Oh, I think they'd just scrub their teeth with it and that's it ;3 The plushie-toothpaste would be a special kind of fabric that keeps their teeth aaaall nice and pretty ^-^
(That's an adorable idea you have though, with those plushie-toothpastes and plushie-toothbrushes ^-^ )
(Oh, it would ^-^ Now it just needs to cross paths with someone who can sew ;3 )