TULSA, Oklahoma (AP) - Hundreds of patients of an Oklahoma oral surgeon accused of unsanitary practices showed up at a health clinic Saturday, looking to find out whether they were exposed to hepatitis or the virus that causes Aids.

Letters began going out Friday to 7,000 patients who had seen Dr. W. Scott Harrington during the past six years, warning them that poor hygiene at his clinics created a public health hazard.

The one-page letter provided information on how and where to seek treatment but couldn't explain why Harrington's allegedly unsafe practices went on for so long.

Testing for hepatitis B, hepatitis C and the virus that causes Aids began at 10am on Saturday (11pm, Singapore time), but many arrived early and stood through torrential downpours.

The Tulsa Health Department said 420 people were tested on Saturday at its North Regional Health and Wellness Centre. Screenings resume on Monday morning.

Ms Kari Childress, 38, showed up at 8.30am, mainly because she was nervous.

"I just hope I don't have anything," said Ms Childress, who had a tooth extracted at one of Harrington's two clinics five months ago.

"You trust and believe in doctors to follow the rules, and that's the scariest part."

Inspectors found a number of problems at the doctor's clinics in Tulsa and suburban Owasso, according to the state Dentistry Board, which filed a 17-count complaint against Harrington pending an April 19 license revocation hearing.

According to the complaint, needles were reinserted into drug vials after being used on patients, expired drugs were found in a medicine cabinet and dental assistants administered sedatives to patients, rather than the doctor.

One patient, Mr Orville Marshall, said he didn't meet Harrington until after he had two wisdom teeth pulled about five years ago at the Owasso clinic.

A nurse inserted the IV for his anesthesia; Harrington was there when Mr Marshall came to.

"It's just really scary. It makes you doubt the whole system, especially with how good his place looked," said Mr Marshall, 37.

An instrument set reserved for use on patients with infectious diseases was rusty, preventing its effective sterilisation, and the office autoclave - a pressurised cleaner - was used improperly and hadn't been certified as effective in at least six years, according to the complaint.

Dr Matt Messina, a Cleveland dentist and a consumer adviser for the American Dental Association, said creating a safe and hygienic environment is "one of the fundamental requirements" before any dental procedure can be performed.

"It's not hard. It just takes effort," he said.

An average dental practice can expect to pay more than US$40,000 a year in equipment, tools and supplies alone, according to several dental organisations.

Attempts to reach Harrington have been unsuccessful.

No one answered the door on Thursday at his Oklahoma home, which property records show is worth more than US$1 million (S$1.25 million).

His practice a few miles away, in a tony section of Tulsa where plastic surgeons operate and locals congregate at bistros and stores such as Saks Fifth Avenue, has a fair-market value of around US$851,000.

Property and tax records show Harrington owns another residence in Carefree, Arizona, in an area of upscale homes tucked into in the boulder-strewn mountains north of Phoenix.

Nobody was at home Saturday at the low-slung, 1950s-style vacation home, across from the Boulders Resort.

Neighbours said they had seen a lot of activity at the home in recent weeks.

Harrington's malpractice lawyer, Mr Jim Secrest II, did not respond to phone messages left Thursday or Friday.

A message at Harrington's Tulsa office said it was closed and an answering service referred callers to the Tulsa Health Department.

Ms Suzy Horton, an old friend of Harrington's, said she can't believe the allegations about the man who removed two of her teeth in the early '90s.

Ms Horton's ex-husband sold Harrington his home in Carefree - a home where she once lived.

"I've been to dentists my whole life, so I know what a professional office looks like," Ms Horton, who now lives in Phoenix, said in a telephone interview. "His was just as professional as anybody."

Ms Horton hasn't seen Harrington in years, but she said he has sent her a Christmas card and wreath every year since her 1999 divorce.

"It was a long time ago, so I suppose anything can change, but the kind of person they're portraying in the news is not the kind of person who sends you a Christmas card", she said.