Merthyr Tydfil was a new entrant in the study of children's teeth

The British Association for the Study of Community Dentistry found five-year-olds in the town have an average 3.73 decayed or missing teeth.

Merthyr recorded the most number of decayed, missing or filled teeth among five year olds , ahead of cities including Glasgow and Manchester.

Merthyr dentist Huw Jones said much of the problem was preventable by parents.

"It's when sweets and fizzy drinks become the norm rather than a treat," he added.

To 10 blackspots (number of decayed or missing teeth for average five-year-old) Merthyr - 3.73 North Kirklees - 3.69 Argyll and Clyde - 3.67 Blaenau Gwent - 3.49 Greater Glasgow - 3.45 Preston - 3.3 Bolton - 3.23 Caerphilly - 3.2 Knowsley - 3.14 Bradford - 3.14

Blaenau Gwent came fourth with its five-year-olds having an average 3.49 decayed, missing or filled teeth, while Caerphilly was eighth with a figure of 3.2.

Stuart Geddes, director of the British Dental Association Wales, said: "The figures reflect dental health in that part of the world.

"It is linked to the economy of the area, the difficulty in access to dentistry and part of it has to be down to the unwillingness of the parents of that particular group to seek care for them."

Huw Jones, a member of a dentist practice which still takes NHS patients, said the results were "disappointing but not in the least bit surprising".

The study looked at children's teeth across the UK

"It paints a picture of Merthyr as a whole being bad but there is good and bad out there," he said.

He said he and his colleagues tried to be "diplomatic" in the advice they offered to parents, but that advice was not always followed.

"The children are allowed to have far too many sweets and far too many fizzy drinks, and its frequency of consumption (that is the problem) rather than quantity."

'Some success'

Ted Wilson, chief executive of Merthyr Tydfil local health board, said it was "a very serious issue, but not a new one".

He said they had a "triple track approach" to the problem, as they seek to raise the number of NHS dentists in the area, increase the numbers of people who register and develop their oral education programme.

"We have had some success, but Merthyr still stands out," he said.

In a statement, the Welsh Assembly Government said it was "funding an initiative to help protect the teeth of children who are at risk of developing tooth decay".

The study has been published by toothpaste firm Colgate.