The teeth represent the real black box of the organism

Saturday 27 February 2016
For the last two years, Marina Martínez de Pinillos, a researcher in the Dental Anthropology Group at the National Centre for Research on Human Evolution (CENIEH), has been involved in the collection and classification of milk teeth from different places in Spain. Her objective, as she reveals in this interview, is clear: to create the largest record of deciduous dentition in the world.

Why does CENIEH claim that this register of milk teeth is "unique in the world"?

-It is not the only record of human dentition in the world, but it is the largest in terms of teeth from immature individuals, i.e. milk teeth, from which, in addition, we know the sex and age of the individuals, something unusual but very valuable for carrying out research on dental development patterns, demographic studies or sexual dimorphism, among others.

How did the idea of creating this register of teeth come about?

-In the Dental Anthropology Group we had been thinking for some time about having a significant collection of deciduous teeth. Talking with the head of the Scientific Culture and Innovation Unit at CENIEH, Chitina Moreno Torres, the idea arose of organising a campaign to collect teeth with the collaboration of the public, and thus involve society in the scientific projects carried out at CENIEH. This initiative was joined by the Casita Museo de Ratón Pérez in Madrid, which had a notable influence on social participation. My intervention in this project was, firstly, to encourage society to collaborate in an initiative as important as this one for the scientific community. And then, to be present at the collection of teeth and, with the help of other colleagues, to correctly classify each of the teeth that were handed in to us.

How was the collection of teeth carried out and what response have you had from society?

-Anyone, both adults and children, who wanted to donate their teeth could do so by coming to CENIEH during the 6th European Researchers' Night, where they not only contributed their grain of sand to scientific progress, but also had the opportunity to participate in the workshops and informative activities that took place at the research centre on the occasion of this event.

Society's response to this initiative has been much better than expected. Our expectations have been far exceeded and, in fact, we continue to receive dental pieces from children from different parts of Spain who send them to us by post or who come to the centre to leave them in person.

How many teeth have been collected so far?

-So far, we have collected around a thousand teeth, mostly deciduous teeth, but also adult teeth that will also be useful for different studies and research that we are carrying out.

Why are so many teeth necessary?

-The first thing to know is that the cells responsible for forming enamel and dentine -ameloblasts and odontoblasts, respectively- secrete a series of organic substances that eventually mineralise and make teeth the hardest tissue in the body, allowing them to be almost perfectly preserved after the death of a living being. This is why teeth are fundamental in the field of Palaeoanthropology, where the fossil record is very scarce, but also in the field of Forensic Sciences, especially in cases where the body has suffered serious alterations. Therefore, having an extensive record of dental pieces is very important for the scientific community.

Why only deciduous teeth? Aren't adult teeth, such as those extracted in a dental practice, for example, just as important?

-Since most of the time deciduous teeth are discarded, the ultimate goal of this project was to collect them to form an important comparative collection and reference study to create a large database that could be used by scientists in all fields. However, during the two collection campaigns, adult teeth were also brought to us, which we have also incorporated into our database and which provide us with very valuable information. The most common problem or what usually happens with the teeth extracted in dental surgeries is that, most of the time, they are removed because they are in poor condition or pathological, which makes it impossible to carry out many of the investigations we do in the Dental Anthropology Group.

Is there any kind of record of adult teeth similar to the one you have created at CENIEH?

-There are different collections of permanent teeth, both fossil teeth and those belonging to modern populations. Normally these collections come from different sites (in the case of fossil samples) or from cemeteries, dental clinics or forensic anatomical institutes (in the case of the modern population). However, in most of these records the sex and age of the individual is unknown, and must be estimated using other techniques that are usually associated with an error and, therefore, are less precise and, in many cases, insufficient to obtain the information necessary to carry out subsequent studies.

The transcendence of our collection is that it is associated with a database in which we have noted both the age at which the tooth fell out and the sex of the individual through the information provided by the owners at the time of delivery of the tooth. In other words, we know with certainty when each tooth fell out and to whom it belongs.

What studies and research will these teeth be useful for?

-From the Dental Anthropology Group of CENIEH we are carrying out different research related to the dentition of Pliocene and Pleistocene hominids with interest in the taxonomy, phylogeny, development and evolutionary scenario of these species. Within these studies we highlight research on the external (enamel) and internal (dentine and pulp cavity) morphological characterisation of teeth using computerised axial microtomography (microCT) techniques.

We also carry out studies on the pathologies suffered by extinct human populations, with interest not only in their health and disease status, but also in their relationship with the behaviour and degree of ecological adaptation of these populations.

