Seems like they do have teeth...I just found this....
Every time I look closely at a betta’s face, I think of bulldogs. Of course bettas are prettier, but still, their jaw is proportionally just as impressive. The lower jaw is powerful and will shred any live worms, mosquito larva, brine shrimp, etc… The mouth is perfectly designed and positioned to devour as well as to blow bubbles, which, as you all know by now, is two of Mr. Betta’s favorite pass times.

Bettas are voracious and if you ever try to stick your whole arm in a 60 gal tank filled with adult bettas, you will know just what I mean. AOUTCH!!!! Those guys keep biting the inside of my arm and it hurts! Like needles. Used to make it hard for me to care for my live plants. I have nicknamed them “my little piranhas” hehehehe. The same jaws can do wonders on another betta’s fins. One of my females once SHREDDED a gorgeous DT male to the point where he had no fins left. He looked like a female!! I was told by the Animal Planet crew that proprotionally, bettas had bigger and stronger jaws than... JAWS himself. Watch out great white sharks, here comes the bettas! It's a good thing bettas are small, cause on a larger scale they would be quite a handful! The might is lined with pointy teeth that work kinda like a paper shredder: CHOMP CHOMP CHOMP. When bettas latch on to each other's fins they do not let go. Actually the fins will tear and the aggressor usually leaves the scene with a nice chunk of fin in his mouth, which he then proceeds to promptly gobble up (remember what I said? Fighting and eating are their favorite pass times LOL).
But there is more to the mouth than meet the eyes. Beyond that intimidating row of sharp teeth, lays a warm, safe place for the fry. For the bettas will carry their young inside that same mouth formerly used to chew up their food and rivals. How such an aggressive fighter can be such a gentle parent is always a sort of amazement to me. How can a male catch his falling fry in his mouth and then gently take them back to the nest and spit them out, alive and well, without harming them? Ahhhhh... The wonders of mother nature. What's most, how come the fry don't get stuck between his teeth? I always wondered about that, until the day I caught a betta (late at night) discretely flossing ;P. Because bettas floss on a regular basis, they never get cavities. Hence you will not have to worry about ever having to take your betta to the dentist LOL. So bettas are a low maintenance pet. (I think I need a vacation)...
Betta Talk