Does a permanent retainer on the bottom cause a lisp at all?

I get my braces off this wednesday, and I have to have a permanent retainer on the back of my bottom teeth. I got my braces late because my teeth were really messed up, so i had to do various other ortho stuff 5 yrs prior. Anyway, I'm in college now, and have a public speaking cl, so I can't really lisp, so I can take out the removable one just for the speech, but I have to leave in the permanent one obviously. Does just a bottom permanent retainer cause a lisp AT ALL? Even if it's only a couple days, I need to know, so I can tell my instructor why I talk different. Thanks guys.