Is it permissible for a dentist to write down a different treatment procedure than what was performed for the patient (such as extraction or fillings) in order to obtain the approval of the insurance company to cover the cost of an uncovered treatment (such as prosthetics), sometimes at the patient's request?

Commercial insurance is forbidden, and it is not permissible to benefit from it except to the extent of what was paid. As for cooperative insurance, it is permissible. It is not permissible for a doctor to write a report for more than what the patient actually needs in cooperative insurance, because it is a breach of contracts, and is deceit and falsehood forbidden by Islamic law. As for commercial insurance, it is permissible for the insured to recover what he paid in premiums by any means if he finds no other.