Electron Microscopic Studies of the Normal Human Buccal Mucosa

This study was undertaken in order to describe the fundamental differences between normal skin and the oral mucosa mainly from the standpoint of keratinization.A brief survey of the literature dealing with the human oral mucosa reveals that Sognnaes and Albright (1,2), Fasske and Themann (3), and Zelickson and Hartmann (4) have done electron microscopic work on the human oral epithelium, Listgarten (5) and Kurahashi and Takuma (6) on the human gingival epithelium, Melcher on the oral connective tissue (7), and Frithiof and Wersall on some organelles (8). Until now, however, no electron microscopic work has been done on the posterior buccal mucosa of the human oral cavity, although the anterior buccal mucosa has been studied by Zelickson and Hartmann (4); and there has been no comparative study of the human mucous membrane with either adult or embryonic human skin.In this study it was found that the normal human posterior buccal mucosa is very similar to the immature embryonic epidermis in all aspects; and that despite a complete lack of keratinization, the plasma membranes of the posterior buccal epithelial cells in upper layers become considerably thicker than those of the lower layers, thus suggesting that this thickening process is a phenomenon independent of keratinization.MATERIALS AND METHODSBiopsy specimens were taken from the normal human buccal mucosa, posterior or lateral to thesecond molar tooth, of ten healthy white men and women between the ages of 17 and 50. Five specimens were obtained from the oral lesions of pemphigus vulgaris, and one from the lesion of stomatitis of the posterior buccal mucosa. All specimens were immediately sliced into small pieces, fixed in 1% osmic acid in veronal buffer (pH 7.2) containing 4.5% sucrose. After fixation for one hour, the tissues were dehydrated through a series of graded alcohols and propylene oxide, and were embedded in Araldite. Thin sections were then cut with an LKB Ultrotome at 400-600 A. The sections were stained first with 1% uranyl acetate in 50% etha-nol, and then, before completely dried, re-stained with lead citrate (9). Some specimens were stained for acid phosphatase before osmic acid fixation using the method of Barka and Anderson (10).RESULTSBasement membrane and basal layer. The basement membrane measured approximately 600 A in thickness. Occasionally, phagocytes, lymphocytes, and leukocytes were seen crossing the basement membrane (Fig. 1). In such areas the subepithelial reticular fibrils were thick, and re-duplication of the basement membrane, as reported by Caulfield and Wilgram in erythema multiforme (11), was observed (Fig. 1). The basal cells here contained fewer tonofilaments than the epidermal basal cells (Fig. 1). Intercellular spaces were rather wide, with numerous slender villi of the basal cells projecting into them (Fig. 1). Some basal melanocytes contained well-developed, rough-surfaced endoplasmic reticulum and were actively producing all gradients of maturation of melanin granules in their melanosomes (Fig. 2). The dendritic processes of these melanocytes, found between the basal cells and squamous cells, contained a greater number of more mature (larger and denser) melanin granules than did the body of the melanocytes. This phenomenon can be explained by assuming that the melanocytes inject their melanin granules into the surrounding cells as soon as the granules reach maturity. The basal cells and the squamous cells contained varying numbers of injected melanin granules (Fig. 2).As the basal cells moved up into the squamous512ULTRASTRUCTURES OF THE BUCCAL MUCOSA513*-i