Radiographic measurements of alveolar bone loss in the rat.

A new method to evaluate alveolar bone loss in rodents is described. The palatal and lingual halves of maxillae and mandibles were radiographed. On enlarged positive prints, 5 vertical distances were drawn at defined sites from the cemento-enamel junction to points revealing fully intact bone structure. These were either located on the alveolar crest or at the depth of intrabony defects. These distances were recorded with a trace-reading pen coupled to a computer. Results were expressed in mm for each site separately and totals (left plus right values) for either maxillae or mandibles were calculated. This technique was compared to other methods for evaluating alveolar bone loss, using the jaws of rats subjected to a gnotobiotic regime in which the degree of bone loss was low. It was demonstrated that the measurement of vertical distances based on radiography by which also intrabony defects were defined was accurate, reproducible and more sensitive than other means of evaluating bone loss.

Alveolar bone loss in rats after immunization with Actinomyces viscosus.

We investigated a possible cause-and-effect relationship between sensitization against Actinomyces viscosus Nyl and destructive periodontal disease in RIC-Sprague-Dawley rats. Germfree rats (66) were either immunized with A. viscosus Nyl (day 20) or orally infected with A. viscosus Nyl (days 38 and 39) or both. We measured alveolar bone loss in maxillary and mandibular molars, in vitro T-lymphocyte responsiveness, and serum antibody titers. In immunized and monoassociated rats bone loss in both jaws progressed rapidly between days 37 and 72, whereas the rate of further resorption decreased until day 100. In monoassociated rats, development of bone loss was much slower, and the maximum resorption measured was, at best, half of the bone loss compared with the former group. However, no amplification of bone loss by immunization was observed in a second experiment using 63 conventional rats kept in relative gnotobiosis. Antibody titers to A. viscosus Nyl in gnotobiotic monoassociated rats were higher in immunized animals, whereas no difference was found in the respective groups of the relative gnotobiotic experiment. The fact that immunization more than doubled alveolar bone loss in gnotobiotic monoassociated rats confirms the allergic nature of the disease. The lack of such an effect under conventional conditions points to suppressor mechanisms whose decrease might convert stable periodontal lesions into progressive ones.

Cell-mediated cytotoxicity against rat fibroblasts induced by Actinomyces viscosus.

Cell-mediated cytotoxicity against syngeneic fetal rat fibroblasts that require in vitro exposure of effector cells to Actinomyces viscosus Ny1 fractions was investigated by measuring the uptake of radioactivity by fibroblasts during a 2-h pulse with [14C]aminoisobutyric acid after 1 to 3 days of coculture with splenic effector cells. By using splenocytes from inbred RIC-Sprague-Dawley rats as effector cells and syngeneic embryonic rat fibroblasts as target cells, strong cell-mediated cytotoxicity dependent on the in vitro exposure to an A. viscosus Ny1 fraction was observed, but only within a small range of effector-to-target cell ratios (3:1 to 10:1). Concanavalin A and lipopolysaccharide from Escherichia coli induced a comparable cytotoxicity, indicating that the effect might be connected with the mitogenic activity of the A. viscosus NY1 fraction. Splenocytes from rats immunized with A. viscosus Ny1 and from control rats induced similar levels of cytotoxicity in 72-h cytotoxicity assays. In shorter assays (24 h), however, splenocytes from immune animals induced low cytotoxicity, which was, however, significantly higher than that induced by splenocytes from control animals. We conclude that both antigen- and mitogen-dependent cell mediated effector mechanisms are operative in this system and that the two normally overlapping effects can be experimentally separated. This new system describes a fibroblast impairment in the presence of splenocytes and bacterial components and may provide a useful model for studying pathogenic mechanisms operative in periodontal disease.