One of the LoRs that I'm waiting for AADSAS to receive is from the dentist I interned under, and I think arguably my most important one. He chose to send in a paper LoR, and I mailed him a packet with some info (resume, personal statement, thank you note). Over three weeks have passed, I've received two of my other LoRs (electronic), but none from him. Does it take a longer time to process paper LoRs? Is there a nice way I could contact him and ask him to hurry it up?