SOME DENTAL MORPHOLOGICAL CHARACTERISTICS OF IRISH ARCHAEOLOGICAL POPULATIONS: an aid to biological affinity and the origins of the Irish?

Posted on October 4, 2019

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SOME DENTAL MORPHOLOGICAL CHARACTERISTICS OF IRISH ARCHAEOLOGICAL POPULATIONS: an aid to biological affinity and the origins of the Irish?

 

ABSTRACT
The aim of this study is to assess the morphology of some aspects of Irish teeth dating from prehistory to late medieval times. Morphological characteristics of the human body such as pigmentation and facial form are used by many researchers as an anthropological measure to research such as evolution and the comparison of populations. Teeth have less noticeable characteristics but are an extremely useful tool. Variations on tooth shape have been recorded for 1508 molar teeth from Irish archaeological assemblages as part of this survey. This may contribute to our knowledge on the origins of the Irish. Two types of anomalies are outlined here, the Cervical Projection of Enamel (CEP) and the Enamel Pearl (EP).

INTRODUCTION
The island of Ireland is located in north-western Europe, in the North Atlantic Ocean. The origins of the inhabitants of Ireland, has had a considerable amount of debate over the years. There is no simple answer but it no doubt has multiple origins. Many groups of humans have arrived on the island on the rim of the continent of Europe over its thousands of years of occupation. European culture has left its influence in many ways such as language, religion, art, industry etc. It is reasonable to assume that genes too have left their impression. The close proximity of the island immediately located to Ireland’s east, Britain, has also resulted in considerable interaction. Mallory (2013) contends that the origin of the Irish is likely to be a mixture of a number of populations starting with Iberia, and combined with some genes from the Near East.

The human tooth is an excellent tool, whose examination can be used by a range of specialists, including anthropologists, geneticists, and palaeontologists, to provide invaluable information on familial, racial, and the evolutionary affinities of people (Brabant & Twiesselmann, 1964). Teeth are crucial to the survival of humankind and play a significant part in adaptation to the environment and consequently the evolution of humans. They have also been used in discussions on palaeodemographic discourses, including migration, population sizes as well as changes in culture, technology etc.

A tooth is a hard structure firmly fixed in a socket in the upper or lower human jaw. The crown is the part of the tooth which appears in the mouth, and the part which lies hidden beneath the gum and other investing structures is the root. The line or junction between the crown and the root is termed the cervical margin. The crown has the potential to provide a tremendous amount of morphological information. Each adult individual has 32 teeth, of which twelve are molars, six maxillary, and six mandibular. In each quadrant of the jaw there are three molar teeth, first, second and third molars. There are two right and two left sides of the quadrant.

Dental variation occurs within and between families, and also within and between populations. Families and populations are subdivisions of a species comprising individuals who share common biological characteristics. Studies of affinities between family members are a key to this genetic control. In research on living populations, first degree relatives have frequencies of some characteristics six times higher than in the general population. Research to date has resulted in the phylogenetic relationship between populations in many geographic locations. Ireland is ‘an understudied region’ (Cunha et al, 2012), or set of populations. Power (1996, 1997a and 1997b), produced data on dental morphology, when compiling reports on human remains from Irish archaeological excavations. In recent years Weets (2009) engaged in research on a newly described trait, a morphological feature called MMPT (mandibular molar pit-tubercle), examining archaeological specimens from Ireland dating from ‘the Neolithic (circa 4,000-1,800 B.C.) through to the Early Christian period (ca. A.D. 400-1170)’. The examination of the molars for the current study will show how useful this type of dental analysis can be, as part of a multi trait programme combining two dental characteristics. The discipline of dental morphology in Ireland is a field which is deserving of more study.

Interestingly folklore, although obviously not scientific, has always contended that waves of people invaded Ireland in prehistoric times. Folklore involves information on culture handed down verbally or by demonstration.  The Lebor Gabála tells of Ireland being invaded by populations which include the Milesians, Formorians, among others. Archaeological research, such as analysis of weapons, excavation of metallurgical sites, etc has always implied that Ireland is a population with many genetic origins.

