Is it obligatory for the questioner to research further the issue of a dentist using a cosmetic filling, after the dentist informed her that the cost of the filling is covered by insurance?

The phrase "the physician approved by the institution" means that the worker should not need a filling, and that their purpose is not merely cosmetic, but rather for therapeutic necessity. There is no harm in submitting the treatment report to the institution according to what the physician has clarified, while disregarding obsessive thoughts and doubts.