Bisphenol A: Quietly Crumbles The Tooth Enamel

5. August 2013
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The plasticiser Bisphenol A (BPA) appears to be a real devil's tool. Now, scientists have been able to show that it can also damage tooth enamel permanently and irreversibly.

Bisphenol A (BPA) is manufactured worldwide in large quantities. It manages to pass into the human body mainly through food whose packaging contains the compound. Plastic cans and beverage containers made of plastic, but also food tins and metal beverage cans, contain bisphenol A. In the human body it seems that this ubiquitous chemical acts even at low concentrations similarly to oestrogens. BPA could be (co)responsible for developmental disorders, neurological damage, a weak immune system, increased cancer risks (especially for breast cancer), behavioral problems, infertility in men, obesity, diabetes and cardiovascular problems, in summarising what scientists presently suspect and are discussing. Sustained weakened tooth enamel could now be added to this list, because especially within the first months of life, during the formation of enamel, children are particularly vulnerable to the effects of BPA and the concentrations of it in their bodies are high, French researchers report.

Brittle, stained and sensitive to pain

Molar incisor hypomineralisation (MIH) is a mineralisation disorder of the permanent incisors and the first permanent molars in the upper and lower jaw. The upper incisors are more frequently affected than the lower ones. An instance of MIH is not something to be overlooked. Those affected have yellowish white to brown discoloration on certain areas of a tooth or on the whole tooth. The darker the colour, the more porous the tooth structure and the greater the risk of posteruptive loss of substance. The hypomineralised enamel compared to the normal version has a lower calcium and phosphorus content and a higher carbon content. The mechanical resistance of the enamel affected is reduced, which can result even under normal masticatory forces in enamel removal. Not infrequently the victims suffer from increased sensitivity to thermal, chemical and mechanical stimuli. When dental care hurts, a vicious circle begins, because neglected oral hygiene leads to tooth decay. During dental treatment, the pain sensitivity of these mostly young patients cannot be significantly improved even using local anesthesia. Affected children suffer during their dentist sessions a great deal.

More and more cases of MIH

According to the Dental Journal of Baden-Württemberg, the prevalence of MIH in Germany lies between 0.6% to 5.6%. Depending on the study one finds prevalence rates between 3.6% and 25% – with the statistical trend over time being a generally rising one. The mineralisation phase of tooth crowns, which runs from the 8th month of pregnancy up to the fifth year of age, is greatly disrupted in these teeth. Tooth enamel is like an archive that records the conditions from this period permanently and irrevocably, the researchers write. Scientists suspect that ameloblasts – the specialised cells that form the enamel – are partially and irreversibly destroyed in a case of MIH during this phase.

Causes unclear

What are the causes of MIH? The numerous studies which have been conducted to date all come to the same conclusion: although there are indeed suspicions held, the conclusive etiology of MIH nonetheless remains unclear. Among scientists, up until this time, anoxia during or after birth, chronic obstructive pulmonary disease, early administration of certain antibiotics, elevated levels of dioxins or polychlorinated biphenyl (PCBs) in breast milk, infectious diseases such as diphtheria, scarlet fever, mumps, measles, disturbances in mineral metabolism due to malnutrition, celiac disease and vitamin D hypovitaminosis have been discussed as causes. What’s more multifactorial causes are currently the subject of such discussion. As early as 2004, scientists put forward the assumption that constituent components released from plastic bottles, especially those involved in prolonged pacifier bottle use habits, could have a negative influence on the development of tooth enamel. Now the results of a French study suggest that the plasticiser bisphenol A could actually weaken the tooth enamel in a permanent way. The reasons for research include not only an increasing exposure to BPA and other hormone-like substances, but also the increase of MIH.

EU limit way too high?

The researchers first tested rats on how BPA affects the enamel. They exposed the animals before birth and in the weeks afterwards to BPA concentrations which were lower by a factor of ten than those specified by the EU as the tolerable daily value of 50 micrograms per kilogram of body weight. After one month, 75% of all rats’ teeth were of white discoloration and carrying brittle spots. The scientists investigated the teeth under the microscope; they found that the changes matched exactly those of human teeth with MIH: the enamel had too few minerals and too many organic compounds – in particular proteins.

BPA disrupts protein degradation

On closer examination the cause of the problem reveals itself: the formation process of tooth enamel begins by building a protein structure of the tooth. This is used later as the basis for mineral deposition. If all minerals are in place, the protein backbone is practically obsolete and is broken down again, so that settled tooth enamel can be formed by crystallisation. BPA apparently disrupts this process in rats and humans in the same way: under the influence of BPA, during the first stage the teeth accumulate too many proteins, which cannot be broken down properly in the second stage. Thus they hinder crystallisation – the enamel remains soft and brittle. What exactly BPA triggers at the molecular level is what the scientists want to test next. Although the experiments on rats leaves us little room for doubt, researchers are already working on the final proof that BPA also triggers MIH in humans.

In Germany, on 1 March 2011, the Federal Ministry of Food, Agriculture and Consumer Protection banned BPA in association with baby bottles. The sale of previously manufactured bottles using this material was permitted until the end of May 2011. The use of the plasticiser BPA in many other plastics is also still permitted.

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