DENTAL DEVELOPMENT AND GENETICS

The accuracy of genetic expression is due to the tooth’s highly cosseted developmental environment. Dentitions are secure in their dental follicles during their formation. From initiation through the various stages of the bud, cap, bell, mineralization, and subsequently on to root formation and eruption of teeth, these stages are all under genetic control. On eruption, they are exposed to the environment, and are affected by many factors such as wear, infection and trauma, which can alter crown morphology. Studies of the dentitions of monozygotic and dizygotic twins have been advantageous to research into the aetiological factors responsible for the development of the human dentition, especially if genetic or environmental factors are responsible for dental traits (Higgins et al, 2009). It has been proposed that a single clone of pre-programmed cells leads to the development of every tooth within a certain class (Osborn, 1978). There does not seem to be a specific gene accountable for the development of each cusp, therefore, at a molecular level, all cusps are the same. The longer a cusp remains in its soft tissue stage prior to mineralisation the more likely phenotypic variation will occur because odontogenesis is responsible for a series of complicated epigenetic and morphogenic events.

Enamel, normally confined to the crowns of human teeth, may be found ectopically on the root, either as enamel pearls or as interradicular extensions of enamel.

 

DENTAL CHARACTERISTICS IN POPULATIONS

A study by Cassidy et al (2016) examined DNA samples from a small number of Bronze Age (2026–1534 calibrated BC) skeletons uncovered in a burial ground on Rathlin Island, off County Antrim. This was the same skeletal collection, which the author, had examined and was published, as an addendum to a report on the archaeological excavation of the burial ground (Power, 2000). The author suggested affinity such as family between small numbers of skeletons based on the presence of similar dental characteristics in three of the five individuals with dental remains. The author had also indicated that the dental characteristic had their origin in the east of Asia, and were once known as Mongoloid (from Mongolia) dental traits. This is somewhat similar to the suggestion by Cassidy et al (2016) that the DNA samples from Ireland have a Siberian origin. During the third millennium there was much turmoil in Asia and Europe, and these people may have been displaced, then headed west and ending up in Europe (O’Brien, 2012). They may have brought with them Indo-European languages, including Celtic. The DNA of the Irish during the Bronze Age has similar haplotypes (groups of genes) (Cassidy et al, 2016) to modern Irish, Scottish, and Welsh populations. Also evident in the Bronze Age people are several important genetic variants that nowadays display very high frequencies in Ireland including lactase persistence, blue eye colour, and the haemochromatosis C282Y allele.

Due to the genetic determination of crown and root traits, studies of past relationships between populations ranging from a few generations to 20,000 years ago are possible (Turner, 1982). The Chinese population shows high frequencies of the pronounced shape of shovelling, whereas in Polynesia the opposite is the case. Europeans are more often characterised by the absence or rarity of traits, rather than by their presence. Scott and Turner (1988) in an overview of European collections, indicate that the dental remains are characterized by simple morphology, without many of the usual much studied non-metric traits, such as the shovel-shaped incisor, the presence of another trait called the cusp of Carabelli, etc. Morphological traits take several different forms, such as marginal ridges, extensions of enamel and pearls, etc. When a single dental trait is multiplied by many independent dental characteristics, these comparisons produce significant information on the affinities between individuals, and consequently groups in the past and present. However, much more research needs to be carried out in the discipline of Ireland’s dental morphology. The study which is outlined here represents only (as in the adage) ‘a scratch on the enamel surface’.

THE DENTAL TRAITS USED IN THIS STUDY: ENAMEL VARIATIONS.

Two dental variations, the enamel pearl and the enamel projection/extension are thought to be the result of abnormalities in embryological development. Consensus has not yet been made on their genetic relationship. They are one of a number of the ‘so-called ‘Mongoloid’ (Asian) dental characteristics found in Europe in prehistoric and medieval times (Brabant and Twiesselmann, 1964), more commonly found in Asian teeth, than in Caucasian. Other variations include the better known ‘shovel-shaped incisor’ and the lesser known pits on the enamel of the crown etc. The enamel pearl was first described by Linderer and Linderer in 1842, (Risne, 1974). Moskow et al (1990) found that enamel pearls on permanent molar teeth have an incidence rate of between 1.1%-9.7% with distinct differences among racial and national groups. The total prevalence of enamel pearls was 0.82% (375 teeth) in an examination of 45,785 teeth in a human tooth bank in Brazil (Chrcanovic, 2010). Data does not exist documenting these features in archaeological teeth from the island of Ireland. The aim of this study is to identify this expression in Irish molars.

The enamel pearl has been described as a droplet of enamel, an enameloma, a nodule, and an exostosis. The other enamel anomaly investigated in this study is the interradicular extension of enamel or projection. Most enamel anomalies are composed only of enamel, which is similar in structure to the enamel in the crown. Some pearls consist of hypomineralized areas. However, some also consist of dentine and a pulp horn extending from the pulp in the crown or root, hence forming a firm union with the tooth. When it is developed like this, it may in fact be a remnant of an accessory cusp.

