The purpose of our rewiew the role of nitric oxide (NO) in periodontal tissues in physiological and pathophysiological conditions. NO is produced by three isoforms of NO synthase (NOS): the constitutive, endothelial isoform, eNOS; the constitutive neuronal isoform, bNOS; and the inducible isoform, iNOS. All three isoforms are present or can be expressed in periodontal tissues. ENOS is located in the vascular endothelium, bNOS in the perivascular and soliter nerve fibers. The constitutive isoforms are present under normal (physiological) conditions. NO produced physiologically by eNOS is protective in circumdental tissues, promotes perfusion and may exert anti-inflammatory effects. The expression of iNOS is induced in inflammatory conditions, such as periodontitis. NO produced by iNOS, or peroxynitrite, its reaction product are detrimental when produced in excess in inflammation. The purpose of iNOS expression in periodontitis is presumably to produce NO and destroy the invading microorganisms. However, iNOS-derived NO or peroxynitrite may destroy the host tissues as well.Selective inhibition of iNOS may be of therapeutic utility in periodontitis.

Keywords: Nitric Oxide, Nitric Oxide Synthase