If the person is your boss or an elderly, You can buy the person a new set of good quality brushes to last him/her a year (4 pieces) and a good tooth paste and mouth was as a gift for any celebration, then you just tell him/her some tips to maintain mouth hygiene.

You can also get someone close to him/her to tell him on n your behalf. I hope this helps. Thank you @simmoney for stopping by.