Extrinsic black tooth stain and dental caries in the primary dentition of Vietnamese preschool children.

PURPOSE: To assess the association between extrinsic black tooth stain and dental caries experience in the primary dentition of preschool children in Hue, Vietnam. METHODS: A cross-sectional study was conducted among preschool children aged 3-5 years in Hue, Vietnam. Black stain was diagnosed using standardised clinical criteria and classified as mild, moderate, or severe. Dental caries experience was assessed using the decayed, missing and filled primary teeth (dmft) index. The dmft scores were compared between children with and without black stain using the Mann-Whitney U test. An exploratory Spearman correlation examined dmft in relation to an ordinal black-stain score ranging from absence to increasing severity. RESULTS: Black stain was observed in a relatively small proportion of the participating preschool children during the clinical examination. Median (interquartile range) dmft was lower in children with black stain than in those without [3 (0-6) vs 5 (2-10); p < 0.001], with a small effect size (r = 0.11). The ordinal black-stain score showed a weak inverse correlation with dmft (Spearman's ρ =  - 0.108, p < 0.001). Because the score incorporated both black-stain presence and severity, this correlation did not demonstrate an independent severity-related gradient. CONCLUSION: The presence of black stain was associated with lower caries experience in preschool children, although the magnitude of the difference was small. The cross-sectional findings should not be interpreted as evidence of a protective effect of black stain against dental caries and require confirmation in longitudinal studies with adjustment for relevant confounders.