Histopathological Study on Experimental Gingivitis in Rats: The Reaction of Gingival Epithelium in Initial Gingivitis

The present study was aimed at developing an experimental model for histopathological understanding of the process of development of gingivitis from the normal gingiva and at determining the relation between response of the gingival epithelium to inflammation and deepening of the gingival sulcus (pocket formation). In the experiments, the right and left large salivary glands were extirpated from male Wistar rats to disturb the self-cleansing action. The effects of ingestion of solid or powdered food on the periodontal tissue were determined for the palatal gingiva at the upper first molars at 1, 2 and 4 weeks and 3, 6 and 9 months of being raised on these foods, by macroscopic observation, histopathological observation (light microscopy), histomorphometry, and autoradiography (tracer, 3H-thymidine). The results were as follows: 1. Macroscopic observation at 3 months or later revealed substances attached to the dental surface in some rats in both the control and experimental groups, regardless of the type of food. 2. Histopathological examination disclosed timerelated inflammatory findings only in rats given solid food in the experimental group. Exudative inflammation with infiltration mainly of polymorphonuclear leukocytes began at 2 weeks in the lamina propria of the gingiva just under the area of junctional epithelium Lymphocyte infiltration was found at 3 months, with the focus of inflammatory cell infiltration expanding toward the root apex. In the process of expansion, deepening proliferation of the epithelium over the CEJ (cementenemel junction) came to be observed, and a crevice corresponding to a gingival pocket was formed in the area of junctional epithelium and extended with time. However, there were no findings of gingivitis such as marked absorption of the alveolar bone and destruction of periodontium throughout the 9 months. 3. Histomorphometry showed a shift of the pocket bottom toward the root apex by 9 months in rats given solid food in the experimental group. Along with such changes, Oral sulcurar epithelium moved toward the root apex. In addition, while the degree of inflammatory cell infiltration just under the area of junctional epithelium increased, the number of cells composing the pocket bottom decreased. 4. Determination of the labeling index for the basal cell layer of gingival epithelium revealed that the mitotic activity of oral sulcular epithelium and in the area of junctional epithelium tended to increase with time in rats give