Schools like the idea of people helping others... That is why shadowing, volunteering and whatnot are looked favorably upon. However, the fact stands that dentistry a science based profession, so those applicants with exceptional scores will be readily welcomed to dental school.
Also, poor access to care is, as others have already noted, due to economic reasons. This is also because healthcare is a privilege, not a right. It is a cruel world, but it is still survival of the fittest - if you cannot afford care, you cannot get care. At its most basic level, healthcare is a service, and thus must be paid for. Its rough, but that's the way it is.