Immunological mechanisms of periodontal tissue destruction

Oral infection with Porphyromonas gingivalis and induced alveolar bone loss in immunocompetent and severe combined immunodeficient mice

The suitability of a mouse model for host response in the induction of alveolar bone loss by Porphyromonas gingivalis was explored. The mouths of immunocompetent and severe combined immunodeficient (SCID) mice were infected with P. gingivalis ATCC 53977. P. gingivalis was not isolated from the mouths of these mice before infection, but was present at least 42 days after infection. P. gingivalis-specific IgG was present in sera from the infected, immunocompetent mice at the end of these experiments (42 days). Specific IgG was not present in sham-infected or uninfected immunocompetent mice, nor in any immunodeficient mice. Specific IgM was not present in any sera at 42 days. Infected, immunocompetent mice of two strains showed significant bone loss in comparison to sham-infected or uninfected immunocompetent mice (p < 0.05). Infected SCID mice, which are genetically lacking both B and T lymphocytes, also showed significant bone loss compared with sham-infected or uninfected SCID mice (p < 0.05). However, the degree of bone loss was greater in immunocompetent than immunodeficient mice: the relative amount of bone in infected mice was 77% of that in sham-infected immunocompetent mice, and 86% of sham values in SCID mice (p = 0.025). Thus oral infection of mice is a feasible model for studying the effects of host response on P. gingivalis-induced alveolar bone loss. Because bone loss was induced both in immunocompetent and SCID mice but was greater in immunocompetent mice, it appears that neither B nor T cells are absolutely necessary for bone resorption in response to P. gingivalis infection but they may significantly modulate the degree of resorption.

Gingivitis induced by gingival impaction in monkeys

Impaction of the gingival sulcus with elastic bands deforms the gingival sulcus, forming a surface for growth of bacterial plaque, compresses and causes necrosis of surface epithelium and the subjacent lamina propria. The teeth become extruded and make premature contact with their apposing teeth. During mastication, forces applied to extruded teeth probably contribute to their displacement, resulting in their mobility. An inflammatory process commences within 3 days and becomes clinically evident by 7 days. The gingival becomes red-magenta in color and is slightly hemorrhagic. Pockets 4 to 6 min. in depth form within 1 week and remain as long as the impacted substance occupies the space between the tooth and the sulcus epithelium. Removal of the impacted substance results in prompt repair, with complete restoration within 3 weeks. Such repair may be by an epithelial attachment rather than by a fibrous periodontal ligament.

The immunopathogenesis of progressive chronic inflammatory periodontal disease

Natural, humoral and cellular immune mechanisms have all been implicated in the pathogenesis of chronic inflammatory periodontal disease. However, confusion still exists as to the role played by each of these immunological mechanisms. Recently, characterization of the cell types within the progressive lesion has been established, in which four recognizable zones were described. Immediately subjacent to the epithelium lining the periodontal pocket both polymorphonuclear leukocytes (PMN's) and macrophages were seen, while cells deeper in the tissues had the morphological appearance of lymphocytes. The majority of these lymphocytes had a B-cell phenotype although a few T-cells and macrophages were found. On the advancing front of the lesion the cells had the morphological appearance of plasma cells, the majority of which contained IgG. Other cells found in this region had the morphology of plasma cells yet contained no cytoplasmic immunoglobulin, but they did contain substantial amounts of lysosomal enzymes. Similar cells have previously been described in periodontal disease; their frequent association with fibroblasts may suggest that they are important in the pathogenesis. Deposits of IgG and fibrin were found in the fibrous tissue band surrounding the lesion. These results are reviewed and, although the zones described were not anatomically distinct, by describing the lesion in this way it was possible to establish a convenient model to explain the immunopathogenesis of progressive chronic inflammatory periodontal disease. In this respect, progressive chronic inflammatory periodontal disease in man should be considered as a B-cell lesion.

Bacteriology of human experimental gingivitis: effect of plaque and gingivitis score

The plaque flora isolated from discrete dentogingival sites during a human gingivitis experiment was analyzed as a function of the plaque score and of the gingivitis score. When the gingivitis score was plotted as a function of the plaque score, a nonbleeding gingivitis was associated with a proportional increase in the Actinomyces sp. at the expense of the Streptococcus sp. In particular, the percentage of Actinomyces israelii increased significantly, while the percent Streptococcus sanguis decreased significantly. A. israelii also increased significantly when a bleeding gingivitis developed. When the plaque score was plotted as a function of the gingivitis score, A. israelii increased significantly as the nonbleeding gingivitis developed, but A. viscosus and Bacteroides melaninogenicus increased significantly when the bleeding gingivitis developed. The availability of a sufficient number of plaques with a plaque score of 2.0 permitted the examination of the interrelationship of gingivitis and flora minus the effect of plaque biomass. The bacteriological profile showed that when bleeding occurred, the levels and proportions of A. viscosus and B. melaninogenicus increased significantly. These findings raise the possibility that proportional changes in the gingival plaque flora may uniquely contribute to the development of gingival inflammation in this experimental model.

Experimental gingivitis in young and elderly individuals

The development of experimental gingivitis was studied in young elderly humans during a 21-d period of oral hygiene abstention. The state of the gingiva was assessed by the Gingival Index and by measurements of the amount of gingival exudate on filter paper strips placed at the entrance of the gingival sulcus of the lower lateral incisors and cuspids. Soft deposits were assessed by the Plaque Index and by differential counts of microorganisms in gram stained smears od ento-gingival plaque. At the end of the plaque growth period, the patients were given a thorough dental prophylaxis. Gingival condition and plaque were assessed at regular intervals during a subsequent period of controlled oral hygiene. The development of gingivitis during the oral hygiene abstention period was more rapid and more severe in old than in young individuals. Plaque accumulation was greater in the older persons. A definite difference in plaque consistency was alos observed. However, microscopic counts of various types of microorganisms did not reveal any differences throughout the period of plaque accumulation. When active oral hygiene was reinstituted, the state of the gingiva rapidly returned to pre-experimental levels in both groups. The findings of this study indicate that with age ther is an altered host response to the microorganisms of the plaque.