If you're interested in specializing it may be more difficult not being ranked. It's not uncommon for UCLA ortho applicants to apply to 20-30 programs. I'm sure it's hard enough for ortho programs to rank their interviewees. Without a class rank it likely becomes difficult to justify choosing a non-ranked student over a highly ranked student. As far as competitiveness in the class(I can only speak for my own school), dental school offers a fairly cooperative atmosphere. I'm sure there are a few gunners out there in the country, but I doubt they would change their ways in a non-ranked program.