Very long story somewhat short

My mom went to her dentist to take care of a painful tooth and he
determined she needed a crown.  She had dental insurance which has
since ended.  The dentist started work and put in a temp and waited for
the crown to be made.  Meanwhile there was something wrong with the
insurance which took a few months to resolve.  The dentist kept pushing
my mom to take care of the problem so he could finish the work.

Eventually, the insurance came through and sent the dentist the check
to cover the crown work.  Meanwhile, the temp my mom had fell out and
she spent months in pain and with bad breath.  Infection?  The dentist
wouldn't take care of it until the insurance company came through.

Anyhow, upon receiving the check, the dentist refused to finish the
crown.  When my mom went down to the office to schedule an appointment
to finish the crown, the dental office tried to get her to pay over the
remaining $40 she "owed" (she had already paid $290 months earlier).
When my mom said she would pay after the crown was put in, the office
told her there would be no crown since her teeth had "moved" and too
much time had passed.  They would give her back the $290 and she would
have to scram.  All this after receiving payment from the insurance
company!

My brother will go down to the office today to have a talk with them.
If this doesn't resolve the issue, I'm advising my brother (I'm three
thousand miles away) to notify the insurance company, the local and
state dental board. Is there anything else we can do?  After all this,
I sure do not want this dentist to work on my mom's teeth, is there a
way to go to another dentist and have it covered?

This dental office services mainly an immigrant clientele and I think
this is not the first they've pulled stuff like this.  They can get
away with it because many of their patients do not have the financial
and language wherewithal to fight back.