How long is dental school, if you have your bachelor's degree in US?

If you did not complete its pre-dental requirements, then you will have to return to school to do that. Depending on what BA / BS is, it could be up to 3 years of education just to get pre-dental. Then take the DAT. From there, you go to dental school, which is normally 4 years. Some states require a residency program and if you want to specialize, then you have to take additional work in that specialty.