Data sourcesPubMed Central, CINAHL, Embase and reference lists of identified articles.Study selectionObservational and experimental studies published in English where breastfeeding was the exposure and development of caries was the outcome of interest were considered. Two reviewers independently selected studies for inclusionData extraction and synthesisStudy quality was assessed independently by two researchers using the Newcastle Ottawa Scale (NOS). Key data items, exposure and outcome definitions and effect estimates (odds ratios (OR), relative risks, prevalence ratios) with 95% Confidence Interval (95%CI) were abstracted where available for inclusion in a meta-analysis. The aim was to assess breastfeeding in two specific time windows; up to 12 months of age and beyond 12 months of age.ResultsSixty-three papers were included. These consisted of 14 cohort studies of which six were nested within RCTs of breastfeeding promotion interventions, three case-control studies and 46 cross-sectional studies. The studies were predominantly conducted in high and middle income countries with only eight studies from low income countries. Forty-six studies were not included in the meta-analysis because of methodological differences in the measures of exposure and outcomes, or reporting of correlational analyses only.Meta-analysis of one prospective cohort and four cross-sectional studies reported odds ratios for the association between children who were exposed to more versus less breastfeeding up to 12 months OR= 0.50; (95%CI; 0.25-0.99, I(2) 86.8%).In the two studies which compared ever breastfeeding in the first 12 months with never breastfeeding, both showed a marked protective effect of breastfeeding on dental caries compared with other feeding. Whereas the three studies which compared a longer duration of breastfeeding in the first 12 months to a comparison group which included children who had had some exposure to breastfeeding did not (34,52,59). A meta-analysis of this three study subgroup found OR= 0.92; (95%CI; 0.69-1.23, I(2) 0%)Meta-analysis of two cohort studies, one case-control study and four cross-sectional studies reported odds ratios for the association between more or less breastfeeding after the age of 12 months and dental caries.Comparison groups for these studies included both those who had never been breastfed and those who had been breastfed for shorter durations. The pooled estimate was OR= 1.99; (95% CI: 1.35-2.95, I(2) 69.3%).Meta-analysis of one cohort, one case-control and three cross-sectional studies reported odds ratios for the association between more versus less nocturnal breastfeeding and the risk of dental caries amongst the subgroup of children breastfed longer than 12 months. OR= 7.14; (95%CI; 3.14-16.23, I(2) 77.1%).ConclusionsBreastfeeding up to 12 months of age is not associated with an increased risk of dental caries and in fact may offer some protection compared with formula. However, children breastfed beyond 12 months, a time during which all deciduous teeth erupt, had an increased risk of dental caries. This may be due to other factors which are linked with prolonged breastfeeding including nocturnal feeding during sleep, cariogenic foods/drinks in the diet or inadequate oral hygiene practices. Further research with careful control of pertinent confounding factors is needed to elucidate this issue and better inform infant feeding guidelines.