Investigation of the relationship of craniometrics and dental anomalies

CONTENTS

I. Introduction

II. Literature Review
Basis of human craniometric variation
Craniofacial development
Development of the masticatory complex
Environment, heredity, and craniofacial development
Occlusal variation and dental anomalies

III. Materials and Methods
Materials
Methods
Statistical Analysis

IV. Results
Relationships between anomalies
Preliminary craniometric analysis
Relationships between dental anomalies and craniometrics

V. Discussion
Palaeoepidemiology and dental anomalies
Dental anomalies and craniometrics
Heredity, population variation and dental anomalies
Arch dimensions and the aetiology of dental anomalies

VI. Conclusion

References

Appendices follow page

List of figures and tables.

Figure 1. Supplemental tooth

Figure 2. Rotated tooth

Figure 3. Peg-shaped M3

Figure 4. Heterotopic M3

Figure 5. Graph of TFI by population

Figure 6. Graph of CBHI by population

Figure 7. Boxplot, BCDL and rotations

Figure 8. Boxplot, HAR and rotations

Figure 9. Rotations and TFI, English

Figure 10. Rotations and TFI, Macedonian

Table 1. Heritability estimates

Table 2. Collection summary

Table 3. Paired landmarks

Table 4. Anomaly distribution by sex

Table 5. Anomalies by population

Table 6. Significant differences, means

Table 7. Craniometric means, anomalies

Table 8. Craniometric means, crowding

Table 10. Indices means, normal skulls

Table 9. Cranial means, normal skulls

Table 11. New indices means, normal skulls

I. Introduction

Summary

The aetiology and epidemiology of dental anomalies of shape, number, and position have significant contributions in the orthodontic clinical literature, and the heritability and variation of the human skull is a major concern of anthropology, but there appears to be little research into the relationship of these dental anomalies with cranial morphological variation. Anthropologists have had a tendency to regard specific nonmetric traits, such as Carabelli’s cusp, and tooth crown metrics in studies of human variation and population distance (Scott 1988; Turner and Scott 2008), and have clarified the effects of developmental plasticity and homoplasy on such studies (von Cramon-Taubadel 2009b, 2011). The study of dental anomalies has been limited to case descriptions and only rarely mentioned in regard to demographics or relationship to morphological variation. Such analyses may not only contribute to anthropological studies of human phenotypic variation, but may help to further elucidate the multifactorial and complex aetiology of dental anomalies.

This project investigated whether there exists a relationship between variation in the size and shape of the skull and pathological dental anomalies of position, shape, and number. By examining several premodern population samples from two different geographical areas, as well as comparing variation at the local level, the research analysed the differences between normal skulls and skulls expressing dental anomalies and occlusal disorders.

Research Questions

The shape and size of the human skull is largely under genetic control but highly affected by the environment, while tooth morphology is more strictly determined by genetics. Numerous studies have associated cranial morphological variation as well as metric and nonmetric dental morphology with global migrations and genetic distance; few, however, have investigated the relationship between craniometrics and occlusal and dental variation. This project examined whether the variation in skull shape, through population distance or admixture (gene flow) or the environment (including diet), in turn affects the likelihood of nonmetric dental anomalies due to spatial changes in the masticatory complex. Further:

- Can the shape or size of the dental arch relative to the size of other cranial components contribute to dental anomalies?
- If so, are these morphological changes based on individual or population variation?
- Is population-based phenotypic variation a contributor to occlusal and dental disorders?
- Do non-syndromic dental anomalies show population variation unrelated to phenotypic variation, suggesting a more heritable component to dental anomalies?
- Is the expression of dental anomalies in congenital syndromes the result of changes to skull morphology?

Aims and Objectives

The aim is to further elucidate the aetiology of pathological dental anomalies and to bring the subject into an anthropological and archaeological context by applying a comprehensive review of the clinical literature to the analysis of archaeological populations. Anthropologically, such data may contribute to the further understanding of the interaction of genetics with the environment to produce human phenotypic variation, and the evolution and adaptation of the modern human masticatory apparatus.

Among the Objectives is the exploration of the relationship between morphologically variable functional complexes of the skull and face with the dentition, and investigating whether craniometric morphological changes lead to changes in frequencies or occurrence of dental anomalies, thus supporting or contradicting proposed theories of the aetiology of these dental anomalies.

