**1. Introduction**

Lichen planus is a chronic systemic disease of established immune-mediated pathogenesis. [1] It most commonly, protractedly and persistently, involves the mucosa of the oral cavity, but it can involve other sites, namely the skin, the scalp (with inflammation around and affecting the hair follicles) resulting in alopecia), the nails as well as the genital area - the vulval and vaginal mucosa, and the glans penis. Other sites of involvement that are far less frequently described include the oesophagus and conjunctiva. There are seven recognized oral presentations of lichen planus: (1) reticular, (2) papular, and (3) plaque-form and the (4) atrophic, (5) ulcerative (erosive) and rare (6) vesiculo-bullous form [2] and (7) desquama‐ tive gingivitis, this latter term is a clinical descriptor, used to describe inflammation, with a mix of erythema, erosion and/or ulceration of the gingival tissues and the immediately adjacent alveolar mucosa, not incited by the presence of dental bacterial plaque. These latter four forms of OLP can be associated with significant discomfort requiring either topical and/or systemic immunosuppressive therapy.

The cause(s) of the various oral lichenoid lesions, ranging from idiopathic oral lichen planus (OLP) to the "contact" lesion, is not understood, but all the lesions are characterized histologically by a typical "lichenoid tissue reaction" featuring (1) a bandlike lymphohistio‐ cytic infiltrate that fills the lamina propria; and (2) liquefactive degeneration of the basal keratinocytes. [3] These reactions may be the result of several diverse possible triggers, but all culminate in a common pathologic process, that of T-lymphocyte directed, immune mediated, damage to the oral epithelial basal cells.[1, 2]

© 2013 Schifter et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
