Picked a guy up off the track and when I had his teeth done we found that he has a scar all around his tongue (we’re guessing it is from a bit accident, a wire bit or an extremely tight tongue tie). Luckily he’s easy U/S for the most part. A push type ride. Learning slowly about proper frame work. Hes in a regular jointed rubber snaffle now and doesn’t seem to mind it but would like to find a better option if anyone has an idea. Thanks!
I have had great success with the Flexi Mouth Rubber Peanut Loose Ring, it is smaller in diameter than the Happy Mouths and a bit less expensive. . . Horses seem to love them, and my OTTB who is quite sensitive (no tongue scar though) likes this better than the Nathe or Duo, which is fine with me! It’s a lot less expensive!
I don’t think tongues can grow scar tissue, so do you just mean it has a notch or dent?
I have had horses with partially cut tongues (apparently common around here…people who put round bales out but don’t cut the string, so the horse slices its tongue on the string). As the horse still has normal sensation in the area, I haven’t found a special bit to be needed, but then I almost always use a double jointed bit with a “bean” in the middle.
My OTTB didn’t have a mouth related injury, but she sure was hard to find the right bit for. I finally just started trying as many different bits that I could until she picked the one she liked. I borrowed bits from friends at the barn, because I’d own 20 different bits by now if I’d had to buy them to try. 
All my horses love a lozenge or bean in the middle of their bits, but she does best in a hollow mouth, thick eggbutt snaffle.
My TB goes best in the Herm Sprenger Duo bit with the D rings.
I have my guy with a sensitive mouth in a French link.
