Which one are you looking it?
I know of perio, endo, and pedo specialty residents that had 10+ years of experience.
That being said, you may hate being back in residency. You will have superiors that may or may not have huge egos and you will have academic BS to deal with in any residency that you definitely don't have to in private practice. On the flip side, you don't have to worry about staffing and management etc (though you do have to deal with the consequences of an untrained/no show assistants) so just be aware of that.