Thank you Tony,
I have to say I am very worried about Fang. As I noted before, this is grossly abnormal for a hamster and suggests severe issue. In this situation, if he was fine until after your son played with him, I'd be very worried that he has been dropped or experienced some trauma. Otherwise, especially if he hadn't been eating prior to this and was collapsed before they played, I have to say that the labored breathing makes me concerned that his teeth were not the only issue that was bothering him. And it is worth noting that a lack of appetite is common non-specific issue of the unwell hamster. But labored breathing is going to be telling us that we either have a primary lung issue, heart issue, or that his lack of appetite and systemic disease (ie tumor, organ based, infection, etc) has caused metabolic instability such to lead him into metabolic decompensation.
Now if you wish we can discuss supportive care with food, fluids, warmth but to be honest with you, I am concerned that Fang sounds to be dying on you. I know he was just seen, but in this state he is likely showing a completely different picture to what he showed the vet. His current state sounds like he is deteriorating into a state of collapse, respiratory distress and that he is just too poorly to even try and do anything he would normally do. And in the wake of these signs, I must warn you that he is going to have a guarded prognosis here. Therefore, it would be ideal to have him seen urgently, to see if there is any help that can be given or to even consider putting him to sleep to avoid further deterioration and death.
So, in this situation, we have a wee hamster in a dire state. If you wish to discuss supportive care measures, then let me know. But if he is struggling to breathe, I do have to warn that the stress of handling and increased risk of aspiration when syringing food and fluids are very significant and could cause him to arrest. Therefore, the truly best course of action would be to have him seen again and reassessed. If he is as collapsed as you have noted, then I do suspect he is in a terminal state of something more serious then his teeth and that euthanasia may be kindest for him.Finally, just to note in case you were keen to have him seen today, some veterinary practices in our country have Sunday office hours (ie my practice is open 9-5 today on Easter Sunday). As well, I wanted to mention that most veterinary practices here do have contingency plans for emergency care for their patients even when they are not open. Therefore, it is worth ringing the practice. If they are open, you can get him seen today. If they aren't, then they will likely have a message to direct you on how to contact their out of hours service. And if you don't have a vet you can find one local to you, you can check you can check the RCVS Register (HERE) to find your local Vets Now (LINK) who are open all nights/weekends. In any case, if you wanted to get him checked out sooner then there are options to have him seen today too.
Please take care,