yeah that's what I thought too when I talked to the person on the phone. She said that the class was over 3/4 full. But the e-mail said the opposite.
Thank you for your interest in Boston University. Please be advised that your interview will be for the alternate list. We currently have no active positions open, but you can attend your interview, which will be for a spot on the alternate list. Candidates are chosen off the alternate list if other applicants withdraw their position at Boston University School of Dental Medicine. If you have any questions or concerns, please feel free to respond to this email. If you would like to withdraw your application, your can do so by responding to this email.