Periodontal Microbiology Study Notes

Periodontal Microbiology Study Notes

• Biofilm Maturation: Dental pellicle forms from saliva, GCF, and bacteria, providing a substrate for bacterial adhesion within minutes on clean enamel. Primary colonizers (gram-positive facultative aerobes like Streptococcus and Actinomyces) attach first, followed by secondary colonizers (gram-negative anaerobes like Prevotella, Capnocytophaga, and Fusobacterium). These later colonizers, particularly the "bridging species" like Fusobacterium nucleatum, connect early and late colonizers and drive biofilm maturation. Colored complexes are groups of bacteria with linked pathogenicity, like the red complex (most pathogenic).

Colored Complexes

• Red Complex: Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola are the most pathogenic.
• Orange Complex: Fusobacterium nucleatum (bridging species) and Prevotella intermedia along with Parvimonas micra and Campylobacter rectus has moderate, but precedes the red complex.
• Yellow Complex: Streptococcus spp. (S. mitis, S. sanguinis, S. oralis, S. gordonii) are early colonizers.
• Green Complex: Aggregatibacter actinomycetemcomitans is associated with aggressive, but variable pathogenicity in this complex.

Plaque Hypotheses

• Non-Specific Plaque Hypothesis: Plaque accumulation surpasses host defenses, leading to disease. All plaque contributes to periodontitis. This hypothesis is incomplete as some individuals have high plaque but no disease, showing other factors are involved.
• Specific Plaque Hypothesis: Certain bacteria are solely implicated in periodontal disease (periodontopathogens). Critically, examples found in healthy people illustrate this hypothesis's incompleteness.
• Ecological Plaque Hypothesis: Environmental shifts (inflammation, low oxygen) cause a dysbiotic shift in microbial composition towards a more pathogenic community. This hypothesis focuses on restoring homeostasis within the microbiome instead of eliminating all bacteria.

Microbial Associations with Health/Disease

• Health Associated Microbes: Gram-positive facultative bacteria like Streptococcus and Actinomyces species.
• Gingivitis Microbes: Gram-positive facultative species (same as health) and increasing Gram-negative anaerobes like Fusobacterium, Capnocytophaga and Prevotella intermedia.
• Chronic Periodontitis Microbial Composition: The Red and Orange Complex species (P. gingivalis, Aggregatibacter actinomycetemcomitans, T. denticola, F. nucleatum ).
• Aggressive Periodontitis Microbial Composition: Aggregatibacter actinomycetemcomitans is a key pathogen here, accompanied by Prevotella intermedia and Campylobacter rectus.

Virulence Factors

• Periodontal Pathogens' Virulence: Adhesion (P. gingivalis to fibrinogen/fibronectin), endotoxins (LPS stimulating inflammation & bone resorption), collagenase and other matrix metalloproteinases (MMPs) breaking down connective tissue, and tissue invasion.

Biofilm Role in Periodontal Diseases

• Gingivitis: Biofilm formation is crucial for gingivitis; initial plaque accumulation induces inflammation without attachment loss unless inflammation progresses.
• Periodontitis: Biofilm is necessary but not sufficient. Periodontitis is influenced by host responses with a shift to more virulence-prone Gram-negative anaerobic bacteria and worsened factors. Critical factors involve host tissue invasion by specific species.

Periodontal Therapy Goals

• Therapy Goals: Reduce biofilm mass, disrupt dysbiotic microbial community organization to associate with healthy communities. Reduce pockets and create shallow crevices to inhibit pathogenic species.