Can I be denied a green card since my case was expunged?

Yes, you can be denied. Expungement does not help you for immigration purposes.

More information is needed, but you must disclose the arrest. If you pled guilty, facts were presented on the record or other irregularities appear on the criminal record, then this complicates matters. Not having a certified copy of the record to confirm the dismissal may cause a denial because you may no longer be able to obtain such a record after expungement. The adjustment interview can get confrontational, so you should consider hiring a competent immigration attorney to discuss the situation and suggest what evidence must be presented at the interview. Otherwise, the applications may be delayed or denied. Again, I strongly recommend an appointment with a competent and experienced immigration attorney, who can review all of the facts. The above is general information, not legal advice, and does not create an attorney client relationship.