Up to 12,000 people have been urged to undergo testing for HIV and hepatitis after health officials confirmed four Sydney dental clinics are under investigation for poor hygiene practices.

It has been revealed that two senior dentists have been suspended and a further 12 are under investigation over a number of breaches involving poor cleaning and sterilisation techniques over a number of years.

New South Wales Health confirmed the four practices are located in the city, Surry Hills, Bondi Junction and Campsie in Sydney's south-west.

Two of them are the Gentle Dentist at Campsie and Sussex Street in the Sydney CBD, which were run by Samson Chan, and the other two were practices at Surry Hills and Bondi Junction run by Dr Robert Starkenburg.

Both Dr Chan and Dr Starkenburg have been suspended from practising.

More than 40,000 patients attended the two Gentle Dentist practices over the past 10 years and officials said more than 11,000 people had invasive surgery which put them at risk of HIV and hepatitis.

About 800 people from Dr Starkenburg's practices are also believed to be at risk.

Suspended dentist says patients not at risk of infection

Dr Starkenburg, who has been a dentist and orthodontist for more than 40 years, said although he was a "hippie", he wanted to practise again despite the controversy.

The 75-year-old denied putting any patients at risk.

"I'm a hippie," Dr Starkenburg said.

Samson Chan (left) and Robert Starkenburg have both been suspended from dental practice because of concerns about hygiene at their clinics. ( Supplied )

"[But] I haven't put them [patients] at risk. I'm sorry if it's been published that I have - but I haven't."

He said an argument with a former patient in November last year led to the complaint made to health authorities.

"Oh yeah he wanted to put me out of business," he said.

Dr Starkenburg said he had changed his practices and was now up to date with the latest sterilisation procedures and would like to be able to return to work as a dentist.

"Public health investigations began that included audits of infection-controlled protocols and procedures within these clinics," Dr Shane Fryer of the Dental Council of NSW said.

"These audits showed that there were some problems with the cleaning, sterilisation and storage of instruments in that it was not being done in compliance with the guidelines of the dental board of Australia.

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"The dental council has interim immediate action, powers to suspend and impose conditions on dental practitioners, and registration, if we believe it is appropriate to do so to protect the health and safety of the public.

"We have taken such action in relation to 12 dental practitioners involved in these serious infection control breaches.

"In March, the dental council suspended the registration of Dr Samson Chan, the owner and principal dentist of the Gentle Dentist at Campsie and Sussex Street Sydney.

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Public information hotline: 1800 610 344 NSW Public Health Unit: 1300 066 055

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"We also suspended four other dentists at Dr Chan's practices and imposed conditions on six other dentists.

"In December, the dental council also took urgent action to suspend sole practitioner Dr Robert Starkenburg who practiced at Bondi Junction and Surry Hills.

"I want to assure the public that there are stringent guidelines in place in relation to infection control, that dental practitioners must adhere to."

Health officials urge some patients to take blood test

Dr Fryer confirmed Dr Starkenburg's practice registration was suspended in December, while Dr Chan was suspended in March.

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Health experts said the risk of infection was low but urged any patients who had surgery or an "invasive procedure" at one of these practices over the past decade to get a blood test.

NSW Health director of health protection Dr Jeremy McAnulty said: "It's believed there is a low risk of transmission of infectious diseases in these circumstances.

"[We're] recommending that some of the patients who had invasive procedures at the Gentle Dentist, and that's around 11,000 patients, and all the patients who had procedures with Dr Starkenburg, see their GP for testing for HIV, hepatitis B and hepatitis C as a precaution.

"It's important to stress we have no evidence of infection at this point, that anybody — any transmission has occurred.

"But the experts have been concerned in light of the reports of the problems with infection control at these facilities, that a risk is there."