What is the ruling on the work of a female dentist whose work requires her to examine and treat men?

The fundamental principle is that a female doctor treats women of her own gender, unless there is no male suitable to treat men, or if necessity and need dictate otherwise. This is because her treatment of men involves viewing their private parts and touching, which is not permissible except out of necessity or a need that is considered equivalent to necessity. If a woman can treat a man without viewing forbidden private parts, touching, or being in seclusion, then there is no objection.