Dental Health

I’ve recently started working with a 3yr old mustang. His teeth are black and he has these white(ish) round spots above two of the teeth. Today after a light session (in only a halter) there was blood in his mouth. He is a heavy drooler as well. We washed his mouth out with a hose (which became a fun game for him so didn’t seem to cause any pain) and checked his mouth later to find no blood. I have never seen anything quite like this and was hoping someone else had and could tell me what is going on. I would like to have him start carrying a bit soon, but not until this is figured out. I don’t want to cause him any pain or build bad associations during his training. Thanks for any help. P.S. while I would like a vet consult, this is not my horse. I am just training him (although I won’t if there is a problem with his health). Thanks again in advance.

Black teeth sound like dead teeth to me, which means the white spots could be signs of infection. Hard to say without a picture, but I’d be pushing for a vet who does dentistry to take a look.
At 3 he should definitely be having his teeth done anyway.

How “3” is he? Barely 3? 3.5? Could he be younger and is shedding baby caps, which can make the teeth look all sorts of wrong, including food accumulating between the old and new, and some bleeding?

Can you get a picture?