'Gain a child, lose a tooth' is an old wives' tale, suggesting that along with stretch-marks, backache and swollen feet, tooth loss is also a natural side effect of pregnancy.

Now it seems that there may be some truth to this tale, with new research out this week finding women with larger families are more likely to have fewer teeth.

The study, published in the Journal of Epidemiology and Community Health, looked at data from over 120,000 adults aged over 50 living in Europe and Israel.

Normally a full set of adult teeth is made up of 32 teeth, four of those being the wisdom teeth which are often removed during adolescence.

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Using a statistical analysis technique known as "instrumental variables regression", which mimics a randomised control trial, the researchers found women who had three children tended to have four fewer teeth than women who only had two children. The number of teeth the fathers had did not correlate to the number of children they had, implying having children is only detrimental to the mouth of a mother.

This study ties in well with previous studies that link pregnancy to dental problems. A 2005 study from the International Association for Dental Research looked at more than 2000 pregnant women and found that as the number of children they had increased, so did their risk of periodontal or gum disease, missing teeth and untreated cavities.

From a biological perspective there are many reasons why pregnancy could negatively affect oral health.

Developing babies require a significant amount of calcium to help form their growing skeletons. Some is taken from the mother's calcium stores during pregnancy, most of which is in her bones and teeth.

Pregnancy hormones including calcitriol and parathyroid can also interfere with the absorption of calcium, which may leave the teeth and bones of the mother vulnerable if she isn't ingesting enough calcium from her food.

Pregnancy also seems to increase the occurrence of gum inflammation, also known as gingivitis.

Although scientists don't fully understand the process, it is thought the huge increase in hormones including estrogen and progesterone during pregnancy may increase blood flow to the gums, causing them to swell and be inflamed.

Studies have shown pregnancy results in several changes to gum tissue including an increase in periodontal pockets — spaces where the gums contact the tooth. These spaces can harbour bacteria, which can increase the risk of more complicated dental infections. Left untreated, these can necessitate tooth removal.

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Swollen, irritable gums and increased periodontal pockets can also lead to teeth wobbling more within their bony socket — potentially allowing more bacteria to get in, and again increasing the risk of gum disease and infection.

Another theory is that pregnancy can cause cravings, which may result in women eating more sugary or acidic foods. These can also lead to cavities and tooth loss if left untreated.

Anecdotally, busy mothers with multiple children may also find less time to visit the dentist regularly for preventative treatment, another factor that can increase the chance of tooth removal being needed in the long run.

The study found that as the education level of the woman increased, so did her chance of keeping more teeth.

Although the study looked at a relatively narrow group of people, with an interest in parents who had twins and triplets, it raises questions around whether introducing policies that promote enhanced oral hygiene, increased education around mouth care as well as encouraged regular dental attendance to pregnant and recent mothers should be included in our long term health policy.