Whether an event x – for example the birth of a child – is causally related to a health problem y – such as later tooth loss – could hardly be investigated so far: For practical and ethical reasons, it is not possible to carry out clinical studies with random division into comparison groups, as is the case with many complex health research questions. To solve this problem to some extent, scientists from Heidelberg, Wuppertal, Munich, Worms and Nijmegen (Netherlands) have now transferred statistical methods from econometrics to medical research in a new approach. For example, they wanted to know what is behind the saying “Every child costs a mother a tooth”. After evaluating data from more than 34,000 people from the “Survey of Health, Ageing, and Retirement in Europe”, a data survey conducted in 14 European countries and Israel, they came to the conclusion that the birth of a child can actually lead to an above-average frequency of tooth loss. The results of the evaluation have now been published in the Journal of Epidemiology & Community Health.
“The results of our study show that additional pregnancies tend to have an effect on the oral health of mothers,” explains senior author Prof. Stefan Listl, head of the Translational Health Economics Section at the Department of Dental Conservation at Heidelberg University Hospital. “This is medically plausible. We know, for example, that the risk of gum disease increases during pregnancy. However, our investigations do not allow any conclusions to be drawn about the exact causes of the increased risk of tooth loss. “It is much more important for the researchers to prove that it is possible to approach previously unsolvable epidemiological questions with these statistical tools. “These so-called quasi-experimental methods can be used to investigate causal relationships, even if randomised clinical studies or longitudinal studies are not possible. Especially with regard to oral and dental health, this could be a helpful tool – after all, diseases of the teeth are among the most common chronic diseases worldwide, with serious effects on the quality of life,” says the dentist and economist.
Chance is essential for meaningfulness – but when is a child chance?
In order to find out beyond doubt whether childbearing actually increases the mother’s risk of tooth loss, a comparison with a control group is necessary. In the usual study design, the subjects would be randomly divided into two or more groups: The draw would decide who would remain childless or have one, two or more children. Such a study is not feasible.
The scientists therefore worked with a trick: they searched the extensive data set of the survey for so-called natural random variants, i.e. clues for more or less “randomly formed” children. The first variant is obvious: the comparison of single and twin births. However, the researchers did not find any difference in the number of teeth in mothers aged 50 plus. “It could be that twin mothers are naturally healthier and therefore less susceptible to dental problems,” Listl can imagine. In addition, the team looked at families in which two children of the same sex were followed by a third. It has been statistically proven that this constellation increases the probability of having a third child: Often there is a hope that after two boys they will still get a girl or vice versa. Mothers with two children of different sexes served as a comparison. Here the difference was considerable: In the second half of their lives, mothers with three children had on average around four teeth fewer than mothers with two children.
Conclusion: Keeping an eye on oral health during pregnancy
What benefits can expectant mothers derive from these results despite all the limitations? “Be aware of the risk, pay attention to careful oral hygiene during pregnancy and go to the dentist regularly,” advises Listl. By the way, the researchers also checked the fathers’ teeth. Here they found no correlation between the number of children and the number of teeth.
Literatur:Gabel F, Jürges H, Kruk KE, Listl S. et al. Gain a child, lose a tooth? Using natural experiments to distinguish between fact and fiction. J Epidemiol Community Health Published Online First: 13 March 2018. doi: 10.1136/jech-2017-210210