I think you should ask for letter of Rec from any professor you can. Be sure that the professor like you or that you had an A in the course.
You don?t want a letter saying,
XX got an A in the course like have of the other students. I really can not judge if XX is a qualified dental school applicatant based on this performance.
Some thing like that. It is good to get a letter from professor that know you personally. If they do not, provide them with personal statement, DAT scores, Activities in college, and transcribes to give them information to write about other then your preformace in class.
Based no my experience, I suggest getting LOR from Biology, Chem, Upper division sci, non-sic, dentist, employer, and possible a minister for private schools (Loma Linda).