D5 Biological Diagnosis

Topic

Biological diagnosis evaluates two aspects of the patient: the state of the oral microbial ecosystem and the host's immune response to that ecosystem. To assess these aspects, biological diagnosis employs various laboratory methods—some targeting the oral microbial ecosystem and others the host's immune response.

The most established method for evaluating the oral microbial ecosystem is microbiological culture; this allows for the counting of *Streptococcus mutans* and *Lactobacillus* bacteria—a count used to estimate dental caries risk—as well as the counting of periodontal pathogens—a count used to estimate the risk of periodontal disease.

In addition to microbiological culture, complementary methods exist to quantify these same bacteria: a real-time genetic amplification technique detects and quantifies specific bacterial species within the oral microbial ecosystem with greater precision, while certain commercial tests allow for a simpler, semi-quantitative estimate of salivary *Streptococcus mutans* and *Lactobacillus* levels, without requiring a full microbiological culture.

The total bacterial load of the biofilm does not increase indefinitely; while it grows rapidly at first, growth slows progressively as the biofilm approaches its maximum bacterial capacity, eventually stabilizing near that limit rather than continuing to increase without bound.

Beyond counting specific bacterial species, the entire oral microbial ecosystem can be characterized through microbiome sequencing analysis; this identifies and compares the various bacterial species present based on a ribosomal gene common to all bacteria, making it possible to determine the dysbiosis profile—that is, the extent to which the oral microbial ecosystem's composition has deviated from a healthy bacterial state. To evaluate the host immune response, gingival crevicular fluid is analyzed for inflammatory markers such as interleukin-1 beta, tumor necrosis factor-alpha, prostaglandin E2, and matrix metalloproteinases; this analysis is complemented by measuring leukocyte activity and detecting specific antibodies against pathogens within the oral microbial ecosystem.

Within this same gingival crevicular fluid, the ratio between the osteoclast-activating signal and the osteoprotegerin that inhibits it allows for the prediction of periodontal destructive activity: the more the osteoclast-activating signal predominates over osteoprotegerin in the fluid, the greater the periodontal destructive activity to be expected in the patient.

Collectively, these methods yield a specific set of patient-derived variables: the number of colony-forming units per milliliter of *Streptococcus mutans* and *Lactobacillus*, the concentrations of interleukin-1 beta and matrix metalloproteinases, and the ratio between the osteoclast-activating signal and osteoprotegerin. Based on these measured variables, the biological diagnosis determines derived values ​​such as the patient's biological risk level, the dysbiosis index of their oral microbial ecosystem, and the severity of the inflammation associated with their host immune response.

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