I graduated in 2001 and I will be starting dental school in the fall (Temple). Although I graduated 5 years ago, I went back to school and did a post-bac program to increase my science gpa (I took upper level science courses). In fact, schools that I spoke with did not like if you repeated any science courses.
I can only speak about two schools in particular (Temple and Columbia). I spoke to admissions deans at both Temple and Columbia about my application at different points in the admission process. When I mentioned in conversation that I graduated several years ago from undergrad, they both said it didn't matter. As many people have stated before on the forum, a strong DAT score and high GPA are really the two major criteria in the admission process (or at least in the beginning of the process to select individuals for an interview).
I would suggest that if you graduated several years ago, you may want to send an email to the admissions staff at various schools. You may want to ask them if they also want to see any additional courses since you graduated from college, etc.