Is he in or out of network?

They had the wrong dentist in the claim that was sent over who was out of network. The correct dentist is in-network.

I was told by a village doc that the system hires high school drop outs to code after they coded a procedure that was never done. Now, since the fraud has been exposed, it is by design. Had I not questioned the bill, it would have been paid.

I have the same plan, had 2 implants that included crowns. Since that crown was attached to an abutment UHC denied paying anything

Did you appeal???

The $5,000 is the Annual Maximum for Dental. The percentage covered for each type of service is explained in your contract or paperwork.

And here is a classic example of confirmation bias. The problem the OP had was not due to UHC denying care which should have been covered. They apparently followed the rules. The mistake was made by the dentist's office which submitted the wrong codes for it to be covered. Place the blame where it clearly belongs.

United Healthcare continues to have the worst reputation of all the crooks that run all the so-called "Healthcare services". Scum!

Is your dentist listed as an in-network dentist. If not UHC only pays a portion.
If he is listed check to see what procedure code the dentist use. A listing of codes can be googled. Wrong code have dentist resubmit. Correct code file an appeal with UHC in writing and send certified mail return receipt requested. Follow instructions carefully for the documentation required. Call their customer service afterwards every 2 months for updates.
I initially got denied a replacement on 20yr old crown on a back molar that had broken claiming it was a cosmetic procedure. Took me 10 months but got crown fully paid.

Not disagreeing, and I am guilty as well in this case. However, time wasted, and patient time wasting for sloppy work for a patient and a customer who probably wasn't the first UHC dental customer is a sign of UHCs very low reimbursement rates. . . They did start a contract renewal negotiation with coachk's hospital at less than medicare reimbursement rates. I will be interested to see the final outcome, and will concede my confirmation bias as well. .

Is your dentist in the United network? If your dentist isn’t in the United provider network, you pay the difference between the United allowable charge and what your dentist charges. If your dentist is in the network they’ve agreed to the allowable charge.

Source?
Define "his cost".
Do you know what his overhead is?
What is "fair" for his time?

Crowns placed on implant abutments are considered implant services, not general restorative. If your plan does not cover implant services, it is not unreasonable to have this type of exclusion. Some better plans might cover that, but not most.