralateral AUTO from the left tibial nerve. Three months later, EMG testing was performed, and histologic sections were prepared. The EMG latency and the size of the compound action potential for sheathed or non-sheathed CT or AUTO were statistically superior to controls at the 95% confidence level. All other intergroup comparisons of latency and action potential size were statistically insignificant. The proportion of nerve fibers traversing the surgical sites was not influenced by the method of repair or by the presence or absence of sheathing. Tubulized repairs most closely resembled unoperated nerves, and autografted repairs had a large diameter, but much fibrosis, whereas controls displayed immaturity and disorganization. Our observations suggest that there was no difference between repairs performed with or without a vascular pseudosheath. However, CT supported regeneration better than did AUTO repair.     

Nerve interactions in salivary glands

In the salivary reflex, not only secretory cells are activated, but also myo-epithelial cells are contracted to support these cells and promote the flow of saliva, and blood vessels dilate to meet the increased demands of the tissues. The various effector cells often receive nerves from both parts of the autonomic system, and interactions may occur when the nerves act on the same type of effector, or on different types of effectors. While in an experiment electrical stimulation of the sympathetic trunk may decrease a parasympathetic salivary flow by causing marked vasoconstriction, this does not occur in the salivary reflex, since the vasoconstrictors do not take part. On the contrary, the normal sympathetic vasoconstrictor tone of the resting gland is easily overcome by activity in parasympathetic vasodilator nerves when secretion starts. Pronounced synergism can be demonstrated between sympathetic and parasympathetic secretory nerves. In dogs, for instance, in which sympathetic secretion is beta-adrenoceptor-mediated, this is marked in the case of fluid secretion. In rats and rabbits, in which beta-receptors elicit secretion of amylase, the potentiating interaction among the nerves is striking when amylase secretion is considered. Even the random release of acetylcholine from the post-ganglionic parasympathetic axons, by itself insufficient to evoke secretion, can increase the sympathetic effects. Motor nerves interact with secretory nerves by causing myo-epithelial contraction, mechanically promoting secretion. Interactions between the nerves in their long-term regulatory function on the sensitivity of the acinar secretory and myo-epithelial cells can also be demonstrated.