Dubbed the "horror dentist" by the media, Mark van Nierop, 50, claims to suffer from "psychological problems" including gender identity issues and suicidal tendencies, which he had cited in a failed attempt to challenge his extradition from the Netherlands.
Van Nierop was detained in Canada in October and flown back to the Netherlands where he was arrested under a Paris-issued international warrant and a court approved his extradition last month.
French investigating judges Thursday night ordered him to be sent to a prison psychiatric unit in the Loiret department, south of Paris, after new complaints were filed against him.
Many of Van Nierop's 2,800 patients suffered disorders ranging from sepsis to broken jaws, according to a French victims' group.
Dutch media also reported healthy teeth being pulled for no reason and abusive billing.
A group of 120 French victims formed a collective to press charges and a criminal investigation was opened in May 2013.
But Van Nierop fled in December, forcing French authorities to seek an international warrant for his arrest.
He was finally detained in the small town of Nackawic in the Canadian province of New Brunswick.
Dutch prosecutors are also probing his claim that he killed his second wife in 2006, two years before he was persuaded by an investor to move to the remote rural area of Chateau-Chinon in central France, described as a "medical desert" because of a lack of healthcare professionals.