A Staten Island man on parole after 20 years behind bars for killing his wife planned to rub out his ex-girlfriend over a $5,000 loan for dental work, cops said yesterday.

On Thursday night — 21 years to the day that his wife was found fatally shot — Charles Baeza, 72, was busted at Larocca’s Pizzeria in Dongan Hills after allegedly trying to purchase a handgun and silencer for $300.

He pleaded not guilty and claimed in court that when he told an undercover cop that he wanted to kill his 52-year-old ex, “It was just a joke.”

Baeza, a Dollar Tree store clerk who murdered his wife, Ruth, in 1990, is due back in court Aug. 24.