I feel for the OP.
When my kids were children the dental plan we had specifically covered braces. And paid almost everything. Though only one of my three kids needed them.
When I retired I kept my health insurance fully paid but could not keep the dental plan. Not even if I offered to pay for it out if pocket.
I started a second career and the dental plan stinks! I’m constantly fighting with them to pay stuff. Now they want a co-pay for 6 month check ups.
If a crown breaks or comes off during the first 5 years they’ll pay to fix it. If it breaks or comes off after 10 years they will pay to replace it. If it breaks or comes off between 5 and 10 years they won’t pay a dime. It’s weird!
My only advice is to keep hounding them. That’s the only thing that has worked for me.