Jacobus van Nierop, 51, is on trial for ripping out healthy teeth and leaving patients with injuries including broken jaws, recurrent abscesses and septicaemia in the small central town of Chateau-Chinon.
In this case, “we see nothing but greed, indifference to others, even pleasure at causing pain,” said prosecutor Lucile Jaillon-Bru.
She told the trial in Nevers that Van Nierop had carried out “useless and painful procedures” on about 100 patients with the aim of having them reimbursed by medical insurance schemes.
Jaillon-Bru described him as “a man who doesn't take responsiblity for anything”.
Van Nierop, who called himself Mark, was hired by a head-hunter and was initially welcomed by locals into an area which was lacking in medical services.
Giving evidence in court, a neighbour recalled the arrival of a smiley, larger-than-life character, with a “big 4×4, a big dog, a big cigar”.
But by 2011, the authorities were starting to question some of his accounting practices, and patients were starting to compare notes on his dentistry.
The court heard nightmarish tales, including one from Sylviane Boulesteix, 65, who saw Van Nierop in March 2012 to have braces fitted.
“He gave me seven or eight injections, and pulled out eight teeth in one go. I was gushing blood for three days,” she said.
Around 120 former patients joined a victims' group set up in early 2013.
The trial has heard conflicting expert opinion about Van Nierop's psychological state.
One psychiatrist found he had “narcissistic tendencies” and was therefore incapable of making a moral judgement of his own actions.
But another found he was “perfectly aware of what he was doing”.
Although he is not required to offer a plea under French law, Van Nierop has sought to deflect responsibility, saying he suffers from “psychological problems” including gender identity issues and suicidal tendencies.
Van Nierop himself said: “I was not in the right state to put myself in my patients' position.”
He was arrested in June 2013, but fled France while awaiting trial. He was later tracked down to a small town in Canada, arrested and extradited first to the Netherlands and then to France.