Hi there,
How many pellets are you giving him? Also, celery and pears are not great for bunnies. Celery alone doesn’t have much nutrition, and pears are very high sugar and should only be an occasional treat.
In the bunny’s mind, pellets are like ice cream to a kid, and the hay is healthy food. If they can fill up on pellets, they won’t want to eat their hay. Adult buns only need a small amount of pellets each day (a couple tablespoons usually).
So if his teeth are cleared by the vet, I would stop the celery and pear, and reduce the pellets (if you give his weight we can suggest how much to feed, but it I can almost guarantee won’t be more than a 1/4 cup a day). I’m guessing he will start eating more hay!
Then you can start introducing more nutritious veggies (slowly, no more than 1 new veggie a week). Romain lettuce, cilantro, and dandelion greens are good ones to try. 
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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.