The dentist, who fled to Canada after being questioned by French police, is described as a “real brute” by one former patient.
A dentist nicknamed “the butcher” by French media has appeared in court accused of mutilating more than 100 patients.
Jacobus Marinus (Mark) van Nierop arrived in a police car, his head covered by a blanket, in Nevers, near the town of Chateau-Chinon, where he began practising in 2008.
The 51-year-old faces charges of defrauding French social security and “wilful violence causing mutilation and permanent injury”.
Many former patients attended the opening of the trial, where they described their experiences at the hands of van Nierop.
One said he had “ruined” her life after she had gone to have her teeth cleaned.
Danielle Wezemael said: “He filed my teeth down so I had to use my palate to chew.”
Another former patient Nicole Martin said: “When I was on his chair he was a real brute.
“I have since seen other dentists who were gentle, who had the technical means which means that today when you go to the dentist’s you don’t suffer any longer – but it is certain that he had no compassion … he would carry on pulling out teeth.”
Geraldine Letot said she had had to undergo extensive dental work after seeing van Nierop, including having teeth removed.
“I have pain, pain that I had never experienced before and which I should never have had,” she said outside the court.
Van Nierop, who is originally from the Netherlands, disappeared after being questioned by French police in 2013.
He was arrested the following year in New Brunswick, Canada.
Van Nierop claimed at the time he was suffering from psychological problems and confusion about his sexual identity.
In January this year, his lawyer Delphine Morin-Meneghel was quoted as saying he “recognised that he did not do good work” but “was not the horrible person some people had described”.
His flight to Canada was part of a plan to take his own life, she said, adding that he was in poor health.