My understanding is that the earlier you apply, the greater your chances. Dental schools, participating in AADSAS, do not begin to notify of admission until December 1 - at which time, every seat is available. As the cycle moves along, available seats are confirmed and therefore, fewer seats are available as the application pool continues to grow until it is officially closed (application deadlines vary between dental schools).
In my opinion, if schools review applications in the order they are received, of course chances of serious consideration are greater earlier in the cycle. However, I would find it difficult to believe that July, August, or September would be considered "late." 🙂