It's a very good domain, but has both strong points and weak points. If you type 'dentalcenter.com' in its entirety into Google, you'll see that it is indeed a very common pairing... after 20 pages of top-to-bottom search results of dental centers ALL ending in dentalcenter, I stopped looking. You'll see that it is a very common - in fact pretty much the accepted - term.
That being said, it also makes it a bit of a hard sell, because most companies really want a descriptive term in there as well, like Hillside Dental Center or Jimbob's Dental Center or WhiterTeeth Dental Center, etc, to describe either the area or the owners or even just the image they want to portray. Just 'dental center' has no descriptive term.
Also, though they charge a lot of moolah, dental centers also have high costs of equipment, employees, insurance, etc. It's going to take a very large and lucrative one to buy this domain for a hefty price... and as I mentioned, most of them want a more branded approach with a descriptive keyword. Might get a buyer from among the many large dental centers out there, might not. Seems like a domain that would sell better to someone who has an online business rather than a real world tooth business, because it's more generic and it's ideal for a store. Hard to call this one.
But definitely has strong value, just depends who comes knocking with an offer. A large center, or perhaps a chain of them, might like to rebrand to this because it's definitive. I'd look for centers that have at least a handful of satellite clinics within a large city or county, and outbound email them. And I'd email any website that has an electronic dental biz, like selling equipment, machines, supplies, books, etc, a manufacturer or retailer might really like to rebrand to this. Look at any large dental equipment manufacture on Alibaba and email them too.
Wide swing in valuation; reseller price anywhere in the mid x,xxx at least; end user anywhere in the five figures (Hey, do you think if one of the 'big' domainers had this, they wouldn't get at least that much with all their leads/know-how?). A sober price would be low xx,xxx. With the right buyer and the right negotiation, might get that to mid xx,xxx or better.
My valuation is for the domain alone. I know you've done a lot with it, so of course having a lot of content, links, leads, traffic etc will drive that price up considerably, but I'm not going to try figure all that out for you
Good luck, nice domain