Figure 4. Brushing induced penetration from the oral cavity of fluorescein-labeled dextran into underlying connective tissue. Paired DIC (DIC) and fluorescein dextran-derived fluorescence (FDx) images are shown. (A,B) The maxillary gingival epithelium was bathed for 1 min in fluorescein-labeled dextran but was not otherwise perturbed. No penetration of the fluorescein-labeled dextran beneath the outermost strata of the epithelium is observed. (C,D) The tongue was bathed in fluorescein-labeled dextran, but was not otherwise disturbed. As in the case of undisturbed gingival epithelium, no penetration of fluorescein-labeled dextran was observed beneath the most superficial strata of the epithelium. (E,F) The mandibular gingiva was bathed for 1 min in fluorescein-labeled dextran and then brushed for another min. Penetration of fluorescein-labeled dextran between epithelial cells and into the underlying connective tissue is not observed. (G,H) The tongue was bathed in fluorescein-labeled dextran and then brushed. Enhanced penetration of the fluorescein-labeled dextran probe was not induced by brushing of this epithelium. Magnification bar = 50 µm.