Abstract
The purpose of this study was to assess the extent of bacterial invasion into periodontal tissues during experimental periodontitis in rats. Forty-six conventional (CV) rats and 36 germfree (GF) rats were used for this experiment. Mechanical stimulation was achieved by applying a small elastic ring around the cervix of the mandibular first molar (M 1). The ring produced continuous pressure against the periodontium which eventually produced a periodontal pocket. Bacteria were introduced around the cervix of M 1 by applying 5×108 colony forming units of Porphyromonas gingivalis (P. gingivalis) in 0.05ml of saline solution, 7 days after the application of the elastic rings. Histopathological evaluation of periodontal status was made 1 hour after the application of P. gingivalis using light microscopy and transmission electron microscopy.
Results:
1. The elastic rings, applied around the cervix of the M 1, produced periodontal pockets and caused alveolar bone resorption in CV and GF rats. The degrees of inflammatory cell infiltration and alveolar bone resorption were decreased in GF rats as compared to CV rats.
2. Numerous polymorphonuclear leukocytes (PMNs) were observed on the surfaces of ulcerated areas in mechanically stimulated CV rats. Bacteria were observed in the PMN zone on the surface of ulcer. Most bacteria had been phagocytized by the PMNs. Bacteria were not observed in deeper connective tissue zone.
3. In GF rats and non-mechanically stimulated CV rats, bacteria were not observed in periodontal tissues.
Discussion and conclusion:
In these experimental models, it is rather difficult to distinguish actual bacterial invasion from passive bacterial presence in the epithelial cell layer gap. It is concluded that even though there is ulcerative lesion on the periodontal pocket wall, bacterial invasion into deeper connective tissues is effectively prevented by PMNs.
