I agree - this is an issue a vet has to see because it can be caused by several different things. It might be something that can be easily treated with antibiotics and painkillers or it might be more serious and a vet will be able to tell you. Sorry I don't know which country you are from so I don't know how easy it is for you to find a vet. If you can put your country in the location (or county if in the UK) someone nearer to you might have a local recommendation? BTW does he have a friend he lives with that might have been fighting with him?
It looks like he's been accidentally biting himself because of his tooth issue so don't put off the vet visit as you might be getting this in the early stages. If those little cuts get infected things could get very sore, and if he's not biting properly with the front teeth it can start to affect the back teeth - generally speaking back teeth issues are more difficult to correct. If you offer him the mushed pellets or recovery food slurry on a plate he might be able to eat it himself so try this before you start with the syringe. If he won't eat it and you have to syringe be gentle around those front teeth because I bet they are a bit tender at the minute. You can try to slide the syringe into one side of the mouth around those front teeth.
People on the forum have had piggies which had to have front teeth trimmed (they grow back all the time) or even removed, and piggy can learn to manage without some of the incisors so this wouldn't be a disaster. It can take a little time for them to learn how to get the food into their mouth but it's the back teeth that do all the chewing and grinding. Veggies can be cut into little strips to make them easier to get in. When my girl started to drop veggies from her mouth it was because she had pain when biting, but when I cut the veg into spaghetti-like strips she could tuck in.
Good luck little Bandit - you are very sweet and we love you and your special teeth already x