Oral mucosa is made of stra tifi ed oral epithelium(that forms the surface) and subjacent connective tissues Alt hough oral mucosa lines the oral cavity, and thus provides a barrier between external and inte1'na l(tissue) envi1'onment, it exp1'esses regional va1'ia tions in its clinical appearance based on its structu1'e(ker atini zation/ non- ke1'atini zation; nature of connective tissues ; vascul arity, etc.) . The structu1'e of or al mucosa a lso reflects its flln ctional adapta ti on. Available liter ature indicates t hat oral mucosa may be viewed as masticat ory, lining 0 1' specialized types, aJl of which remains continuously moist and unexposed to light. Oral mucosa, however, is subj ected to daily wear and tear due t o the natllre of food , environmental chernicals , t oxins and met abolites. Hence, an understanding of the biological behavior of its constituents cells and ext1'acellular matrice s , tha t• are in constant s tate of adapt ive changes, is usefll l. Oral epithelium is a multi - Iayered and multi - functional dynarnic system that separates the o1'al environment f1'om the va1'ied nature of the s llbj acent connective tlsslles The connective tissue is eithe1' loose or dense collagen ous, muscula r or osseous, and may contain glands. Thus,oral epithelia play a critical 1'ole in the mainten ance of homeost atic effi ciency of the environment of both the o1'al cavi ty and subj acent connective tisslles. The structure and fllncti ons of the oral epithelial cells are regulated by a complex interplay between genetic and environmental fa cto1's, the knowl edge of which is unfolding only recently. The fundamental prernise on whi ch 3-dimensional organization of oral epithelial integrity and st a bility are maintained is the principl e of st eady-state syst em. The basic featU1'e of the steady- st ate syst em is t he 1'egulation of cellula1' and t issue homeost atic mechanisms. Since during its ontogeny, oral epithelial cells are subj ect ed to daily wear and tear , resulting from external mechanical and chernical facto1's, a 1'eservoi1' of cells, with regene1'ative capacity(va1'iously labeled in lite1'ature as p1'ecurso1' ceJls, p1'ogeni tor cells OI‘ stem cell s) that can maintain the steady-state system of oral epi thelia, are 1'equired. Such a reservoir of cells are located in the basal layer of oral epithelia. These cells proliferates, differentiate into ker atinocyt es, and are lost through desquamation or a poptosis to maintain the steady-state syst em and thus equilibrium of tissue homeostasis

• Ravindra M Shah(Faculty of Dentistry & Medicine, University of British Columbia)