Introduction

Oral health is a global public health challenge with oral diseases estimated to be the most prevalent condition in the world.¹ Untreated dental caries (tooth decay) of the deciduous teeth affects 8% of the global child population, with greatest prevalence in those under 5 years of age.² In Scotland, at the beginning of the 21st century, dental caries in 5 year olds was among the worst in Europe, with 60% affected, wide inequalities identified and no improvement observed in the previous decade.³

A 2002 Scottish Government consultation resulted in fluoridation of the public water supply being ruled out,^{4 5} but with a realisation that a traditional health education approach for oral health improvement was both ineffective and could potentially widen inequalities.⁶ The resultant national oral health strategy established demonstration pilot projects which developed into the national child oral health improvement programme—Childsmile.⁷ The Childsmile programme is described in detail elsewhere⁸—briefly, it is a multicomponent preventive programme operating at upstream (policy), midstream (community) and downstream (clinical) levels. It follows a proportionate universal approach—delivering both universal interventions to all children and additional targeted interventions focused on children predicted to be at higher risk of dental caries from the most socioeconomically deprived backgrounds, with the twin aims of improving child oral health and reducing associated inequalities in the population.^{9 10} Childsmile’s main focus has been on preschool children (aged up to 5 years). The four main interventions of the programme for this age group are (1) dental health support worker (DHSW) home and community contacts (targeted from birth to children and their parents/carers in greatest need as identified by health visitors, for prevention advice, to help facilitate attendance in primary care dental practice, and to link families with community assets); (2) nursery (kindergarten) fluoride varnish applications (FVAs) (targeted to children from the of age 3 years from the more deprived communities, applied twice per year by extended duty dental nurses); (3) primary care dental practice visits (available from birth for all children attending where toothbrushing instruction, diet advice and FVAs are offered); and (4) nursery-supervised toothbrushing (universal to all preschool establishments in Scotland, including daily toothbrushing with fluoride toothpaste and distribution of toothbrush/toothpaste packs for home use). Following piloting, these interventions were collectively rolled out nationally from 2010/2011.

A monitoring and evaluation strategy for the Childsmile programme was developed based on recommended approaches for the evaluation of complex interventions.¹¹ A theory-based approach to evaluation, incorporating a logic model, guided the development of studies to gather process and outcome measures. The evaluation plan included an ecological evaluation of nursery-supervised toothbrushing,^{12 13} an embedded randomised controlled trial of nursery fluoride varnish¹⁴ and an individual child-level data linkage study using the emerging NHS Scotland infrastructure (this present study).¹⁵

Several Cochrane reviews show effectiveness of the fluoride-based interventions^{16 17}; however, the evidence in relation to the proportionate universal delivery of combinations of these interventions at the population level is untested. Here, we developed a cohort using data linkage methods of routine administrative data to assess the reach of the Childsmile programme (with its universal and targeted interventions) by area-based socioeconomic deprivation and to undertake an analysis of the impact of the Childsmile interventions on dental caries outcomes among Primary 1 children (age range 4–6 years old) in 2014/2015 in Scotland (the first cohort of children to be born into the nationally rolled-out programme) by the overall population and then by area-based socioeconomic deprivation…