The enamel pearl occurs most frequently on the interradicular area of the tooth (Risnes, 1974b; Sreedevi et al, 2012). One etiological factor which may be responsible for the localized development of the enamel anomaly is the activity of a remnant of Hertwig’s epithelial root sheath, which remains on the root surface during the development of the root, undergoing an enamel producing function. These enamel variations are found only on multi-rooted teeth. They have a tendency to occur on the maxillary teeth (particularly the second and third molars), below the cement enamel junction and at the bifurcation of the lingual and distobuccal roots. When occurring on the mandibular teeth, they are present on the buccal or lingual surfaces. They are rarely found on single-rooted teeth. Risnes, (1974a) studied 8,854 extracted molars in Norway and reported that 2.28% displayed enamel pearls. A higher prevalence of enamel pearls was recorded by Pederson (1949) in Inuit (9.7%) than in other populations.

Initial research, carried out in the first half of the twentieth century, on dental traits focused on the origins and evolution of modern humans, particularly on comparisons between humans (Homo Sapiens) and Neanderthals. These studies concentrated on the anterior teeth. More recent research has emphasised comparisons of the entire dentition. Further research was carried out by researchers such as Larsen (2002) on the ancestry of contemporary groups as well as archaeological populations. Kanazawa and Matsuno (2012) observed that a unique set of dental characteristics existed on Papua New Guineans, which they concluded were acquired from original Australian types of dental features mixing with South Asian and Pacific populations. Christy Turner II’s (1982) dental morphological research laid the groundwork for future dental morphological research. During the last decade there has been rapid advances in the peopling of the New World literature. The utility of dental morphology in resolving questions of population history is well illustrated by a problem that has concerned anthropologists for decades: the origins of Native Americans. It was argued that American Indians were most closely related to Asian populations; one biological feature used to support this position was incisor shovelling. Asians and Native Americans expressed this trait in high frequencies and often pronounced degrees, whereas Europeans and Africans were characterized by lower frequencies and slight degrees of trait expression. The analysis of population variation in another trait, three-rooted lower first molars (3RM1), led to a further refinement of knowledge on Native American origins. The peopling of the Pacific was also addressed by Turner through the use of dental morphologic data. However, there is now considerable debate on these studies.

In surveys of Iberian prehistoric populations, there were newly described discrete traits present, including unusual characteristics of the roots of maxillary central incisors (C. Cunha, et al, 2012). There is a relatively large biological distance between the living Jordanian and Western Eurasian groups with whom they share a recent common ancestor. The authors suggest that the Jordanian population has ‘undergone a major genetic drift leading to a distinct dental morphological pattern for this population from the Caucasoid dental pattern over a relatively short time span’.

 

Figure I. An interradicular projection of enamel on the buccal cemento-enamel
margin of the maxillary second right permanent molar (Photography Catryn Power).

METHODS AND MATERIALS

This study was carried out on a sample of teeth recovered from over fifty Irish archaeological sites. The dental remains ranged in date from the Neolithic period up to the nineteenth century AD. Specimens for this survey were derived from collections held in the Irish Antiquities Division of the National Museum in Dublin, the Ulster Museum in Belfast, the Museum of Limerick, the Department of the Environment, Castlewellan, County Down, and the Department of Archaeology, University College Cork. These teeth were examined by one observer, the author, when the data on a wide range of dental information was collected over several years, as part of routine work on physical anthropological and palaeopathological reports.

Each tooth was examined visually, identified, and charted. For inclusion in the study only those teeth with crowns, including cemento enamel margins and root furcations were examined for EPs and CEPs. Only erupted completely formed permanent teeth were examined. Included in the material are whole or partial dentitions and loose teeth. Teeth including crowns are frequently missing post-mortem from archaeological skeletal remains. This can be due to degradation in the soil and other post-mortem damage such as grave digging, plant root growth etc. Details of all unusual morphology (any variation from the normal Caucasian) in the shape of teeth were documented. Information included the age, sex, and archaeological location of each tooth. Only teeth unaffected by wear, pathology, or breakage were scored.  This study uses the simple method of recording the presence or absence of the morphological trait.

Summarized scores are listed in Table I. The relative frequencies of the CEP and EP traits were calculated. Tables 1 and 2 outline the numbers of teeth, according to period and archaeological site, with the characteristics, and the frequencies of each dental trait. The range of frequencies was estimated for pooled groups for each time period. The results from this research are compared with those known for some Europeans, Asians etc. (Tables 1-2).

