More than 3,000 dental patients are being contacted over concerns a Cardiff dentist re-used equipment that should have been binned.
Mark Roberts was dismissed after a whistleblower claimed he re-used syringe cartridges and root canal surgery files.
He had worked at Splott Road Dental Surgery from 1989 to February 2015.
The dentist said he deeply regretted "lapses" at his practice, as health bosses contact all former patients.
Cardiff and the Vales University Health Board and Public Health Wales have also set up special advice lines for anyone who is concerned about the possibility of being infected by another patient.
However, patients are being assured that there is a very low risk of transfer of infections like hepatitis B, hepatitis C and HIV.
Blood tests will be arranged for those deemed to be at a higher risk of infection or to give peace of mind to those who are worried.
In a statement, Dr Roberts said: "I deeply regret there have been occasional lapses in my practice, and I have sought to address these.
"I have only ever wanted to provide the very best care for my patients."
The claims of poor infection control include:
- That Mark Roberts re-used the cartridges of local anaesthetic syringes. These should have been thrown away after a single use. It is understood he did not re-use the actual needle.
- That he also re-used endodontic files which are used for root canal surgery. These should have been disposed of after being used by each patient.
The General Dental Council confirmed that Mr Roberts was suspended for 18 months in April, and this has been "continued" until October 2016 due to "concerns about his cross-infection controls".
Ruth Walker, executive nurse director at Cardiff and Vale University Health Board, said they had sent letters to 3, 245 patients who were registered with Mr Roberts at the time the concerns were raised in February.
But she said they are aware there could be many more people affected who were previously his patient.
She also reassured people that the surgery is now under new ownership.
"We would like to reiterate that these issues are historical and there is no reason for patients currently registered at the dental practice to be concerned about the care and treatment they receive," she added.
She said the health board was alerted to the concerns by the new owners of the dental practice, Integrated Dental Holdings (IDH) in February.
IDH had bought the surgery from Mr Roberts in November 2014, during which they checked procedures and spoke to staff.
A member of staff then raised concerns about the NHS dentist.
The problems had not been picked up during previous inspections of the surgery.
Mr Roberts was suspended and dismissed by IDH, who are now working with the health board to investigate what happened.
Dr Meirion Evans, consultant epidemiologist for Public Health Wales, said: "Based on clinical advice, we would not recommend screening for all patients as the risk is very low unless you have other lifestyle factors which may present a greater risk of transmission.
"However if patients still have concerns after contacting the advice line, a simple blood test can be arranged to offer them peace of mind."
The advice line is 0800 952 0055
It will be open from Tuesday 20 October at the following times:
Tuesday, 20 October 2015: 12:00-22:00 BST
Wednesday, 21 October to Friday, 23 October: 08:00 to 20:00 BST
Saturday, 24 October to Sunday, 25 October: Closed
Monday, 26 October to Friday, 30 October: 09:00 to 17:00 GMT