More than 2.4bn people have untreated tooth decay across the globe, a study in the Journal of Dental Research suggests.

Experts say it is alarming it has been neglected to this level - despite known ways to both treat and prevent it.

They warn that dental decay can lead to severe pain, infections, days off work and problems with childhood growth.

And the analysis shows it is not just a childhood problem. Scientists say it should be seen as an adult disease too.

'Consuming budgets'

Tooth decay occurs when acids in the mouth dissolve the outer layers of teeth. It is also known as dental decay or dental caries.

If not treated it can lead to problems such as a cavities, gum disease or abscesses.

Prof Wagner Marcenes of Queen Mary University of London led an international team of scientists analysing 378 studies involving some 4.7m people between 1990 and 2010.

Their global survey suggests 2.4bn people have untreated tooth decay in their permanent teeth and some 621m children have untreated decay in milk teeth.

According to UK data, a third of the population had untreated dental decay in 2010. In Lithuania, one of the hardest-hit countries, the proportion was more than double this, at 68%.

Their work predicts more than 190m new cases of dental decay every year.

Prof Wagner says the main reason behind this is diet - eating and drinking high amounts of sugary foods and drinks and frequent snacking.

He said: "It is alarming to see prevention and treatment of tooth decay has been neglected at this level.

"Tooth decay is a significant economic burden. And if left untreated, it leads to poor productivity at work and absenteeism in adults, and poor school attendance and performance in children."

But the review suggests a shift in the burden of caries from children to adults.

Prof Marcenes said: "The current perception that low levels of decay in childhood will continue throughout life, seems incorrect.

"Yet most policies are focused on children - adults are neglected."

He suggests health messages should be considered in adult workplaces too.

Professor David Williams, an expert in global oral health at Queen Mary University of London, who was not involved in the research, added: "What is clear is that this is a major public health problem.

"And there is a major tension here - this is a disease that is prevalent and yet preventable and is consuming budgets.

"But the likelihood that the oral health community will be able to fight this battle single-handedly can be challenged."

The international team included researchers from the University of Washington, Seattle, and the University of Queensland, Australia.

Source: BBC