Never really thought of this before, but now that you mention it.. good to think about! This nytimes article was the first source to show up on google.

This quote from an interviewee (an oral surgeon) seems to be the gist of the article (basically "it's unclear"):

"Still, researchers can’t say if dental products are a major source of microplastics, compared to other sources, Dr. Di Spirito said. In theory, microplastics could enter your body through tiny breaks in the gums, by passing through tissues in your mouth or by simply being swallowed, she added. But it’s unclear how much this actually happens, or whether most of them are spat out."

Would be cool to dig into the actual research and see if there are differing views or promising ideas.

Does flossing give me microplastics?