Mary Ann Robinson visited Dr Hock Nien Ng with a toothache in December 2009.

An inspection revealed the upper right molar had extensive decay under an existing filling.

Dr Ng told her the options were either a tooth extraction or root canal therapy.

She opted to have the tooth pulled, but the procedure went wrong when the crown of the tooth broke.

Dr Ng continued with the extraction, taking breaks in between to see other patients, and managed to remove part of the root of the tooth.

He then took a further X-ray and continued, but accidently pushed the remaining part of the tooth into her sinus cavity.

Dr Ng stitched the socket and told her she required surgery.

Ms Robinson then went to Calvary Hospital's emergency department after feeling ill and was referred to the maxillofacial unit at Canberra Hospital.

She was given antibiotics in preparation for surgery.

She reported that water would come out of her nose when she had a drink.

But Ms Robinson lost control and sensation in the right side of her face – which was later diagnosed as Bell's Palsy – and developed an infection which required admission to hospital.

She underwent surgery about a week after the botched extraction, with doctors successfully removing the piece of tooth that had been freely moving within her sinus cavity.

The operation was successful, but Ms Robinson then lost sensation in her upper teeth and gums.

She then suffered an infection to her jaw bone and required treatment until September 2011.

Ms Robinson's career as a vet was severely affected by her continued health issues.

She launched civil action against the dentist, claiming personal injury as a result of negligence.

But Dr Ng argued he had continued the procedure upon her instruction.

Master David Mossop, in a judgment published in the ACT Supreme Court on Tuesday, found in Ms Robinson's favour and awarded her $808,114 to cover damages, loss of income, and out-of-pocket expenses.

Master Mossop found Dr Ng had breached his duty of care by failing to refer her to a surgeon and continuing his attempts to extract the tooth after the second X-ray.

"[Dr Ng] continued the extraction in circumstances where a reasonably competent general dentist would have recognised that the risks associated with continuing were significantly greater than if the plaintiff was referred to an oral surgeon," Master Mossop wrote.

"Notwithstanding the expressed wishes of the patient, it is the dentist that remains in control of the procedure and whether or not it is pursued.

"The desire of the patient to have the process successfully completed does not compel or justify a dentist in continuing to persevere when the risks outweigh the benefits."

Master Mossop said he had been satisfied that the dentist had breached his duty of care to Ms Robinson and that the breach caused the wall of the maxillary sinus to be perforated.

"Had the plaintiff, no later than the second X-ray, been referred to an oral surgeon then it is likely that the roots of the tooth would have been able to be extracted without a communication with the sinus being created.

"Even if I had accepted [Dr Ng's] version of events, I would have found him to have breached his duty."