Children from smoky homes visited the dentist more often

They believe it is possible that one of the ingredients of passive smoke may make children less able to fight off the bacteria that cause tooth decay.

That gives us one more piece of information that passive smoking is bad for children Andrew Aligne, researcher

The research, published on National No-Smoking Day in the Journal of the American Medical Association, was carried out by a team from the University of Rochester in New York State, US.

They studied 3,500 children aged between four and 11 - and concluded that one quarter of them would not have developed cavities in their first set of teeth if passive smoke had not been present.

Blood chemical

The children had higher levels of nicotine derivative cotinine in their blood, which scientists believe it may suppress the immune system.

Dr Andrew Aligne, who led the research, said: "That gives us one more piece of information that passive smoking is bad for children and that all children deserve to grow up in a tobacco free environment."

The study is not proof that passive smoke contributes to cavities, as it is known that social class has both a strong influence on whether adults smoke - and also on the family diet.

So it is possible that the cavities which appear to be the fault of smoke are instead the fault of a poor diet.

Meanwhile, the British Dental Association (BDA) called for selective fluoridation of water in areas with the worst incidence of child tooth decay - principally the UK's most populous cities and towns.

In its evidence to the House of Commons All Party Parliamentary Group on Primary Care, which is conducting an inquiry into fluoridation it said that this could be the best way to reduce inequalities in dental health.

In Birmingham, where water has been fluoridated for four decades, children's teeth are "three times healthier" than those of children living in Manchester, which is not fluoridated.

While there are some public concerns about the health effects of fluoridation, no evidence of adverse effects has been discovered.