Given he has dental problems, Im guessing this could be because he’s drooling. Since he has recently seen the vet, perhaps you can call them and report the latest development? I read in your other thread that he had finished the meds he was on. Was this for pain relief? Have you noticed the wet chin since he stopped the meds? The vet could give some more if they think it would help.
My other thought is: could he be dipping his chin in the water to soothe his mouth? Or drinking more then usual? Does he have any difficulty drinking?
I wonder if you could give him a sipper bottle but keep the bowl of water also. If he is curious enough, he might give the bottle a try… If he takes to drinking from that instead, that could help dry the fur if it is getting wet just from the water. If it is drooling, he will most likely need to be seen again, Im afraid.
The fur/skin can get a bit smelly. It did for my rabbit that had dental problems. Some of his fur came away there also. If it’s drool, it can be just that making it smell but when the fur is constantly wet, they can develop a bacterial infection & “moist dermatitis” on the skin which contributes to smell also.