I'm so sorry this happened to your dog!!!
While I agree with Odin24 that the kennel is not paid to ensure that your dog behaves himself 24/7, IMHO, it is paid to take basic care of the dogs including seeking medical help when there is a problem and to do something to enssure that the behavior doesn't continue once the problem is noticed. Certainly broken teeth, scabby sores on the muzzle and hot spots would be something that should be attended to by a licensed vet and the dog's behavior modified.
Many years ago the same thing happened to my shy, fearful dog, Echo. I got back from a trip and his teeth were broken, bloody spots were on his face and other areas, etc. (he was white and these big red bloody spots and dried bloody spots were easy to see a mile off). I knew he was a ditz when I left him, but had no idea he'd misbehave in such a way. But what upset me the most was the guy who ran the kennel hadn't even noticed there was a problem (and it was very obvious), and didn't say a word until I mentioned it to him. He was clueless and even after I said something he was like so what? I never went back and told all my friends to avoid the place.
Gayle ... Slider, Bruiser & Faith
At the Bridge: Andy, Abbey, Tasha, Tex, Echo, Yukon, JR, Too, Niki, Bo, Ringer, Kelly, Honey & Mac