I have four implants and crowns across the top front (7 - 10).
In the beginning, I lisped badly. My tongue would get caught up on the back of the crowns as they are much thicker than real teeth would be.
Reciting from 70 to 60 backwards over and over helped. Also, practice watching how you speak in front of a mirror and see if you can correct the words you lisp that way.
It took me a good three months before I saw any improvement and now even after two years, I still lisp slightly at night when I get tired.
It's not as noticeable to others as it is to you yourself, though.
Not one person I know has been able to hear what I think is a lisp at all.
Good luck. It does take awhile but it usually is manageable.
Best to you,
Gellia
Seeing a prosthodontist is advised.