Background Dental diseases are among the most frequent diseases globally and tooth loss imposes a substantial burden on peoples' quality of life. Non-experimental evidence suggests that individuals with more children have more missing teeth than individuals with fewer children, but until now there is no causal evidence for or against this.
Methods Using a Two-Stage Least Squares (2SLS) instrumental variables approach and large-scale cross-sectional data from the Survey of Health, Ageing, and Retirement in Europe (study sample: 34 843 non-institutionalised individuals aged 50+ from 14 European countries and Israel; data were collected in 2013), we investigated the causal relationship between the number of biological children and their parents’ number of missing natural teeth. Thereby, we exploited random natural variation in family size resulting from (i) the birth of multiples vs singletons, and (ii) the sex composition of the two first-born children (increased likelihood of a third child if the two first-born children have the same sex).
Results 2SLS regressions detected a strong causal relationship between the number of children and teeth for women but not for men when an additional birth occurred after the first two children had the same sex. Women then had an average of 4.27 (95% CI: 1.08 to 7.46) fewer teeth than women without an additional birth whose first two children had different sexes.
Conclusions This study provides novel evidence for causal links between the number of children and the number of missing teeth. An additional birth might be detrimental to the mother’s but not the father’s oral health.
- oral health
- instrumental variables
- causal inference
- child bearing
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Contributors The study was conceived by SL. Statistical analyses were designed by KK and FG and undertaken by FG. Interpretation of data was undertaken by FG, KK, HJ and SL. FG and SL produced the initial draft of the manuscript; all authors revised it critically for important intellectual content, approved the final version prepared by FG and SL, and agree to be accountable for all aspects of the work.
Competing interests None declared.
Patient consent Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement The SHARE data are publicly available (http://www.share-project.org/data-access/user-registration.html). The authors of this manuscript are not authorized to provide data directly to any users. STATA code corresponding to this article is available from the first author upon request.
Correction notice This article has been corrected since it published Online First. In the ’Results from regression analysis' section, the sentence "[… ] men have an average of 0.24 (95%-CI: –0.53 to 0.05) fewer teeth if their first two children had the same sex instead of different sexes; and men have an average of 0.01 (95%-CI: –1.26 to 1.23) fewer teeth if they had a multiple birth instead of the birth of a singleton." has been corrected to "[… ] men have an average of 0.24 (95%-CI: –0.53 to 0.05) fewer missing teeth if their first two children had the same sex instead of different sexes; and men have an average of 0.01 (95%-CI: –1.26 to 1.23) fewer missing teeth if they had a multiple birth instead of the birth of a singleton. In the Abstract, the sentence "[… ] from 14 European countries and Israel study years: 2015)" was corrected to "[… ] from 14 European countries and Israel; data were collected in 2013)".