RESULTS

The number of permanent erupted molar teeth examined was 1508. These molars were from the island of Ireland and dated from the Neolithic period to the 17th/18th centuries AD. The dental remains were derived from several counties throughout the island of Ireland, though all counties were not represented for each period. Each county will no doubt have its own unique movement of populations which will have a bearing on the results in this study. Thirty-eight molars (2.51% of molar teeth present) have enamel anomalies: 2.05% have enamel pearls and 0.46% have cervical enamel extensions.  A sample of 874 (57.95%) of the 1508 molars showed that almost equal numbers (445, or 50.91%) of maxillary and (429, or 49.08%/) of mandibular molars were present and examined for the presence of these two enamel anomalies.

Enamel pearls usually occur singularly. Cervical enamel projections were more commonly found on the buccal/cheek surfaces of teeth in this study, however they were occasionally located on the lingual/tongue surface of the tooth also. Enamel pearls occurred in populations who also have a high frequency of enamel projections. All except two molars from Armagh town had one single pearl per tooth. The individual from Armagh had two enamel pearls on each of two molars. One cervical enamel projection from Dublin was located on the palatal surface of a wisdom tooth. Cervical enamel projections occurred bilaterally, on the right and left sides of the jaw as well, as on the buccal and lingual surfaces of two mandibular second molars in one person from 15th/16th century Tintern, Wexford.

The amount of combined enamel anomalies evident in the Neolithic is 0.73% of all molars examined in this study (Table 1). This may indicate that the simpler shape of the Caucasian molars had been mingled with elements from Asian populations, who brought the ideas of subsistence also. The molars from the Neolithic period came from a wide variety of counties on the island of Ireland. The Neolithic or new stone age reflects the introduction of a new economy, farming of land and animals onto the island of Ireland. All of this innovation in culture is suggestive of much contact with other peoples, and lands. Although new colonies came onto the island of Ireland, or new ideas is a source of considerable debate. Contact with overseas people is evident by the presence of archaeological monuments such as tombs similar to court cairns in Ireland and which are also evident in Britain and France, while passage tombs are known from Britain, France, Iberia, Scandinavia, Germany, as well as the Mediterranean. The dental evidence in this study suggests that new people arrived during the Neolithic, indicated by the presence of a small frequency of Asian dental characteristics, such as the enamel anomalies.

The Bronze Age follows with the second highest percentage (0.66%) of molars with enamel anomalies (Table 1). The molars examined were derived from the upper two-thirds of the island of Ireland. The beginning of the Bronze Age had arrived in Ireland by 2500 BC and many new technologies were introduced such as metallurgy and the construction of hill forts, with evidence such as ornaments, weapons and tools suggesting an elite but war faring group. Abroad climate change may have left good land in short supply and subsequently displaced people followed warfare. The presence of these dental anomalies in the individuals from the Bronze Age is indicative of the inclusion of some morphological elements of people from overseas, such as Asia.

There were no examples of enamel anomalies or Asian elements in the Iron Age suggesting that the populations examined may be indigenous with simple Caucasian tooth morphology. The dental remains examined came from the eastern counties on the island of Ireland.

The Early Medieval Period has the highest percentage (1.45%) of enamel anomalies on these molar teeth. The dental remains examined came from the northern part of the island of Ireland. The higher percentage in the Early Medieval period may be explained by the genes of newcomers entering the island of Ireland in a period, once referred to as ‘the Early Christian Period’. The Early Medieval period or Early Christian period saw another new culture, based on religion. The influence of the new Roman religion is evident on the art on panels of high crosses. These artistic scenes told the illiterate population about Christianity, assisting in the propagation of the religion by a learned elite group who had influence with Europe. Somewhat later in the early medieval period was a time when the Scandinavian Vikings arrived. Urban life and commerce were expanded by the Vikings. Just as previous foreigners assimilated among the Irish people, so too did the Vikings, the Hiberno-Norse. The Vikings would have genetics mixed with Asian features, their ancestors travelling over the millennia across the Northern part of Asia to northern Europe.

In the twelfth century new religious orders started arriving in Ireland, and with them new cultures, ideas and of course people. These orders came from a variety of countries, the Cistercians from France, Dominicans from France via a foundation in Wales. Ireland truly had many genes arriving on the island. By the thirteenth century, there were twenty-four Dominican orders in Ireland and only five of these were Gaelic foundations. Invaders tended to influence specific areas, rather than overwhelm the entire island of Ireland.

