First, the BU thing:
Have you called the admissions office at BU?
Tufts:
Nearly all dental schools participate in the AADSAS application system. Therefore, in order for Tufts to receive your LORs, you would need to fill out an application on AADSAS. In the application, there is a section for evaluations to be added. Your evaluator (person writing LOR) will be prompted to electronically submitt the LOR to AADSAS once you have entered their info into that section of the application.
Hope this helps. And remember; when all else fails, read the instructions.