Up to eight patients could have been treated with equipment that had not been fully sterilised at Tan Tock Seng Hospital's (TTSH) Dental Clinic between Nov 28 and Dec 5.
As it does not know who these patients were, the hospital said that it was contacting all 575 dental patients who were treated during that period to reassure them that their risk of infection was extremely low.
This is because the instruments had undergone two rounds of sterilisation. "At this stage, close to 100 per cent of organisms of concern would have been eradicated," the hospital said. The instruments had, however, missed the final round of steam sterilisation to remove bacterial spores.
As a precautionary measure, all elective procedures at the Dental Clinic had been suspended since last Saturday to allow a safety timeout.
Meanwhile, the hospital and the National Healthcare Group are conducting thorough reviews of procedures and processes, which had already been tightened following a similar case at the National Dental Centre Singapore (NDCS) in June last year.
Health Minister Gan Kim Yong expressed his disappointment that this could happen even after learning points were shared across the healthcare system following the NDCS case. On that occasion, 72 instrument packs were not completely sterilised.
Mr Gan stressed that patient safety was paramount.
He said: "We take a serious view of the incident at TTSH Dental Clinic, and I am disappointed it has happened despite our efforts.
"MOH (Ministry of Health) will study the incident closely, consult relevant technical experts and consider further actions to be taken to reduce the risks of a re-occurrence across the healthcare sector.
"This incident is a timely reminder to all healthcare institutions to maintain a high level of vigilance in delivering patient care safely at all times."
MOH has directed TTSH to conduct thorough reviews of the incident and to report the findings and follow-up action.
Explaining the latest lapse, the hospital said that it puts dental instruments through three stages of sterilisation. First, they are manually washed and further sterilised using an ultrasonic machine. Next, they are air-dried. Finally, the instruments are put through an additional step of steam sterilisation.
Checks last Wednesday revealed that eight packs of instruments which were processed on Nov 28 had not completed the last step of the sterilisation process, but were still used to treat patients at the clinic.
Associate Professor Thomas Lew, chairman of the hospital's medical board, said: "We sincerely apologise to our patients and their families for the lapse and distress caused."
He said additional measures are in place to "bolster and improve our vigilance and workflows" to ensure patient safety.
No patients were infected in the NDCS incident, but four NDCS staff were disciplined and tigh-ter procedures put in place across the public healthcare system.
"This incident shows, however, that further improvements are necessary," said TTSH.
The fear is that non-sterile tools could transmit infectious diseases from the previous patient on whom the equipment was used. Dental treatments usually result in some bleeding, which makes contact with contaminated equipment dangerous.
MOH said it has instructed public healthcare institutions to remind all staff of the importance of checking that instruments used in patient care are properly sterilised before allowing the tools to be used.