Secondhand Smoke in Infancy Linked to Childhood Tooth Decay

Laurie Barclay, MD

October 22, 2015

Japanese iInfants who were exposed to tobacco smoke at age 4 months had about twice the risk for dental caries by age 3 years,although the incidence was not significantly related to according to a population-based retrospective cohort study published October 21 in the BMJ. In contrast, the authors found no significant link between childhood caries and maternal smoking during pregnancy.

Although these findings cannot establish causality, they support extending public health and clinical interventions for preventing caries to include reducing secondhand smoke, the study authors say, adding to other established measures such as sugar restriction, oral fluoride supplementation, and fluoride varnish. Dental caries are still found in more than 20% of US children aged 2 to 5 years and in 25% of 3-year-olds in Japan.

"Cross-sectional studies have suggested associations between exposure to secondhand smoke and caries in deciduous [baby] and permanent teeth, but data from cohort studies are limited to one study in Sweden," write Shiro Tanaka, from Kyoto University in Japan, and colleagues.

“Secondhand smoke may directly influence teeth and microorganisms” in the mouth, the authors saywrite. It may cause inflammation in the mouth and promote more disease-causing microorganisms, result in salivary gland and immune dysfunction, and directly affect the formation and mineralization of teeth.

The cohort for this study consisted of 76,920 children born in Kobe City, Japan, between 2004 and 2010 who had municipal health check-ups at birth and at 4, 9, and 18 months and 3 years as well as dental examinations at age 18 months and 3 years.

Parents completed standardized questionnaires on smoking during pregnancy and exposure of infants to secondhand smoke at age 4 months. Caries in deciduous teeth was the primary endpoint, defined as one or more decayed, missing, or filled teeth, determined by qualified dentists without radiographs.

More than half (55.3%) of the children lived in smoking households, and 6.8% had exposure to tobacco smoke. The authors note that children living in smoking households may not have had direct secondhand smoke exposure if the houses had separate smoking areas.

At 3 years (follow-up rate, 91.9%), there were 12,729 incidents of dental caries, most of which were decayed teeth. Risk for caries at age 3 years was 27.6% for children with tobacco smoke exposure, 20.0% for children in smoking households but without evidence of exposure to tobacco smoke, and 14.0% for children in nonsmoking households

Compared with children in nonsmoking households, children in smoking households but without evidence of exposure to tobacco smoke had a propensity score adjusted hazard ratio (aHR) for caries of 1.46 (95% confidence interval [CI], 1.40 - 1.52), and those with tobacco smoke exposure had an aHR of 2.14 (95% CI, 1.99 - 2.29). For maternal smoking during pregnancy vs nonsmoking households, aHR was 1.10 (95% CI, 0.97 - 1.25).

The authors note that limitations of this study include reliance on parental questionnaires, possible confounding uncontrolled variables, the relatively small number of children exposed to smoke only during pregnancy, and limited generalizability to other populations.

The authors have disclosed no relevant financial relationships.

BMJ. 2015;351:h5397. Full text

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