Early Life Microplastic Exposure Impairs Mouse Incisor Enamel Formation

Microplastics (MPs) are pervasive environmental contaminants with growing evidence of systemic toxicity; however, their effects on tooth development during early life remain poorly understood. In the present study, we investigated whether early-life exposure to polystyrene microplastics (PS-MPs) affects tooth eruption, root formation, and enamel development in mice. Pregnant mice were administered 1, 4, and 10 μm PS-MPs (10 μg/kg/day) from gestation through lactation, and offspring continued exposure post-weaning. Mandibles were analyzed at postnatal days 14, 25, and 42 using micro-computed tomography, histology, scanning electron microscopy, and microhardness testing. Early-life MP exposure did not affect maternal outcomes or overall offspring growth. However, it significantly delayed molar eruption and root formation and produced incisor enamel defects, including reduced enamel length and volume, decreased mineral density, and decreased mechanical hardness. These effects exhibited particle size dependency, with 1 μm MPs causing the most significant changes. Histological analyses revealed increased proliferation of transit-amplifying cells in the labial cervical loop and postponed ameloblastic differentiation, accompanied by an incisal shift in enamel matrix deposition. Collectively, these findings demonstrate that early-life MP exposure disrupts tooth development in a size-dependent manner and identify developing dental tissues as sensitive targets of environmental MP exposure.