Some 66 patients, most of them children, are being recalled for blood tests by the Health Service Executive (HSE) after a dentist who treated them tested positive for HIV.
The patients' families, all in the Dublin region, received notification of the recall this week but this only came to light yesterday.
The HSE said the dentist worked in two locations in the region, but would not identify them.
The dentist was diagnosed with HIV last October after feeling unwell. The HSE said it immediately made sure the dentist had no further contact with patients.
Asked why it was only now contacting patients treated by the dentist, some nine months later, the HSE's director of public health, Dr Brian O'Herlihy, said it took some time to identify the patients who should be contacted. Only patients who would have had open wounds in their mouths as a result of treatment by the dentist were being recalled for blood tests.
Dr O'Herlihy said there were national guidelines in place on how to deal with situations which arose when a healthcare worker was diagnosed with a blood-borne infection.
In accordance with these an expert group was formed to advise on what steps should be taken, and following its deliberations the families of 66 patients were contacted by telephone or letter on Tuesday of this week.
So far 31 of these had had blood tests and all were negative for HIV.
Another nine will be tested on Monday, and Dr O'Herlihy said some families had put off tests for the moment because of holidays. Some others had said they did not want a test to be done in their children's cases.
The majority of the 66 patients are aged eight years, and most of the remainder range in age from six to 18. However, a small number of older adults are also included.
Many of them would have been referred to the dentist as a result of school checkups.
Children in schools have dental check-ups when in second, fourth and sixth class.
Dr O'Herlihy confirmed the dentist was recruited by the HSE to work in the public dental service in September 2005.
He said dentists were not screened for infections such as HIV at the time of their recruitment. This was not currently required by national guidelines.
He would not say if the dentist was recruited from abroad, but said the HSE was satisfied the dentist had not worked in any private dental practice in the Republic before taking up the position with the HSE almost two years ago.
The HSE confirmed some families were shocked, upset, dismayed and angry when they received notification of the matter this week, while others were not bothered.
The HSE said counselling would be provided if required, but it claimed anxiety to patients was minimised by the fact that they were offered blood tests immediately and arrangements were in place to have the results back to them within 24 hours.
Dr O'Herlihy said the expert group might have been more hasty in their deliberations had they not been aware that the possibility of transmission of HIV to the patients was "extremely remote".
He stressed that since HIV was first identified 25 years ago there has been only one documented case worldwide of a HIV-positive dentist infecting patients.
This occurred in the US around 1989/1990, and resulted in strict infection control regulations being put in place for dentistry across the globe.
"The local expert group were well aware of the situation and they would have dealt with it, I think in a quicker manner ... had they felt that there was any significant risk of transmission," he said.
"This is purely a precautionary exercise.
"It doesn't alarm us in any way because we don't expect that there's the slightest, remotest chance of infection having been transmitted in this case...We are taking an ultra-cautious position in making contact with these 66 patients," Dr O'Herlihy said.
He went on to apologise to the patients for any inconvenience or anxiety caused.
He said it was the first time such a case had come to light in dentistry in the Republic.
He would not identify the dentist, and said "this really is quite a tragic situation for the healthcare worker concerned because it affects a career perhaps".