As I am now in the early part of my mid 50's and have been practicing for now over 25 years, and have numerous colleagues who I consider friends, who are in their late 50's and 60's (the age when many typically think is around "retirement time") the thing that I am noticing, even if money isn't an issue, is those that truly "retire" (as in don't practice dentistry anymore) are those that in the years/decades leading up to when they chose to retire, they had a robust life outside of their professional life as a dentist, and as such spent the time cultivating outside of dentistry passions and often also social networks, that keep their post dentistry retirement life full of enjoyment.
Those who can't ever seem to fully retire, often if one looks objectively at them, never really spent the time cultivating their life outiside of being a dentist, and as such really never had outside passions/social networks that wasn't dentistry based. They spent years and years with their lives so consumed by "being a dentist" that sometimes they end up with a life where they don't know any other way. For many, since they burn out eventually because they feel they can't see themselves as anything but a dentist, they tend to become somewhat crummudgeonly as they age, which makes finding other, outside of dentistry things to do and occupy themselves, difficult.
I would strongly suggest that as one goes through their career, even if their true passion in life is dentistry, that they also take ample amout of time to have a life outside of dentistry, that you actually enjoy as much, if not more, than being a dentist.
Personally I feel very confident, that when I decide that it's time to retire, that I have plenty of other interests outside of denistry, that I look forward to having more time to do, and not feel like my indentity will be lost. My hunch is that my business partner, who is about 10 years older than I am, will likely retire after I do, and it's not a $$ thing, simply because his life is basically defined by who he is as a dentist, even if he really isn't enjoying day to day dentistry a lot. He just doesn't know what to do with himself when he isn't in the office, and will often end up spending multiple hours per day, in our office, on his days off, even though he isn't seeing any patients.
Make sure that you have a life outside of being a dentist, to keep your life well rounded!