It sounds like molar spurs, which grow outward from the back teeth into the rabbit’s cheeks. For most rabbits they are not a regular issue that needs human intervention because hay eating files down the spurs so they don’t harm the rabbit’s mouth, but with smaller breeds (dwarfs, mini lops), the structure of their face and sometimes including bad genes make them more susceptible to needing molar grindings occasionally.
Your rabbit is probably developing the crust from drool. If he’s increased his water intake, that also supports spurs because he’s trying to lubricate his mouth in order to lessen the discomfort. Moving his mouth around and chewing is potentially him moving around the spit to coat his back teeth.
My Wick has to have his teeth ground every 5weeks at the minimum because he cannot grind down the spurs on his own. He’s a Netherland dwarf blessed with a crooked jaw and an underbite, so his chewing motion does not allow all teeth to be ground down correctly. He’s been through seven grindings so far I believe, and he’s a tiny, 2lb teenager.
It can be scary to put a rabbit under for any procedure, but if you find a vet who is experienced specifically with grinding down spurs on a small rabbit, and your rabbit is generally of good health and can bounce back quickly, then there’s very little risk. Typically I set an appt at the 5 week mark, I go in with Wick, we confirm there’s bubbles in his mouth (sign of saliva) and they take him for 15minutes to do it and plop him in the lobby for me. Then we just stay there for about 10minutes while he wakes up and gets reoriented.
Wick is especially resilient, and every rabbit is different, but generally speaking molar grindings are a standard procedure that are pretty low risk. Some vets wait until the rabbit is showing signs of pain or is not eating due to the discomfort, but I never wait until that long because it just seems mean in a way, especially if you establish this is regular for your rabbit.
Also, your rabbit is 3yo, so it could just have taken a long time for them to form and you won’t need it again until 3yrs later. Alternatively, it could be a start of a regular regimen. It’s up to you to observe how he’s doing and reacting. So far I think k you’re doing a wonderful job.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.