Your teeth seem pretty hard though, to the point that a specialist has to go over them with metal tools every year to clean them.
leptons
and... plastic is not that hard, so the teeth should be able to grind down the plastic bristles as you brush your teeth. I'd find it hard to believe that no plastic is lost during brushing of teeth.
The idea of brushing my teeth with plastic has lost its appeal for me and will never be recovered.