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A 64-year-old woman has died after a dentist attempted to extract 20 teeth from her mouth.

Dr Rashmi Patel was performing the procedure on Judith Gan on 17 February when she lost consciousness in the state of Connecticut.

Patel's assistant had tried to stop him before calling the emergency services, according to New York Daily News. But it was too late and she had "already flat-lined".

"Gan did not have to die to receive this dental treatment and it is because of Patel's negligence that she died," said a dentist reviewing the case for the state department of public health.

Patel has since had his licence revoked in the US and has been suspended, pending a further hearing next month in front of the state dental commission.

"He has been ordered to stay away from his patients after one died and another spent six days in the hospital," state health officials said.

In a report, the state department of public health wrote: "He wanted to complete the placement of implants as the assistant begged Patel to stop working, and finally ran out and called 911, but the patient had already flat-lined.

"The four count petition found, among an array of other misdeeds, that Patel deviated from standard of care in that he did not timely and properly respond to Gan's oxygen desaturation and/or respiratory distress and/or cardio-pulmonary distress."

Patel was also sued for malpractice by a former employee in 2009 after he performed "shoddy" dental work on Doreen Jasonis. She won nearly $500,000 from a jury in 2011, but the ruling was appealed and ended with an out-of-court settlement.

Patel will fight the charges against him meanwhile his clinics in Enfield and Torrington remain open.