As many as 7,000 people may have been exposed to HIV and hepatitis viruses at an oral surgery dental clinic Tulsa, OK, health officials said today.

By noon today, more than 400 people had called a hotline established to answer questions about the dental clinic under investigation, while all patients would be notified by letter.

The investigation by public health authorities there began after one of Dr. W. Scott Harrington's patients tested positive for HIV and hepatitis C, though a subsequent blood test showed negative results for HIV.

Tulsa Health Department officials told CNN they were left "grasping for words" after seeing the doctor's dental practice, with dental assistants performing procedures for which they were under-qualified. Employees also mishandled needles and sterilization procedures.

"I will tell you that when... we left, we were just physically kind of sick," said Susan Rogers, executive director of the Oklahoma Board of Dentistry. "I mean, that's how bad (it was), and I've seen a lot of bad stuff over the years."

Officials said the dentist allowed unauthorized employees to perform intravenous sedation of patients, as well.

Tulsa Health Department officials said the doctor's patients are being offered a free blood screening - no appointment necessary - at the North Regional and Wellness Center in Tulsa. The Oklahoma Dental Board cited Harington for a number of safety and health violations that put his patients at risk. He is scheduled to appear before a dental board hearing later this month and has voluntarily closed his practice and remitted his medical license.

The American Dental Association said individual states are charged with regulation of dental practices, including licensing, inspection and the overseeing of drugs. Dr. Matt Messina, a spokesman for the organization, said: "This is exceedingly rare. ... I'm just angry, because this is a case I think is so far outside of the bounds of normal that it makes it remarkable."