Italy's former Prime Minister Silvio Berlusconi.

Milan - Silvio Berlusconi's former dental hygienist and the son of Northern League founder Umberto Bossi are among 40 politicians under investigation for allegedly using public funds for personal expenses, judicial sources said on Friday.

The inquiry is one of a string of embezzlement investigations involving local government politicians that have further damaged the image of the already widely distrusted political class ahead of an election early next year.

The scandal also risks damaging Berlusconi's centre-right People of Freedom (PDL) party and its former ally, the Northern League, which are already lagging in opinion polls.

Judicial sources said Nicole Minetti, who was Berlusconi's dental hygienist before becoming a member of the Lombardy regional council, was among those under investigation for allegedly using public funds for personal expenses.

In Minetti's case, these included 832 euros ($1,100) for a night at a Milan hotel, several dinners in expensive restaurants and an iPad, the sources said. Minetti is already on trial in Milan for allegedly procuring prostitutes for Berlusconi's sex parties, a charge she denies.

She was not immediately available for comment.

Renzo Bossi, son of the former Northern League leader Umberto Bossi, is also under investigation, together with other League and PDL politicians. The investigation involves expenses by politicians between 2008 and 2012.

The embezzlement scandal, together with the arrest this year of a member of the regional government for allegedly buying votes from the Calabrian mafia, has led to the local legislature being dissolved in October.

Voters in Lombardy, Italy's richest and most populous region, will likely go to the polls to pick a new regional administration on the same day of the national election, now expected in February.

A Northern League statement said anyone found at fault by the investigation would have “to reimburse all the money with the interest”.

The central region of Lazio will also vote in a snap election early next year after its own centre-right local government collapsed over a similar embezzlement scandal.

The wave of corruption probes has helped boost support for the anti-establishment, populist Five Star Movement led by comedian Beppe Grillo, which surveys say is now the second biggest political force behind the centre-left Democratic Party. - Reuters