The study will compare the effectiveness of Duraphat® fluoride varnish in preventing any further dental decay among 3-4 year old children in nursery schools.

It is important to ascertain the additional preventive value that fluoride varnish may provide when applied in conjunction with other preventive measures which form part of a national dental health improvement programme targeting children at risk from dental decay. 1600 children will be recruited into the study for 2 years.

The objective of this study is to compare the effectiveness of Duraphat® fluoride varnish plus treatment as usual (TAU) with TAU only in preventing any further dental decay.

Thus the study is a clinical trial of treatment as usual (TAU) versus TAU plus fluoride varnish in the nursery school setting. TAU is the core Childsmile Nursery intervention (supervised daily toothbrushing with fluoride toothpaste, free dental packs of fluoride toothpaste, toothbrushes and advice).

Children will be screened by asking parents whether or not the child has previously been hospitalised with asthma or diagnosed with any allergies. Provided that a child has no contraindications to fluoride varnish then the child can proceed to study inclusion. On the day of the planned application, the dental nurse will carry out a risk assessment to reduce the possibility of children with oral/facial infections being included. After excluding non-eligible children, a baseline dental examination will take place, followed by randomisation into treatment as usual or treatment as usual plus fluoride varnish. This second group will receive up to four fluoride varnish applications at 6 month intervals. After two years, all study children will be offered a final dental examination.

Inclusion Criteria:

• Children attending nurseries which cover significant numbers of children whose home postcode is within the most deprived quintile of postcodes as measured by the Scottish Index of Multiple Deprivation (SIMD) (Scottish Government 2011).
• Children in the first year of nursery school (known as the 'ante pre school year'). On average the children will be three years old.
• Every eligible child in participating nurseries will be invited to join the study, irrespective of the SIMD ranking of their own postcode.
• Children with or without pre-existing cavities, as the cavity can be treated through the usual primary care dental service (i.e. as part of 'treatment as usual').

Exclusion Criteria:

• Children with contraindications for the Duraphat® varnish i.e. hypersensitivity to colophony and/or any other constituents, ulcerative gingivitis, stomatitis, bronchial asthma, history of allergic episodes requiring hospital admission (e.g. asthma).
• Receipt of fluoride supplements due to a small risk of fluorosis.
• Abnormalities of the skin around the mouth, lips (e.g. cold sores) and soft tissue lesions.