II. Literature Review

Basis of Human Craniometric Variation

Change in the shape and size of the skull has been a hallmark of human evolution; a trajectory toward an expanded braincase and a less prognathic, smaller face has been a distinguishing feature of anatomically modern Homo sapiens (Lieberman et al 2002). The anteroposteriorly shortened and superoinferiorly heightened face has been hypothesized to have been a result of the increased maturation period in modern humans, the final globular shape of the adult human skull a response to increasing brain size (Bogin 2003; McBratney-Owen and Lieberman 2003). Despite the long evolutionary history of the expanding cranial vault in humans, and the clear pattern of craniofacial change from earlier hominoids, there has been continuing debate regarding the extent to which the changes are primarily genetic or environmental (Relethford 1994, 2004; Ackermann and Cheverud 2004; Roseman 2004; Roseman and Weaver 2007; Betti et al 2009, 2010). Significantly, the variation in craniometrics between modern human populations often exceeds that of the variation between species of many non-human primates (Strand Vidarsdóttir and O’Higgins 2003) and this craniometric variation has been used for decades in assessing population affinities.

The size and shape of the skull is largely polygenetic, and formed from the interaction of developmental plastic functional complexes with the environment within the constraints and parameters of genetic inheritance (Moss 1997a; Hallgrimssona et al 2007; Martínez-Abadías et al 2009, 2011), and adult skull dimensions are the result of the interplay between several functional complexes (see below; Moss and Young 1960; Moss 1997a; Bastir and Rosas 2005; Sardi and Ramírez Rozzi 2007). Thus it has been argued that geographic and climatic conditions are responsible for cranial shape rather than pure genetics (Relethford 2004; Betti et al 2009, 2010) although more recent studies have supported a more direct relationship between heredity and craniometrics (von Cramon-Taubadel and Smith 2012).

In a seminal work, Moss and Young stated “[t]he form of the skull is related to its functions … Cranial form closely reflects the functional demands of [the] soft tissues throughout life” (1960:281; emphasis in original). They went on to divide the skull into two main components, the neurocranium and the face. While still the result of evolutionary selective pressures, Moss and Young (1960:290) emphasized that the skeletal response is ‘secondary’ and compensatory to changes in surrounding soft tissue. Although an early reading of the description of Moss’ Functional Matrix Hypothesis (FMH) leaves little room for the influence of heredity, a later synthesis emphasized the importance of epigenetic theory (Moss 1997b), which refers to the development and transmission of phenotypic features not directly the result of DNA mutations or combinations (Jaenisch and Bird 2003; Jobling et al 2004).

Moss was certainly not the first to recognize the plasticity of the human skull and its responsiveness to environmental change. Since at least the beginning of the 20th century, the effect of climate was recognized as a defining feature of cranial shape, and Boas’ 1912 study of the effect of migration clearly indicated the extent to which a developing living skull adapts to a change in environmental and climatic conditions (Relethford 2004; González-José et al 2005). Boas’ research showed significant divergence in the cranial measurements of American-born and foreign-born Europeans, a significant advancement of the time, but also important in general to warn anthropologists of the inherent adaptability of the skull regardless of the effect of heritability (Relethford 2004; González-José et al 2005).

Moss’ FMH is important for understanding the nature of the plasticity and development of the human cranium, and most research today takes into account the functional modularity of the skull. Research into the ontogeny of craniofacial variation begins with a postulation of Moss’ FMH, that once bone growth has started according to its predetermined genetic plan, the development of the elements are shaped by local extrinsic, as well as other, possibly genetic, factors (Hunt 1998). Not only is an element affected by neuromuscular activity of its functional matrix, but also by the movement or growth of associated elements, compensating for changes in shape to maintain functional integrity (Moss 1960, 1997a; Hunt 1998). Whether a functional module evolves independently or is instead integrated and coevolving with other cranial modules is the subject of recent debate, but the significance of the functional influence of cranial development remains.

Modules may be ‘nested’ for the purposes of analysis; Pucciarelli et al (2006) divided the neurocranium into four distinct subcomplexes (anteroneural, midneural, posteroneural, and otic), and the face into four as well (optic, respiratory, masticatory, and alveolar). Such division according to single functions is not uncommon, but in general there is a zoological tendency toward dividing the cranium into three major functional components, the splanchnocranium (face), chondrocranium (cranial base), and the dermatocranium (essentially the vault) (Kuroe et al 2004; von Cramon-Taubadel 2011a). But von Cramon-Taubadel argued that such a division does not take into account the evolutionary significance of ossification timing (von Cramon-Taubadel 2011a). Earliest ossification areas are thought to be less affected by the environment, the implication being that the early ossification and inability to deform to stress demands is the result of strong genetic control (Lieberman et al 2002; Strand Vidarsdóttir et al 2002; Strand Vidarsdóttir and O’Higgins 2003; Bastir and Rosas 2005; von Cramon-Taubadel 2011a).

