Is it permissible for a man to be treated by a female dentist if a competent male dentist is unavailable, given the presence of a female dentist who is praised and causes no pain, while the male dentist is criticized for frequently harming patients?

As long as you can find a skilled male doctor to treat you, it is not permissible for you to go to a female doctor. We do not believe that you will be without a skilled male doctor in your country. And assuming there is no male doctor other than this one, the slight pain, which is not unusual for such a condition, we do not consider it an excuse for you to abandon him and go to a female doctor.