More than 600 patients who were treated by a bogus dentist are being warned they may have been put at risk of contracting HIV and hepatitis.
Omid Amidi-Mazaheri and his girlfriend were jailed in March
Omid Amidi-Mazaheri was jailed for two years in March for treating patients at practices in Norbury, Tulse Hill and East Dulwich, south-east London.
Health authorities say the 41-year-old, from East Dulwich, may not have followed infection control procedures.
Letters have been sent out to arrange blood tests for the patients involved.
Angela Dawe, of Lambeth Primary Care Trust (PCT), stressed the risk of being infected during dental treatment was "small" but added "we can only rule it out by testing a blood sample".
Letters have been sent to 599 people and the PCT said they were hoping to trace "a handful more".
Ms Dawe said that sessions would be run over the next few weeks offering both dental and blood checks.
"We deplore Amidi-Mazaheri's dishonesty and the way he abused the trust of his patients and the NHS.
"He was not employed by the local PCTs and we only became aware of the seriousness of the case as the criminal investigation progressed," she said.
Amidi-Mazaheri carried out often painful treatment, between September 2002 and February 2004, and used the profits to fund a luxury lifestyle.
He drilled out cavities without a local anaesthetic then installed expensive fillings that crumbled within days.
On one of the rare occasions when he did give an injection, he dropped a piece of equipment down the patient's throat.
His girlfriend, qualified dentist Mogjan Azari, was also jailed for a year. Between them they are believed to have pocketed more than £120,000.