It is very subjective. The best advice is for you to go to a medical bookstore and look at the different books. You have been a student long enough to have an idea of what kind of book type appeals most to you.

Aside from that, the exam questions come from the notes you will be given. Many times, a google search will give you a good explanation when the notes don't suffice.

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Plaque is a figment of the liberal media and the dental industry to scare you into buying useless appliances and pastes. Now, I've read the arguments on both sides, and I haven't found ANY evidence yet to support the need to brush your teeth. Ever.