E7 Biological Balance

Topic

The biological equilibrium of the oral system describes a dynamic balance on two fronts: between biofilm microorganisms and the host immune response, and between destructive processes—such as demineralization and periodontal inflammation—and reparative processes, such as remineralization and bone remodeling.

The healthy oral microbiota, comprising nearly seven hundred distinct species, exists in a state of eubiosis in which commensal species outnumber pathogenic ones. When oral environmental conditions change—for instance, due to a high-sugar, cariogenic diet or poor oral hygiene—the oral microbiota can shift to a state of dysbiosis; that is, a microbiological imbalance where pathogenic species are no longer kept in check by commensal species.

The periodontal inflammatory response to this microbiota is governed by a bacterial load threshold: as long as the bacterial load remains below this threshold, the host immune system successfully controls the infection without causing damage; however, once the bacterial load exceeds this threshold, tissue destruction occurs in the tooth-supporting tissues.

Alveolar bone remodeling—one of the reparative processes within this biological equilibrium—is regulated by the balance between the signal that activates osteoclasts and the osteoprotegerin that inhibits it. This is the same balance that determines the destructive periodontal activity associated with periodontal disease: when the activating signal prevails over osteoprotegerin, alveolar bone is resorbed, whereas when osteoprotegerin prevails over the activating signal, alveolar bone is formed.

Furthermore, this periodontal inflammatory response generates mediators such as interleukin-1 beta, tumor necrosis factor-alpha, and prostaglandin E2—the same inflammatory mediators quantified in gingival crevicular fluid. These mediators directly stimulate osteoclasts, shifting the balance of alveolar bone remodeling toward resorption. The acidic pH locally produced by biofilm—the same mechanism that dissolves tooth enamel during dental caries—also directly triggers alveolar bone dissolution, compounding the resorption already driven by osteoclast-activating signals and inflammatory mediators. Thus, the biological balance of the oral system described earlier shifts toward destruction when dysbiosis, a bacterial load exceeding the threshold, the predominance of osteoclast-activating signals, and biofilm acidity combine; conversely, it shifts toward repair when eubiosis, immune control of the infection, and bone formation predominate.

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