Open sore under chin?!

Hi everybody, I'm new here... I joined because I have a serious question about my three year old cat Domino. Yesterday my dad noticed blood on Domino's usually white chest. Anyways, after he inspected it he saw a small sore that he described as a "hole". The problem is... Domino hates my dad, and is really only friendly with me. And "friendly" is relative. Domino doesn't like to be held, and really doesn't stay on my lap for more than a few minutes at a time, so it was hard to get a good look at the sore. 

Eventually I managed to grab him by the scruff and stradle him (to impair any claw action) and what I saw was no small sore. 

It does look like a hole, like my dad said... but it is leaking and bloody and red and purple...

So I continued to hold him and cleaned off the blood with a wet paper towel. then I got some peroxide in a syringe and flushed the hole with is to kill any infection. Without all the blood and oozy stuff it was a lot easier to see, and I began to suspect the hole went all the way into his jaw.

Domino has had gingivitus for about a year. We have tried some cheap water supplements and mouth spray, but we can't afford the all-tooth extraction the vet recommended. So my thought was that one of his nasty infected roots had rotted through his jaw and out his chin. But theres no sore inside his mouth, and I really can't hold him down long enough for more than ten minutes of abuse

So anyways, I then read that it's not good to use peroxide because it damages tissue (whoops) so I tried to bandage him up and leave him alone so he wouldn't hate me forever. 

Today, the hole looks less like a hole and more like a sore, and I would totally clean out the blood so it were easier to see, but I would like it to scab a bit and see where it goes. 

So here are some pictures, and I would really like some opinions on what it could be, and whether this is really urgent (I believe my vet tends to overcharge, and we just had a lot of stuff done to our other cat, so we would like to save money if we can)

I wish I had an answer for you.  Once, my dog showed up with a similar hole under his chin and it was a puncture wound from a dog bite.  I know most animals go for the neck region when they bite, even in play.  Do you have other cats?  Is it possible that he was in a fight or was playing rough with another cat/animal?  It could also be an abcess if it's draining a lot.  I don't know much about gingivitus in cats, but it seems to me that the wound would have started on the inside. 

I think a trip to the vet might be in order.  (((HUGS)))

If it is an abcess, it may need antibiotics? Was there any pus or other signs of infection?

You could try emailing the pictures to your vet and see if they will prescribe antibiotics over the phone to a local pharmacy.

Domino is an indoor only cat, and his companion had to be put down about two weeks ago, so I don't think it was another cat or dog. I do have a couple guinea pigs, but I don't think they could have bit him, especially not on the chin. He is pretty scared of them! It takes a while to dry up after I clean it, but it still seems like some sort of fluid is coming from the sore. Last night when he layed on me while I was under a blanket, he left a diluted blood spot where the wound rested. Even after cleaning, I notice new discoloring on his white chest fur. The only signs of infection are the purplish color of the skin in the wound itself, and his regular mouth infection-type stuff. 

If you don't think an injury is likely, then a vet visit is in order, especially since you know he has problems in his mouth. Many vibes that it's not serious and quickly healed.