Cochise got a abcessed tooth while staying at the trainers, it blew a small hole out his lower jaw and gunk was coming out of it...at first we thought he had cut himself but after the vet looked at it he said it was a abcess. He was put on antibiotics for a time..and was advised by the vet if that worked and no further issues other than keeping an eye on it I should be fine. Knock on wood...its been a year since it healed, had his teeth floated last month..and all is good so far. The vet said nothing further needed unless it came back. And it looked to be simular to your picture..the vet explained the infection had to go somewhere and it was a probably a good thing it forced itself to drain otherwise I probably wouldnt have realized so soon what it was.