A leading dentist recommends that many preschoolers in fluoridated areas should use low-fluoride toothpaste to avoid the risk of unsightly, mottled teeth.

But Dr Callum Durward, formerly of Auckland University of Technology and the Auckland District Health Board, said this only applied to young children at low risk of dental decay because of factors like good diet and regular brushing.

Dr Durward, who now practises and teaches paediatric dentistry in Cambodia, said those at high risk of decay should use the adult strength for its greater protection. Young children should use just a small smear of paste, on a child-size brush, spit out (not rinse) and must not be allowed to eat toothpaste.

His advice differs from that of the Health Ministry, which recommends using adult-strength fluoride toothpaste at all ages once teeth come through, irrespective of whether the local water supply has fluoride added.

The ministry’s chief adviser on oral health, Dr Robin Whyman, said that families at low risk of dental decay and living in fluoridated areas might choose to use child-strength fluoride toothpaste for children under 6 years.

Dr Durward and colleagues, who studied the teeth of 9-year-old Aucklanders for the latest New Zealand Dental Journal report that “it is widely recognised that fluoride can have both beneficial and harmful effects” on teeth.

Some children in fluoridated areas who swallowed too much fluoride toothpaste would end up with “mottling that doesn’t look good”.