Heavy Metal-Driven Oral Dysbiosis: Salivary Toxicometallomics at the Host–Microbiome Interface Across Pathologies

Microbiome dysbiosis has become recognized as an important interface connecting environmental exposures to chronic inflammatory and degenerative diseases. Although prior research has largely considered heavy metals as biomarkers of exposure and toxicity, their function as ecological modulators of host-associated microbial communities remains underexplored. The oral cavity is a distinct exposome-microbiome interface where environmental, behavioral, and intraoral metal sources converge and interact with structured biofilms and mucosal immunity. This review adopts an ecological systems perspective, interpreting chronic low-dose exposure to metals such as cadmium, lead, mercury, nickel, chromium, arsenic, and aluminum as a sustained selective force on oral microbial networks. A resilience-threshold model is proposed in which cumulative metal pressure progressively diminishes microbial community stability, alters network topology, and drives transitions toward persistent dysbiosis. These modifications are further reinforced by oxidative-inflammatory feedback loops at the host-microbiome interface, facilitating a self-sustaining ecological imbalance. Sketching on insights from microbial ecology, environmental toxicology, and host response biology, this review presents a framework that links metallomic patterns to microbial restructuring, redox imbalance, immune activation, and regulatory adaptation. The analysis emphasizes ecological perturbations from stable dysbiotic states and identifies key methodological limitations that currently restrict causal inference. By conceptualizing heavy metals as active ecological drivers rather than passive exposure indicators, this work establishes a foundation for understanding microbiome-mediated disease susceptibility within an exposome-informed systems biology framework.