Serious tooth decay in children as young as two is being either ignored or badly treated as a result of a system of "poor care" and "supervised neglect", a leading dental expert has warned.

Young children are suffering pain, facial infections and blood poisoning because their baby teeth are being left untreated, with some undergoing the trauma of having teeth extracted because many dentists wrongly think primary or "milk" teeth are not worth repairing, said Monty Duggal, a professor of children's dentistry.

The mistaken belief that baby teeth should not be filled is leading to NHSdental hospitals having to perform emergency removals of children's teeth – which can sometimes involve extracting every tooth in what is called a "full clearance" – he adds.

Writing in the Faculty Dental Journal, Duggal criticises dentists and parents who believe that problematic milk teeth can be left to drop out naturally.

He condemns non-intervention in such children as "wrong and unjustifiable", and asks: "How can we condone the non-treatment of a disease that carries such a high morbidity and knowingly put the child at risk of pain and suffering?"

Duggal, the head of paediatric dentistry at the NHS's Leeds Dental Institute, writes: "We must ensure that those children who still get caries [dental decay] do not suffer further from the provision of poor care and its consequences.

"Specialists in hospitals treat children on a daily basis with severe oro-facial infections caused by poor restorations, placed with a disregard for good restorative principles or a non-interventionist 'keep under observation' approach.

"Hospital paediatric dental services across the UK are replete with children referred by general dental practitioners for pain due to untreated or inadequately treated caries in the primary dentition," said Duggal.

That workload shows that the current neglect of children's teeth "has serious cost implications" for the NHS, he adds.

Most of the children suffering in this way are from the country's poorest families, Duggal stresses.

Those from deprived backgrounds are worst affected because of poor diet, lack of dental education and never being taken to see a dentist by their parents. As a result, about 80% of all dental disease in children occurs among those in social classes IV and V.

Children in poorer areas can have eight times as many dental problems as those in better-off families, research shows.

Duggal disputes the belief among dentists that treating decay in children's first teeth would unsettle them, adding: "I have been unable to find any convincing evidence in the literature that leaving primary teeth untreated in children is not likely to cause at least discomfort and in many cases pain and suffering.

"Sometimes dentists don't think it's important to fill baby teeth to a high standard because they will fall out by the age of 12 at the latest."

As few as 10-12% of decayed primary teeth are repaired, and it can be as few as 5% in some areas, which is "a matter of national shame", says the article in the journal, which is produced by the Royal College of Surgeons of England.

Duggal sees 10-15 children a week, aged between three and eight, with severe toothache from several decayed teeth. Most are from the most deprived estates in Leeds.

He blames the NHS's way of funding dentists for producing "supervised neglect" of children's teeth. Dentists serving poorer communities find that the money they need to undertake sometimes extensive work is unavailable because payment, by Units of Dental Activity (UDAs), is capped. The system "fails to recognise the increased treatment needs of such children" and "includes economic disincentives to the provision of such intervention", Duggal writes.

The British Dental Association, which represents the UK's 23,000 dentists, said that there was "a clear and unacceptable chasm between those with the best and worst oral health. The gap is depressingly correlated with social deprivation."