Microbiology and Pathology: Oral Flora, Infection, and Disease Mechanisms
Oral microbiology
Dental plaque is a structured biofilm, not a random accumulation of bacteria. Early colonizers attach to the pellicle; later colonizers coaggregate. Caries is associated with acidogenic, aciduric organisms such as Streptococcus mutans and Lactobacillus species. Periodontal disease is associated with the anaerobic red complex - Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola - with Aggregatibacter actinomycetemcomitans implicated in aggressive forms.
Sterilization and control
Sterilization kills all microorganisms including spores; disinfection does not. Autoclave conditions are approximately 121°C at 15 psi for 15 minutes, monitored with biological indicators such as Bacillus stearothermophilus spores (dry heat uses Bacillus atrophaeus). Glutaraldehyde is a high-level chemical disinfectant.
General pathology
Distinguish acute from chronic inflammation: neutrophils versus lymphocytes, macrophages, and plasma cells, with granuloma formation in chronic states. Differentiate necrosis from apoptosis, and benign from malignant neoplasia using differentiation, mitotic activity, invasion, and metastasis. Carcinomas arise from epithelium and sarcomas from mesenchyme. Review the four hypersensitivity types: I (IgE/mast cell), II (antibody against fixed antigen), III (immune complex), IV (T cell mediated, delayed).
Traps
Questions swap which organism belongs to which disease complex, or describe a delayed reaction while offering IgE as the answer. Sterilization versus disinfection is a frequent distractor, as is the notion that a disinfectant reliably destroys spores.
Rule of thumb
Match the hypersensitivity to its mediator: IgE for type I, IgG/complement for II and III, T cells for IV.