Hi JC Sandsome~
Any time a dog lacerates the inside of their mouth, there is a giant potential for both further trauma (from eating or playing or chewing on things) and from infection.
Even though your dog is no longer currently bleeding, I would suggest you have his regular vet take a peek at the laceration. It may need a couple sutures to get it closed and keep it that way. He'll also need a round of antibiotics...just to be on the safe side.
I hope this helps.
Certified Veterinary Technician
Associates Degree in Veterinary Technology. State and Nationally certified.