Correlation between siblings in caries in Norway. A quantitative study

Abstract Background The role of the family for caries between siblings has been a focus for researchers for almost 100 years. However, the contribution of the family to the variation in caries has not been determined. Objectives To estimate the correlation between siblings in caries, and to investigate whether this varied according to number of siblings, mother's level of education, marital status and country of birth. Methods The population included families with two or more siblings, altogether 409 766 children and adolescents aged 6–18 years, and 181 551 mothers. Data on caries were from electronic dental journals, which were merged with data from Statistics Norway about the characteristics of the mothers. The analyses were performed using random‐effects regression, in which separate regressions were run for the extent of the carious lesion. Caries was scored for permanent teeth only. Mothers were used to identify siblings within families. The correlation between siblings in caries was measured using the intraclass correlation coefficient. Results The proportion of the variance in the outcome measures that was due to between‐family variability was in the range 13–29%. The intraclass correlation coefficients from the analyses of the subpopulations that described the characteristics of the mothers were fairly similar to the ICC s as estimated on the whole population. Conclusion We identified a fairly strong family effect, which confirms that the family is an important arena in which the dental health of the children is formed. An improvement in dental health for one of the siblings was associated with a positive effect on the dental health of the other sibling, and vice versa.