@Dave ***
depends on where you live
In Au I had to do the following
Written quote from OS dentist with details and itemised prices in the currency of your own country.
Letter from your Dr in own country stating why you are choosing OS option due to costs and availability waiting time etc
I went for early medical release request from my super. Once I had everything as they requested it was all sorted out with no issues.
This is only what I wanted to do but everyone’s situation is different to their needs.