Roughly 600 veterans are at risk of possible HIV and hepatitis infections after being treated at a Veterans Affairs medical center in Wisconsin.

A dentist at the VA medical center in Tomah, Wisconsin, was caught re-using his own dental equipment instead of using the disposable, sterilized equipment as the VA requires. Officials were alerted after a fill-in dental assistant noticed the dentist cleaning his own equipment to re-use on his patients and reported the breach in protocol.

Officials said the dentist used the improperly sterilized equipment on his patients for an entire year, from October 2015 to October 2016. He saw 592 patients within that timeframe.

Tomah VA medical director Victoria Brahm told reporters in a press conference earlier this week that the dentist willfully violated protocol and that they had referred the case to the inspector general for a review of possible charges.

"During all of the orientation, he used our equipment. He used it appropriately, so it was very purposeful from what we found in our investigation that he knew exactly what he was doing, and preferred to use his own equipment against procedure," Brahm said.

After reviewing medical records and risk of disease transmission, the patients have all been notified and the VA has offered a free screening to all those who could have been exposed to HIV, hepatitis B, and hepatitis C. They have also offered free treatment for anyone who tests positive.

The dentist, who was not identified, was initially removed from his role and transitioned to an administrative position while he waited to appear in front of the review board on Monday, but the Milwaukee Journal Sentinel reported late Friday that the dentist has now resigned. Before the resignation, United States House Speaker Paul Ryan publicly questioned why the dentist had not been fired from the medical center.

"This news is not just heartbreaking; it's outrageous," Ryan said in a statement. "How can our veterans be treated so carelessly and where is the accountability?"

"The individual in question has not even been fired -- a truly stunning show of bureaucratic impunity," he added. "This demonstrates once and for all that the VA needs a complete overhaul, so that our veterans finally get the care -- and the respect -- they deserve."