Apical periodontitis induced by selected bacterial strains in root canals of immunized and nonimmunized monkeys

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Abstract
Experimental infections in root canals with Streptococcus faecalis ssp. liquefaciens (Strep-MC4), Actinomyces bovis (Act-MC6) and Bacteroides oralis (Bact-MC3) were studied in 4 immunized and 5 nonimmunized monkeys. The immunization was performed using antigens of the homologous strains. The antibody level was checked by gel diffusion. In 56 root canals of the immunized animals and 60 root canals of the nonimmunized animals, viable cells of the 3 bacterial strains were enclosed in equal amounts in various combinations. After 6 mo., samples from the root canals were subjected to qualitative and quantitative bacteriologic analyses and the apical area was radiographically and histologically examined. The analyses revealed no significant difference between the 2 groups of monkeys, although the viable cell recovery was slightly higher in most of the root canals of nonimmunized monkeys. The cell proportion of the strains within the different bacterial combinations was equal in root canals of the 2 groups of animals. The radiographic and histologic examinations revealed no significant difference between the 2 groups regarding the number of teeth with periapical lesions. The radiographic examination, however, showed a more distinct limitation of the process in the immunized than in the nonimmunized monkeys. Histologically the lesions were more encapsulated and had a sparser cell infiltration in immunized than in nonimmunized monkeys. In the latter, inflammatory cells had often infiltrated the bone. Mixed infections gave a more severe periapical reaction than single strain infections in both groups.