For each alleged victim's account in court yesterday of a traumatic sexual assault at the hands of a South Hills oral surgeon, his defense attorney had an answer.

Instead of groping a victim, could the doctor have been merely removing a heart monitor?

Rather than placing a victim's hand on his genitals, could he have been taking her blood pressure?

Could the heavily sedated minds of 17 women have created experiences that weren't real?

The trial of Robert John Boyda Jr., 44, of Mt. Lebanon, began yesterday with defense attorney William H. Difenderfer asking those questions in an attempt to undercut the accusers.

Four women told Common Pleas Judge Anthony M. Mariani, who is presiding over the nonjury trial, that they were assaulted while coming out of anesthesia.

The women -- ranging in age from 23 to 59 -- testified to similar experiences. They said they awoke, groggy, in a recovery room to find Dr. Boyda sexually assaulting them in some way, but they felt paralyzed or weakened by the drugs and drifted back into unconsciousness without putting up a fight.

"Was it a dream?" Deputy District Attorney Janet Necessary asked a 29-year-old nurse.

"Absolutely not," the woman replied.

The Post-Gazette does not identify victims or accusers of sexual assault.

Yet in his opening statement, Mr. Difenderfer said that each accusation was, in fact, a dream.

"In every single case, the patient has post-incident amnesia," Mr. Difenderfer said. "Amnesia is not convenient. It doesn't come and go."

Wielding dental implements and using a blackboard to break down stages of unconsciousness, Mr. Difenderfer gave a lengthy lecture on the practice of anesthesia during his opening statement.

Among the drugs in the cocktail Dr. Boyda typically administered to general anesthesia patients is propofol, which in rare cases has been known to cause vivid sexual dreams.

Mr. Difenderfer said that drug was the likely source of the allegations and he will present evidence that during a time span when Dr. Boyda was not administering propofol, there is a gap in the alleged assaults.

Also, he said, Dr. Boyda never used a paralyzing agent on his patients.

"All of them had the ability to move and fight and strike and, quite frankly, get up and walk out," Mr. Difenderfer said.

The defense attorney also called the accusers' timing and motives into question. Three alleged victims initially came forward to police with the allegations and the rest contacted authorities after Dr. Boyda's January 2008 arrest and subsequent news media attention. One of the women who testified yesterday has taken steps toward filing a civil action against Dr. Boyda.

Mr. Difenderfer said he will call expert witnesses to testify about the effects of anesthesia as well as former assistants of Dr. Boyda, who will testify that they were present at the time of some of the alleged attacks.

Ms. Necessary said she will call two former assistants of Dr. Boyda who will say they saw him in compromising positions with other patients whom he is not charged with assaulting. There were 20 separate cases against Dr. Boyda, but three of those cases were dropped yesterday because the statute of limitations had passed.

And in the face of theories to the contrary, the four alleged victims stuck to their stories yesterday that the Harvard-educated father of three attacked them at their most vulnerable.

"I'm still upset about it," said a 23-year-old accuser.