(CNN) -- More than 500 veterans in Ohio are being contacted by a clinic where they may have been exposed to hepatitis and HIV during routine dental work, according to Ohio Veterans Affairs communications officer Todd Sledge.
The Dayton, Ohio, VA clinic is contacting 535 veterans who received treatment during an 18-year period from a dentist who admitted to not washing his hands or changing gloves between patients. There are 100 to 130 additional patient records still to review, according to Sledge.
"We're taking a very aggressive approach and a well-planned intervention to make sure that we're contacting these folks," Sledge said.
By Tuesday evening, 436 of the 535 patients had been contacted by phone, letters and visits to shelters, according to Sledge.
Individuals sought by the center are known to have been treated directly by the clinician between January 1, 1992, and July 28, 2010, according to a release by the medical center.
The center is offering free tests to those involved and the clinic will provide all necessary care and treatment without charge should a veteran test positive for the viruses, Sledge said.
"The encouragement to get tested is strictly a precautionary measure," Sledge said. "It's a very low risk that there's any potential contamination."
While Sledge said the testing stemmed from "invasive procedures ... done by one single clinician," He did not identify that clinician and he did not release specifics about the clinician's health.
Sledge said the clinic is taking full accountability for those involved, whom he calls, "our nation's heroes."
Last year the clinic closed for a month for "re-education on infection control standards" for the staff, Sledge said. Veterans could still receive care at other facilities, Sledge said.
The dentist, who is currently still on staff but handling non-clinical duties, self-reported himself during an internal inspection.
An investigation is now underway involving reports that other workers at the clinic brought the dentist's hygiene to the attention of the center, concerns that Sledge said were valid.
The center is taking an "ongoing in-depth look at a lot of aspects surrounding the allegations," Sledge said.
"When someone brings those things to your attention," Sledge said, "you need to review what practices are happening."
More information and a list of labs in contractual agreement with the Dayton center is available by calling the VA's hotline at 1-877-424-8214.