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Effects of microplastic release from 3D-printed orthodontic aligners: a histological and immunological bioassay
Marina Borgese1, Piero Antonio Zecca1, Annalisa Grimaldi2
1Department of Medicine and Technological Innovation, University of Insubria, Via Guicciardini 9, Varese 21100, Italy.
Aim:
This study investigated the acute biological effects of micro- and nanoplastics (MPs/NPs) released from 3D-printed orthodontic aligners, focusing on their potential to elicit inflammatory and oxidative responses. Given the dynamic intraoral environment, the use of a biologically relevant invertebrate model (Hirudo verbana) enabled histological and molecular assessment of short-term exposure to plastic-derived particles.
Materials And Methods:
MPs/NPs were generated from 3D-printed aligner samples via mechanical stress and ultrasonication. Medicinal leeches were exposed to the resulting plastic dispersion for 24, 72 h, and 1 week (triplicate experiments). Morphological alterations were assessed by light and electron microscopy. CD31 and HmAIF-1 immunostaining and acid phosphatase assays evaluated immunological responses. Oxidative stress was quantified by quantitative PCR (qPCR) analysis of SOD and GST gene expression. One-way ANOVA with Dunnett's post hoc test comparing MP/NP-treated vs controls (α = 0.05).
Results:
Exposure to MPs/NPs triggered rapid angiogenesis, confirmed by increased CD31 expression and vascular remodelling over time (24 h, P < .01; 72 h, P < .001; 1 week, P < .01). Macrophage-like cell activation was significantly evidenced by elevated HmAIF-1 levels (24 h, P < .001; 72 h, P < .01; 1-week, P < .001) and acid phosphatase activity (24 h, P < .001; 72 h, P < .01; 1-week, P < .001). Oxidative-stress markers (SOD and GST) were significantly upregulated at 24 h (P < .001) and, for glutathione transferase only, slightly increased at 72 h (P < .05), indicating an acute cellular stress response that decreased at later time points.
Conclusions:
Even brief exposure to MPs/NPs released from 3D-printed aligners can disrupt tissue homeostasis, activating inflammatory and oxidative pathways. These findings raise concerns about the biocompatibility of photopolymer resins and underscore the need for more dynamic, biologically relevant testing models to evaluate the safety of orthodontic materials under clinically realistic conditions.
