I can verify this for you for UNC SOD. They look for underprivileged/underrepresented applicants such as applicants that are the first in their family to go to college, first to graduate high school, first to apply for professional school, etc.
In UNC's case and I'm sure for other schools such as Columbia, etc. that are trying to accept more underprivileged/underrepresented students, your background would be a disadvantage if that was the only variable taken into consideration for your application.
I'm sure that since you have relatives in the dental field, you know what you're getting into and you've busted your ass to get to this point. So I'm sure your credentials are stellar and you shouldn't need to worry about your background when it comes to relatives in the dental field 🙂