Dentist removed crown and put medication on root.no infection in root. but another dentist who saw me suggested it better to leave to leave root open?

Never leave open: I never recommend leaving a root canal open especially if there is no infection. Left open you could expect tooth and jaw infection to soon follow.

If no infection...: ... leave it closed with the medication and temporary filling. If infected and painful and pus coming out of the tooth, leave it open until antibiotics have controlled the infection.