Micro/Nanoplastics and Periodontitis: An Environmental Microbiology Perspective on Oral Retention and Systemic Risk.

Micro- and nanoplastics (MNPs) have now been detected in human blood, placenta, and arterial tissue, yet the oral cavity has received strikingly little mechanistic attention despite serving as a primary portal of environmental exposure and a local site of polymer generation from dental and oral-care materials. This narrative review addresses that gap from an environmental microbiology perspective, synthesizing recent literature on periodontal disease, chronic low-grade inflammation, oral biofilms, dental materials, microbial-plastic interactions, and systemic chronic disease risk. Unlike prior reviews, we apply an explicit three-tier evidentiary framework (established, plausible, unproven) that distinguishes what is directly demonstrated from what is biologically plausible but unproven, and we situate the periodontal environment specifically as a particle-retention and inflammatory-amplification niche. The strongest direct oral evidence shows that human dental calculus harbors at least 26 microplastic types, dominated by polyamide (41.4%), polyethylene (32.7%), and polyurethane (7.0%). Polyethylene isolated from calculus induces cytotoxicity, apoptosis, impaired migration, NF-κB activation, and upregulation of IL-1β and IL-6 in human gingival fibroblasts. From a microbiological standpoint, oral organisms actively degrade methacrylate dental polymers, and the degradation products of these polymers reciprocally modulate oral bacterial virulence gene expression. Across experimental systems, MNPs activate oxidative stress, inflammasome signaling, macrophage polarization, and barrier dysfunction, pathways that overlap extensively with periodontal pathobiology. Adjacent environmental microbiology demonstrates that plastic-associated biofilms enhance extracellular polymeric substance production, quorum sensing, pathogen persistence, and antibiotic resistance gene transfer, supporting a plausible but not yet validated oral plastisphere within plaque and calculus. We argue that periodontitis should be reconceptualized as a chronically inflamed particle-processing interface that may increase local MNP retention, cellular reactivity, and systemic inflammatory spillover, with implications for cardiovascular, metabolic, and other chronic disease risk pathways. Current evidence does not yet prove that environmental MNP exposure causes human periodontitis, and that evidentiary boundary is maintained throughout. A priority research agenda is proposed, centered on contamination-controlled subgingival biomonitoring stratified by periodontal status, spatially resolved multi-species biofilm models, polymer source attribution, and longitudinal clinical studies linking oral plastic burden to inflammatory and systemic outcomes.