When Mr Tim Leo took his 13-year-old son Ethan to the nearby WH Dental Surgeons in Hougang to fix his crooked teeth, as it offered orthodontic services, he expected a routine treatment lasting one to two years.

But he grew concerned after a year when there were no visible changes to Ethan's teeth, even though the dentist had already extracted eight to make space in the boy's "overcrowded" mouth.

The clinic would give the boy "lots of painkillers" after each session as the braces hurt and caused ulcers in his mouth, he claimed. The studs on the braces would also fall out.

Although his mother had accompanied Ethan for his dental visits, she was not allowed into the room when the procedure was conducted.

When she asked Ethan about the treatment, he told her that the braces were fixed by two young men and the dentist, Dr Sng Wee Hock, would pop in to have a look.

When Mr Leo, a project manager with an American firm, quizzed the clinic about this, he was told that all treatments were done by Dr Sng and no one else.

On the advice of friends, he took Ethan to another dentist, an orthodontist who specialises in braces, for a second opinion.

That was when he hit the roof.

The orthodontist told him that there had been no need for the boy to have his four wisdom teeth extracted. She was surprised at their removal as she said dentists try to preserve teeth where possible.

She also said the wiring for the braces was wrong, which was why Ethan had ulcers in his mouth.

Mr Leo said: "I trusted Dr Sng when he said there was overcrowding and that the wisdom teeth had to be pulled out."

The cost of pulling out the wisdom teeth was $4,150. This was charged to Medisave. Pulling out the four premolar teeth came to less than $400.

In March this year, Mr Leo filed an official complaint with the Singapore Dental Council against Dr Sng for unnecessarily pulling out four wisdom teeth and for getting possibly untrained people to fix Ethan's braces.

The trigger, he said, was when he read a report about Dr Sng being suspended by the Singapore Dental Council earlier this year for letting unqualified clinic assistants do the orthodontic work.

Dr Sng has had three other run-ins with the authorities since 2014, such as for making claims against Medisave for costly procedures he did not do. He was suspended and fined for the various offences, including two 15-month suspensions that he started serving this year.

Mr Leo said he received a letter earlier this month from a lawyer representing Dr Sng, offering a financial settlement. He refused, saying that he made the complaint because he does not want other children to go through the same experience his son did.

Dr Sng, through his lawyer, has declined comment.

Dr Seah Tian Ee, president of the Association of Oral and Maxillofacial Surgeons, told The Sunday Times: "At 13 years old, the wisdom teeth are still at an early development phase and the facial skeleton has not reached maturity."

He said: "It is not routine practice to remove wisdom teeth at 13 years old unless they are associated with pathology such as cysts or tumours."

Dr Seah also said that the upper wisdom teeth in such a young boy are usually "closer to the maxillary sinuses" making them more technically difficult to remove with a high risk of perforation.

But he added that there might be some orthodontic reasons for removing wisdom teeth in children.

Dr Ivan Lim, a senior orthodontist at the National Dental Centre, Singapore, said removing the four premolars was justified to create the space needed, but the wisdom teeth removal was not necessary for brace treatment.