I'm not a dentist, but I've trained Muay Thai... I can handle google pretty well. Take my advice with a grain of salt
http://www.rogerknapp.com/medical/tooth_knocked_out.htm http://www.health.harvard.edu/fhg/up...ate0605d.shtml
Looks like you might need a "splint" procedure if it is bad. Milk appears on all the pages, so I think milk would be ok. Looks like you want to push it in place and bite down on gauze.
I can't stress enough that I am not a dentist though... personally, I would make some calls to 24hr health places and see if they have some numbers. While you are at your dentist I'd recommend getting his number for emergencies in the future, I doubt s/he would mind. I have my dentists cell #, fortunately I've never had to use it.
Don't blame the new guy. Assuming you are an experienced thai fighter you should have reacted to the wild knee, you know how the boxing referees always say protect yourself at all times?. Unless he really reefed on your neck and you were bent over at 90 degrees, which also shouldn't have happened I can't see how he got you in the face haha. But accidents happens.
I'd also recommend getting a high quality fitted mouth guard, you might be more comfortable wearing it while training then, just be sure to clean it after every use. When I was a new fighter the steel can and the fitted mouth guard were my best investments aside from my gloves.