that depends on what you're asking. if you mean applying as someone who will have their degree by the time you enter dental school then there is no preference. but if you mean applying as someone who won't have their degree by the time they enroll in dental school then that's a different story.
i think every school prefers graduates over someone w/out a degree. if you have some stellar stats and great extra curriculars you could get accepted, but usually non-graduate acceptances go to people in unusual circumstances like non-traditional applicants that are older with families and working full time.