Aim This systematic review aimed to assess the effectiveness of fluoride varnish in preschool children for reducing the incidence of caries into dentine.

Data sources Data came from published and grey literature. Databases searched were: CDSR, Medline, EMBASE, Web of Science, SCOPUS, LILACS and BBO. Hand-searching was done of nine dental journals and two medical journals. Backward citation searches were carried out on the reference lists of identified trials and relevant systematic reviews. Trials registers (Current Controlled Trials, ClinicalTrials.gov, EU Clinical Trials Register, Australia New Zealand Clinical Trials Registry, and Registro Brasileiro de Ensaios Clínicos) were searched for ongoing trials. Grey literature was searched via a number of resources including International Association for Dental Research (2001-2018) and European Organisation for Caries Research (1998-2018) conference abstracts and Open Grey, EThOS, the New York Academy of Medicine (GreyLit Report) and Banco de Teses CAPES.

Study selection Inclusion criteria were; the use of fluoride varnish (different regimes and doses were included), randomised controlled trials, preschool age (under 71 months) and over 12 months follow up. Outcomes were caries into dentine and hospitalisations due to caries. A combination of free text and controlled terms were used based on the study question. A total of 2441 studies were identified at initial search, 20 were included for narrative and quantitative analysis after full text reviews of 79 studies.

Data extraction and synthesis Data was extracted independently by two reviewers with a third resolving any disagreement. Data was combined by subgroup to compare different interventions and controls, with a global random effects meta-analysis performed on 16 studies to provide a relative risk (RR) of dentinal caries at the individual level. At the individual level meta-analysis was by RR, at the tooth and surface level this was prevented fraction (PF) and weighted mean difference (WMD).

Results Only one study was determined at low risk of bias, with four unclear and 14 at high risk based on the Cochrane risk of bias tool. Studies were from 13 different countries. Children at baseline were from 0-100% caries free, with a dmft of 0-6.57 and aged 6 months – 5 years. There were no studies reporting hospitalisation due to caries.

The combined RR for the outcome of dentine caries for an individual was 0.88 (95% CI 0.81-0.95) based on 16 studies with considerable heterogeneity (I2 = 75.7%). Tooth level results gave a PF of 31.13% (95% CI 21.08, 41.18) and a WMD of -0.30 (95% CI-0.69, 0.09) for fluoride varnish. At surface level the PF was 24.15% (95% CI 12.91-35.38) and WMD of -0.77 (95%CI; -1.23, -0.31).

Conclusions The conclusions of the paper were that there is modest and uncertain evidence for fluoride varnish reducing the risk of developing dentine caries in pre-school children.