A Sydney dentist is accused of sexually assaulting multiple patients, including a 15-year-old and another who wore her school uniform to her appointment.

An aroused Bassem Fouad would frequently press himself against his patients, prosecutor Daniel Noll alleges.

Fouad would also place his dentistry tools on their breasts, the prosecutor told Downing Centre District Court during the trial's opening on Tuesday.

He is charged with nine counts of aggravated sexual touching, indecent assault under authority, and intentionally sexually touching a child.

He has pleaded not guilty to all charges.

The 55-year-old operated at two dental clinics at Mascot where the alleged assaults took place.

The five women cannot be named for legal reasons.

"It's not pain you can feel, it's just pressure," the accused allegedly said to one patient who felt his crotch area against her head.

Mr Noll told the jury one woman said she felt something "round like a sausage" moving side to side against her arm.

Another patient, who was 15 at the time, said she had to slide down the dental chair to avoid Fouad, who began thrusting himself against her head.

Two reports were made to police in 2016 and 2021. Fouad denied the accusation each time.

Mr Noll told the court CCTV footage captured in 2021 showed the dentist regularly touching his groin and the breast of a patient on one occasion.

The footage also showed Fouad removing his gloves and taking his penis out of his pants.

Mr Noll said the dentist explained to police he took his penis out because he suffered a groin infection.

The defence will present its case on Wednesday.