Berlusconi parties were systematic prostitution -prosecution

* Prosecution says "bunga bunga" parties involved prostitution

* Berlusconi and "Ruby", then a teenager, deny they had sex

* Media magnate's dental hygienist accused of prostitution

By Sara Rossi

MILAN, March 4 (Reuters) - Parties at Silvio Berlusconi's Milan villa were arranged for prostitution and were not the elegant dinners he suggested, the prosecution in the Italian media magnate's sex trial said on Monday.

Making closing arguments in Berlusconi's trial on charges of having sex with an underage prostitute, prosecutor Antonio Sangermano said the parties involved dinner, erotic "bunga bunga" dancing and then sex between aspiring women TV presenters and invited guests.

Berlusconi denies charges that he paid for sex with Moroccan nightclub dancer Karima El Mahroug when she was 17 and then abused his power as prime minister to get her released from Milan's police headquarters, where she was held on suspicion of theft in May 2010.

Mahroug, a teenage runaway widely known under her stage name of "Ruby the Heartstealer" also denies having sex with Berlusconi, 76, at the parties in his villa or elsewhere.

Sangermano accused former Lombardy regional councillor Nicole Minetti, once Berlusconi's dental hygienist, of taking part in acts of prostitution and inducing others to do so.

Minetti is on trial separately - with Emilio Fede, a former senior journalist in Berlusconi's media empire, and show business talent scout Lele Mora - on charges of procurement.

Berlusconi faces up to 15 years in jail if convicted although nothing will be final until two appeals allowed by Italian law, usually a lengthy process.

The verdict in the Ruby trial is expected on March 18 and Berlusconi faces judgment in two other trials this month, one for tax fraud and the other for making public the taped contents of a confidential phone call.

His legal troubles deepened last week when prosecutors revealed he was under investigation for bribing a senator to change sides in parliament in 2006.

Scandal around Berlusconi has increased the reluctance of other parties to cooperate with him in parliament after last week's inconclusive election, despite his remarkable performance in taking his centre-right group from close to disintegration last autumn into second place in the vote.

Berlusconi's lawyer, Niccolo Ghedini, said the prosecution's summing up was "exquisitely one-sided". (Writing by Barry Moody; Editing by Louise Ireland)