Straightening children's crooked teeth with braces may improve their smile but it is no guarantee of happiness and improved self esteem.

A 20-year study by scientists in Britain that looked at the impact of braces on more than 300 children in Wales showed that having straighter teeth had little positive impact on their psychological health later in life.

When they were questioned as adults, none of them regretted having had their teeth improved and most were satisfied with the way they looked. But there was no difference in their psychological wellbeing when compared to other people who have never had braces.

"On the basis of our research if there are irregularities, and especially if they are not severe, then there will be no harm to dental health and it wouldn't change their life happiness in the future if they don't wear braces," said Professor William Shaw, an orthodontist at the University of Manchester in England.

Each year countless children around the globe receive orthodontic treatment to align their teeth or correct other irregularities.

Parents can spend a small fortune on their children's dental work. In Britain, braces can cost 2,000 pounds ($3,915) or more depending on the severity of the problem.

All the people questioned in the study published in the British Journal of Health Psychology had quite significant dental irregularities and had received braces free through Britain's state-funded National Health Service (NHS).

"It can be concluded that, although in general participants' self-esteem increased over the 20-year period, it was not as a result of receiving braces," Shaw said.