Is he neutered? If so, does he have company in the form of another neutered bunny?
How big is his hutch? How often does he come out for a run?
Does he have toys? Does he have any wooden sticks or other things he can chew on? Does he eat a lot of hay?
Is there anything to suggest he might have a tooth problem (signs such as dribbling, chewing slowly or losing interest in certain foods, eye troubles, losing weight, amongst others)?
Just various things to consider when trying to answer your question so if you could provide a bit more information we may be able to give advice.