Health insurance group Achmea is attempting to reclaim €4m from over 1,000 dentists after it paid invoices which were either ‘impossible’ or fraudulent.

In total, the insurer believes it has paid out up to €4m in invoices which were incorrect between 2010 and 2012. The claims follow an analysis of thousands of bills, some of which show ‘impossible’ treatment combinations, the insurer said.

Some 250 dentists received a letter about the claims on Thursday. The rest will follow later. The Netherlands has some 8,000 registered dentists, meaning one in eight has sent out wrong invoices.

Achmea said it does not believe all the cases involve deliberate manipulation of the invoices and pointed out that dentists work with old IT systems, making invoicing more difficult. The sums involved range from a few hundred to thousands of euros.

The Dutch health authority NZa said in December that health insurance companies should do more to track down fraud. This followed publication of a report which claimed doctors, dentists, psychologists and pharmacists were being wrongly paid a total of €75m a year due to incorrect or fraudulent invoicing.