Here's a solid reference: FDA's chewing gum page explains gum base ingredients and regulation: https://www.fda.gov/food/food-ingredients-packaging-grocery-products/chewing-gum. In short, gum bases are largely synthetic polymers like polyvinyl acetate, but robust evidence that they shed microplastics in saliva is limited; consult peer-reviewed studies and SDS/technical sheets for specifics.
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