I lost a tooth to a knee while I was on top holding the hips and passing. The guy shot his knee up and kneed me right in the jaw as hard as possible. Bye tooth.
I tried it and was too out of shape to keep that fucker in my mouth..
subbed 
DrB - This week i had my first BJJ practice, after a long lay off.
I went to a new Gym, and i noticed many students wearing a mouthpiece. In my former BJJ gym and throughout my extensive time in Judo, i never came across one person wearing a mouthpiece. I've also never had 1, during BJJ or judo practice..
Offcourse, i can see the benefit of it. It's a contact sport, and there's always the chance of damaging your teeth. But i would like to know: If you train BJJ (or Judo) do you wear one?
Wear a mouthpiece man. If you get a custom one you won't even know you are wearing it
Foolish not too IMO.
I wear one. Sometimes when you're rolling with a new white belt or a spazzy blue belt, or a 6'8" 325 lb monster, it's better to have your teeth protected in case a nasty knee comes through or etc in a scramble. All it takes is one time, and assuming you roll for years, you're bound to get hit in the face or bite your tongue. Plus it helps with your confidence knowing your teeth won't get fucked up.
A cup isn't necessary. You learn to roll so your balls don't get smashed and they're illegal in tournaments.
Its a simple equation really. Its based on the number of meatheads in class. If that number is >0 then it may be a good Idea 
I always wear one .. Last week a guy at my gym lost a tooth while sparring
I never have wore a mouthguard in BJJ! all my teeth are chipped to fuck! I have never lost a tooth but have had to have work. Only last week one of my training partners lost half a front tooth.
I have to cause when I roll and Evan spar I push my teeth together really hard and can't help it lol.. But also helps with accidents
I don't use a mouthpiece or a cup in judo or bjj. I have good insurance though.
I even wear mine while doing Cardio. I have a moulded one and I just feel more comfortable with it in while training.
Humboldt - Foolish not too IMO.
I'm with him. I do both. I bit through my tongue and got flying knee'd in the balls. That's learning the hard way.
Never wore one for BJJ.
Our instructor doesn't let us roll without one. I have been hit with so many knees and accidental kicks when people pass guard that it is worth it.
I wear a cup and a mouth guard at EVERY training session, BJJ, Muay Thai, Freestyle Wrestling; even wear my gumshield when out running sometimes.
My teeth are shit, basically; and I want to keep what I have left
Dude, just get one. There is no dental procedure they will help you avoid that is cheaper than they are. I think I got a Gladiator for like, $60 bucks or something last time I bought one. Your dentist can make you one also.
I wear one and like others do, I wear it even during cardio.
I chew gum while I'm rolling. No dental injuries in 3+ years of BJJ.
I also only roll with the people at my gym that can roll with some measure of control. That dude that only has one speed, that's 85% strength/15% technique, and always has his ego on the mat...he doesn't get to roll with me.
I also don't wear a cup anymore. I find it keeps me from getting lazy with my hips.
Dental work is expensive, spend the money and get a custom mouth piece