And dental conditions are the leading cause of preventable hospitalisations for children and teenagers, ahead of asthma and ear, nose and throat infections.

While you might expect to find most emergency rooms busy with broken bones and disease, experts say a surprisingly large number of people are turning up with painful swollen mouths, a telltale sign of decay.

Professor David Manton, a paediatric dental expert with the University of Melbourne, said  at one emergency department half of the children patients presented because of dental decay.

"It's horrifying that in a society such as ours, this still occurs," he said.

He said it could be demoralising to be called into an emergency department late at night, where he sees children with "fat faces" because of dental abscesses.

Every year close to 70,000 Australians are admitted to hospital with dental conditions considered preventable with better hygiene, diet or earlier treatment, according to Australian Institute of Health and Welfare data analysed by finder.com.au.

This includes about 6700 Victorian children and teenagers.

Some have such bad decay that all the child's teeth have to be removed.

Professor Manton said their teeth could look like "little apple cores, with holes in between”.

"Or they can be just black stumps where there is basically no structure left. They are just tops of the roots, because everything has just decayed or broken away."

Clinical Associate Professor Matthew Hopcraft, chief executive of the Victorian branch of the Australian Dental Association, said dentists saw toddlers who already needed all of their teeth baby extracted.

These children were often starting school, and getting their first school photos, with no teeth.

Dr Deborah Cole, chief executive of Dental Health Services Victoria, said it was sad to see a two-year-old child have all their teeth removed.

"Most people are used to seeing kids missing a tooth but when you have no front teeth it's pretty obvious," she said.

"Kids can often be picked on.

"They usually learn to eat properly, but their diet isn't ideal because they go for softer foods that may have caused the problem in the first place."

Dr Cole said in the last 20 years the rates of dental decay in children had significantly reduced.

"[But] there's still a group of people that we haven't reached. They are the people we need to get to."

Dentists said they were still seeing damage in very young children after they were given bottles filled with sugary drinks.

Oakleigh dentist Andrew Gikas​ said he often noticed this extreme decay in children left sleeping with a bottle.

"You don't want children sleeping with milk on their teeth all night. These children will end up having tooth decay," he said.

"Sometimes people are also putting fruit drinks in bottles or dipping dummies into sweet things or honey."

Dentists said adults were also landing in hospital with cavities and abscesses that they had left too long without treatment, either because they feared going to the dentist or because they were worried about the cost.

Cost is still a significant impediment to many people, said Dr Cole.

"One of the things we're finding is that people will often take their children [to the dentist] but not themselves."

According to a 2016 survey, almost 50 per cent of Australians delayed dental treatment in the space of a year because of the cost. And of those who earned less than $50,000 a year, just 9 per cent had seen the dentist in the last year or two.

Free general dental care is only available for a section of the population in Victoria, such as children whose parents are government concession card holders, homeless people and refugees.

Others are eligible for public dental services but have to pay a subsidised fee of about $30, or up to $338 for specialist services.

The story, 'Horrifying this still occurs': Extreme tooth decay lands thousands in hospital, first appeared on The Age.