Depending on what you took in college, and how long ago that was, you have to have at least the pre req classes completed with excellent grades in them (optimally).
Bio 1 and 2 with labs
Chem 1 and 2 with labs
O Chem 1 and 2 with labs
Physics 1 and 2 with labs
Biochem (some schools)
A semester or 2 of English (some schools)
A semester or two of math/comp sci (some schools)
Then you have to take the DAT and earn competitive scores. You also have to put in shadowing/volunteer hours with dentists to show you really want to become a dentist. Finally, you're ready to apply.
It is indeed a lengthy process for non-trad people that never took the pre req courses, or who had sub par GPAs in undergrad. But, there's tons more information over on the pre-dent board.
