Ultrastructural findings in the oral mucosa of betel chewers.
Eighteen biopsies of the oral mucosa of northern Thai hilltribe betel chewers were studied histologically and by transmission and scanning electron microscopy (TEM, SEM). Clinically, varying stages of epithelial atrophy and one case of submucous fibrosis were observed. Histologically, epithelial atrophy with marked reduction of the rete pegs, hyperortho- and/or parakeratosis, and subepithelial edema and inflammatory changes were the prominent findings. On the ultrastructural level, cytoplasmic projections of the basal cells into the subepithelial stroma were seen. The basal membrane frequently revealed gaps; the interepithelial space was widened and unusual microvilli were observed on cell surfaces (SEM). Intercellularly, cristalloid material of unknown origin was also seen. The subepithelial connective tissue was characterized by dense bundles of collagen fibres adjacent to which masses of amorphous material were located. While some of the ultrastructural findings in the epithelium of betel chewers are indicative of early dysplastic changes, the nature of the juxta-epithelial stromal alterations is still unknown. Current hypotheses regarding the etiology of oral submucous fibrosis are briefly discussed.