Each program differs.
We require passing scores on National Boards, and passing in dental school.
We then compare the grades with the letters of recommendations and select the best to interview.
Acceptance is often based on the interview and what else the person has done - i.e. extracurriculat work/research/volunteerism/hardships
Many programs look at grades only.
We try to blend our program from different schools and try to get 10 residents who can function as a team.
This year we have residents from 6 universities, next year its 4... each year is different.