Role of nitric oxide in orthodontic tooth movement (Review)

Nitric oxide (NO) is an ubiquitous signaling molecule that mediates numerous cellular processes associated with cardiovascular, nervous and immune systems. NO also plays an essential role in bone homeostasis regulation. The present review article summarized the effects of NO on bone metabolism during orthodontic tooth movement in order to provide insight into the regulatory role of NO in orthodontic tooth movement. Orthodontic tooth movement is a process in which the periodontal tissue and alveolar bone are reconstructed due to the effect of orthodontic forces. Accumulating evidence has indicated that NO and its downstream signaling molecule, cyclic guanosine monophosphate (cGMP), mediate the mechanical signals during orthodontic‑related bone remodeling, and exert complex effects on osteogenesis and osteoclastogenesis. NO has a regulatory effect on the cellular activities and functional states of osteoclasts, osteocytes and periodontal ligament fibroblasts involved in orthodontic tooth movement. Variations of NO synthase (NOS) expression levels and NO production in periodontal tissues or gingival crevicular fluid (GCF) have been found on the tension and compression sides during tooth movement in both orthodontic animal models and patients. Furthermore, NO precursor and NOS inhibitor administration increased and reduced the tooth movement in animal models, respectively. Further research is required in order to further elucidate the underlying mechanisms and the clinical application prospect of NO in orthodontic tooth movement.