There were no examples of enamel anomalies in the molars dating to the Medieval period, suggesting that these individuals were indigenous people with a simple Caucasian dental morphology. The molars examined came from the counties in the south-east of the island of Ireland. The absence of enamel anomalies could also be explained by the presence of populations who arrived in Ireland in the medieval period having European ancestry. Historical information can confirm this. Norman influence can be seen on the environment, in particular in the south-east of the island, by the end of the twelfth century and continued until the mid-fourteenth century AD. This obviously took place along with a continuous stream of new immigrants, some with a mix of English/Welsh genes, and some originally with an earlier French origin. These colonists built castles, roads and towns. Norman families arrived with their entourage, as well as experts on building, architects, masons, etc. By the end of the fifteenth century AD, the Franciscans had arrived, and added ninety religious houses to the landscape. Throughout these centuries there must have been a continuous flow of people between Ireland and Britain, and traffic through Britain from Europe, as well as directly with Europe.

Of the molars in the 16th/18th centuries AD, 1.74% had enamel anomalies. During the sixteenth century AD and continuing until the eighteenth century AD, settlers from Britain, under government schemes, took the land of the Irish, in large colonies or plantations. The larger towns, Waterford, Wexford, Kilkenny, in the south-east of Ireland were popular with the settlers. The frequency of enamel anomalies in this period may be reflective of the incursion of new people into the areas examined.

 

CONCLUSION

This investigation has given some understanding of the biological characterization of dental morphology of the population on the island of Ireland. Tooth morphology can assist in identifying the movement of people from across the globe into the island of Ireland over the centuries. This type of study could assist in identifying the origins of the Irish. Following the examination of two different types of dental characteristics, the enamel anomalies (enamel pearls and interradicular projections of enamel) in 1508 molars, it is evident that important data is achievable. It suggests that over the millennia there have been many newcomers who have arrived in Ireland, and have mixed with the indigenous population. This is comparable to the available archaeological evidence. The local people were typically Caucasian and when new genes were introduced so too were new physical traits, including some from Asia.

These new morphological dental traits were seen in a small number of individuals in the Neolithic and a greater increase of these dental traits in the Bronze Age is indicative of new people and greater contact with outsiders containing Asian dental characteristics. There were no examples of enamel anomalies in the Iron Age or the Medieval period suggesting that the indigenous populations examined in specific areas were of Caucasian origin and had little contact genetically with the newcomers. Alternatively, this may also represent a time when immigrants were primarily of European extraction comprising dental morphology of Caucasian ancestry. The early medieval period and the 16th/18th centuries AD saw an increase in these dental morphological traits representing large numbers of immigrants into the island of Ireland.

 

PERIOD NUMBER OF MOLARS NUMBER OF MOLARS WITH ENAMEL ANOMALIES PERCENTAGE OF MOLARS WITH ENAMEL ANOMALIES
NEOLITHIC   272  2 0.72%
BRONZE AGE   330 10 3.03%
IRON AGE    58   0 0
EARLY MEDIEVAL   489 22 4.49%
MEDIEVAL   130   0 0
16TH-18TH CENTURIES   229   4 1.74%
TOTAL NUMBER OF MOLARS 1508  38 2.52%

Table 1. The number of molars examined, and the number of enamel anomalies detected in Irish archaeological populations employed in this study. *combined left and right sides for each molar.

 

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Table 2. INVENTORY OF ARCHAEOLOGICAL SITES, WHICH HAD SUITABLE MOLAR TEETH FOR INCLUSION IN THIS STUDY.
In order of County.
Armagh Town, County Armagh;
Baunogenasraid, County Carlow;
Poulnabrone, County Clare;
Ballynacorca, Ballynoe, Labbacallee and Moneen, County Cork;
Rathlin Island and St. John’s Point, County Antrim;
Cathedral Hill, County Down;
Glassamucky, County Dublin;
Jerpoint West, County Kilkenny;
Straid, County Londonderry;
St.Mary’s Cathedral, Limerick;
Millockstown, County Louth;
Carrowlisdoonaun and Moyne, County Mayo;
Betaghstown, Fourknocks I and II, Knockast II, Knowth and Martinstown, County Meath;
Gortnacargy and Lahinch, Co. Offaly;
Culleens, County Sligo;
Ardcroney, Ashley Park and Clonmel, County Tipperary;
Dunmisk, County Tyrone;
Great Down and Clonvickilvant, County Westmeath;
Annaghmore, Norrismount and Tintern, County Wexford;
Ballintruer More and Haylands, County Wicklow.

 

 

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