Permeability of rodent junctional epithelium to exogenous protein

It has generally been assumed that oral sulcular epithelium, being nonkeratinized, is a vulnerable region which allows bacterial products to pass from the gingival sulcus to the subjacent connective tissue. It has also been suggested that inducing keratinization of the oral sulcular epithelium might create a better barrier to such material. However, this approach ignores the effect of a permeable junctional epithelium, for if exogenous material penetrates this epithelium then the presence of keratinization may be unimportant. Rats possess an orthokeratinized oral sulcular epithelium and so represent what might be considered as an ideal sulcus lining. The protein tracers horseradish peroxidase or microperoxidase were instilled into the gingival sulcus of anesthetized rats. After 1 h, the animals were killed and fixative applied topically and by perfusion. The mandibles were detached, decalcified in EDTA to permit removal at the gingival attachment and sectioning, reacted with diaminobenzidine and H2O2 to visualize the tracer, and prepared for light and electron microscopic examination. Controls consisted of: a) animals that had not been treated with horseradish peroxidase, and b) horseradish peroxidase‐treated animals incubated without H2O2. Microscopic examination revealed penetration of the tracers through the junctional epithelium and into the underlying connective tissue, but never through the adjacent oral sulcular and gingival epithelium. These results suggest that material placed in the sulcus can enter the connective tissue via the junctional epithelium even when the adjacent oral sulcular epithelium forms a keratinized barrier.