There is a key post above on claiming back tax on medical and dental expenses,
which you should read. It lists the dental treatments which you can claim for.
According to citizensinformation, there is no mention that only medical expenses incurred in Ireland, are suitable for tax credits.
However, I don't know of anyone who has done this.
As the tax credit for you would be 800 euro, I would suggest that you pursue it,
and please let us know how you get on.
If I were you, I would ask the Dentist to fill in the Med2 form, and ring Revenue and
ask them for an answer.