The pattern of association between early childhood caries and body mass index in pre-school children within Aotearoa | New Zealand: a national cross-sectional study.

OBJECTIVES: The relationship between childhood anthropometric measurements and dental caries has an inconsistent evidence-base. This study investigated dental caries experience and body mass index (BMI) measurements of children aged 4 years in a national cohort, after accounting for key confounding variables. METHODS: A near whole-population cross-sectional study of children who had a health and developmental assessment, as part of the nationwide B4 School Check screening program, conducted in Aotearoa | New Zealand (ANZ) between 1 July 2010 and 30 June 2021 was studied. The extracted database included 582 820 children, of whom 572 523 (98.2%) had valid BMI and oral health records. Dental caries experience was derived from the 'lift the lip' oral health screening, and measured height and weight were used to calculate sex-specific BMI-for-age z-scores (BMIz). Analyses were adjusted for age, sex, ethnicity and area-level deprivation. Modified Poisson regression models using 2-degree fractional polynomial curves for BMIz were employed. RESULTS: In the extracted sample, the median age was 4.3 years (interquartile range: 4.1-4.5 years), 283 565 (48.7%) were female, 135 734 (23.4%) and 74 237 (12.8%) were identified as Maori and Pacific, respectively, and 140 931 (24.4%) lived in the most deprived areas of ANZ. Overall, 81 926 (14.2%) had dental caries identified. In unadjusted analyses, a significant J-shaped association was observed between dental caries experience and BMIz. However, in the adjusted analysis, a significant flattened S-shaped association was found; those with lower BMIz had lower predicted probabilities of dental caries experience. Large differences in predicted probabilities were observed between different sex, ethnicity and area-level deprivation groups. CONCLUSIONS: This study found significant non-linear associations between dental caries experience and BMI in 4-year-old children. However, the inclusion of confounders importantly changed the shape of this non-linear association. Sex, ethnicity and area-level deprivation inequalities had a greater impact on dental caries experience than BMI.