We are also conducting research on the pattern of dental development and histology, as well as studies of sexual dimorphism in Pliocene and Pleistocene hominids. All this research has a direct impact on the definition of the life history model of extinct populations. For this reason, it is very important to have a good current reference collection, such as the one we are creating, which serves as a comparison when carrying out numerous investigations, not only in the field of Palaeontology but also in other sciences such as Forensic Odontology or Dental Anthropology.

Marina Martínez de Pinillos,investigadora del Grupo de Antropología Dental del CENIEH
Marina Martínez de Pinillos,investigadora del Grupo de Antropología Dental del CENIEH.

What information can a tooth reveal?

-Because of the hardness of their tissues, teeth represent the real "black box" of the organism. They reflect many of the events we go through during our lives. For example, dental morphology perfectly reflects the type of diet and the ecological niche in which a species develops. Simplistically, we could say that each species has a characteristic type of tooth shape and size, which is very useful for taxonomic studies (recognition and classification of species, genera, families, etc.) and phylogenetic relationships.

Through dentition we can also estimate the age at death of an individual. These results will be much more accurate if we are dealing with immature individuals since, as we know, teeth erupt at certain ages. However, sometimes this eruption is conditioned by circumstances outside the natural biological cycle (malnutrition, lack of space, etc.), which can lead to a significant variation in time.

Likewise, we can know how long it has taken for a tooth to form. It is known that enamel and dentine grow in a discontinuous and circadian manner, i.e. the cells responsible for forming these tissues (ameloblasts and odontoblasts) secrete these substances intermittently. This secretion occurs during part of the day and stops during the rest of the day, generating a series of microscopic striations in the enamel and dentine. In addition, after approximately seven to nine days, the secretion process stops again and Retzius striae (on the enamel) and Owen's lines (on the dentine) are formed. This discontinuous form of growth allows us to know precisely how long it has taken for a tooth to form. By simply counting the striae, we can know the number of days it has taken to form. Thanks to these studies, important research is currently being carried out on the pattern of dental development in extinct populations.

What technological advances have enabled the development of Dental Anthropology and Forensic Odontology?

-In recent years there have been great technological advances in the field of microscopy. On the one hand, the environmental scanning electron microscope (ESEM) makes it possible to obtain very high resolution images of the external surface of the tooth. On the other hand, with the non-destructive technique of computerised axial microtomography (microCT), based on X-ray detection, we obtain virtual micron-thick slices that allow us to access the internal structures of the teeth and subsequently carry out highly accurate three-dimensional virtual reconstructions using sophisticated and complex highly specialised computer programmes. Therefore, thanks to the use of these new techniques in the field of Palaeoanthropology, we are defining new qualitative and quantitative variables that are allowing us to obtain more and more valuable data on the dental apparatus of human populations.

How has the shape and jaw evolved in Homo sapiens?

-The masticatory apparatus, like other skeletal structures, has undergone complex modification during the evolutionary process. Over time, these changes have been associated not only with the growth of the cranial vault, but also with adaptations to different food diets and changes in the ecosystems whose environments provided the products for survival. The growth of the mandible and maxilla depends on the biomechanical stimulation associated with the chewing forces required to process food. Thus, the evolution of the dental apparatus in the jaw has tended towards reduction and simplification. Both the mandible and maxilla and their teeth have become more gracile, i.e. less powerful, designed for a type of diet that is easier to process. If we compare our dentition with that of other species, such as Neanderthals, or even with other genera, such as Australopithecus, we can clearly see how the mandible is much less robust and the teeth are smaller (elimination of accessory cusps, absence of labial convexity, etc.) and present simpler morphologies, with a smaller number of complex dental structures (crests, cingulae, accessory tubercles, etc.). In general, dental reduction, in terms of reduction in size, and simplification of structures has been the basic evolutionary trend in the dental system of Homo sapiens.

Can we predict how it will continue to evolve?

-For an anatomical element to evolve, a number of conditions must be met, the main one being that it affects the reproductive capacity of the individual. Today, unlike in previous species, the deficiencies that can arise in our masticatory apparatus do not limit our ability to feed ourselves and are therefore not so decisive for our survival. This means that these anatomical structures are not exposed to such strong selective pressure as was the case with our ancestors. It is therefore difficult to determine the evolutionary changes that may occur in the dentition, as they do not respond to natural selection processes but rather to random changes such as genetic mutations. An example known to all is the so-called dental agenesis or lack of teeth, the most common today being the disappearance of the third molar or wisdom tooth.