Charlie Sheen Investigated for Pulling Knife On Dentist

Charlie's lawyer Marty Singer calls the allegations "completely fabricated." He adds, "No bodyguard made the absurd statement to the dentist. Charlie had a bad reaction to the noxious gas put in his mouth and nose."

Charlie Sheen clearly doesn't like going to the dentist, because he's under investigation for assault with a deadly weapon for allegedly going nuts in a dental chair in a rock cocaine-fueled rage ... TMZ has learned.

Law enforcement sources tell us ... Charlie was at an L.A. dental office last Thursday for an abscess. He sat in the chair as the dental technician placed a mask over his face to administer nitrous oxide, when she says Charlie went insane ... flailing his arms and striking her.

The technician told cops she walked out of the room as Charlie's security guard entered. Charlie's personal dentist was there along with the oral surgeon. There was a lot of commotion and the technician says when Charlie's dentist finally came out he told her Charlie pulled a knife and went after him. The dentist wasn't hurt.

The technician also told cops the bodyguard told the dentist Charlie was high on rock cocaine.

We're told there's an active LAPD investigation and cops are looking at a possible battery against the technician and felony assault with a deadly weapon for the alleged knife attack on the dentist.

We're told cops want to interview Charlie and the dentist before sending the case over to the L.A. County D.A., who will decide whether to prosecute.

We reached out to Charlie ... so far, nothing back.