
I guess its halloween...
《Who remembers Mrs Marsh and Colgate Flurigard - it's WHY I won't buy their products and the "see, it does get in!"》
That is a long time ago. Apart from wondering at the time why Rod Marsh's mum was hawking this stuff :) I imagined that it would had to have been a pretty terminal case of osteoporosis for ink to penetrate teeth.
Fastforward a few decades and it does appear toothpastes containing much higher concentrations of fluoride than Mrs Marsh's offering are actually beneficial. See https://ods.od.nih.gov/factsheets/Fluoride-HealthProfessional
So she was possibly not as daft as she appeared.