Craniofacial Development

Throughout human evolution, the trend toward bipedalism and expanding brain size has left modern humans with a range of craniofacial variability based on the position and orientation of the cranial base and the large, rounded cranial vault, providing global variation by which populations can be assessed, as well as individual variation, although a prolific debate continues over to what extent individual cranial variation is determined by environmental, genetic, and epigenetic contributions (Relethford 2004; González-José et al 2005; Carson 2006; Betti et al 2009, 2010; von Cramon-Taubadel and Smith 2012; among others). Much recent data supports the theory that the bones of the cranial base and cranial vault are under stronger genetic control, and thus more informative in heritability and distance studies, than the bones of the face, which are far more influenced by environmental stress, diet, and other external factors (Lieberman 2000, 2002; Harvati and Weaver 2006; Martínez-Abadías et al 2009).

Facial growth, as emphasised by Enlow (1990) and Enlow and Hans (1996) is the result not only of this phylogenetic shaping of the cranial vault and basicranium, but is responsive and compensatory, which can result in a “normal” or ideal state, or one of malocclusion, if not abnormality. The plasticity of the human face and the continual compensatory development throughout adulthood is the basis for the field of orthodontics, which is concerned with the prevention and treatment of occlusal abnormality caused by individual variation in craniofacial development (Houston and Tulley 1989).

Synopsis of Craniofacial Development

The study of craniofacial growth saw a tremendous amount of change from the 1960s through the 1990s. Once genes were thought to singularly control entire skeletal elements, only to be seen to contribute to a relationship between tension factors and bone response, a much more multifactorial approach, largely based explanations resembling, if not derived from, the Functional Matrix Hypothesis, in which regulatory genes guide tissue through its response to surrounding tissue “input signals” (Enlow and Hans 1996). The timing of the developmental process is integral to responsiveness to environmental input. A prenatal, early ossified element is considered less likely to adapt or respond to stimuli; a number of studies have corroborated that the bones that develop the earliest have the highest heritability rates (Martínez-Abadías et al 2009; von Cramon-Taubadel 2011a). Later development of the cranial vault is largely accomplished through early brain expansion and the responses at sutures and synchondroses; the face, while influenced by this vault expansion and movement, is also affected by the development of associated functional mechanisms, for respiration, language, and diet. (Enlow 1990; Enlow and Hans 1996; Sardi and Rozzi 2007).

By birth the cranial vault consists only of bony plates surrounded by and interconnected by connective tissue, which are displaced away from each other during brain growth, the tension of the strain at the sutures promoting new bone growth (deposition), thus enlarging each of the bones individually (Enlow 1990; Enlow and Hans 1996). Similarly, functional stress from the muscles involved in mastication, respiration, and language further influence growth of the temporals and occipital, causing further displacement of all of the elements of the skull (Houston and Tulley 1989). The outer and inner tables of the skull bones are acted upon independently, the inner tables shaped by the growing brain and the outer tables by the activities of attached muscles; the tables can be pulled apart in such a way as to create sinuses, as in the frontal bone (Houston and Tulley 1989). The expansion of the vault and subsequent growth of the bones of the calvarium displace the elements anterior to it, that is, the bones of the face, the maxilla and the mandible; significant temporal and frontal bone expansion push the orbits medially and vertically toward each other, subsequently reducing the space available for the olfactory complex (and, in evolutionary terms, reducing the snout) as well as for the masticatory complex, creating a shorter, more “rectangular” than “triangular” jaw than is seen in most mammals (Enlow 1996:167).

Development of the Masticatory Complex

An equally important and simultaneous effect of vault expansion in humans is the flexure of the cranial base, hypothesized to be under stronger genetic control than other features of the cranium with an intrinsic relationship to human bipedalism (Houston and Tulley 1989; Havarti and Weaver 2006; Hallgrímsson et al 2007). The growth and movement of the cranial base (away from the mammalian posterior cranium and toward the central floor, allowing the brain to ‘balance’ on the spine in an upright position), particularly growth and movement at the spheno-occipital synchodroses, creates the sphenoidal sinus and pushes the maxilla in an antero-superior direction away from the mandible (Enlow 1990; Houston and Tully 1989). Additionally, a wide cranial base angle will result in a maxilla more anteriorly placed than the mandible, and a small cranial base angle will result in a maxilla posterior relative to the mandible (Cendekiawan et al 2010).

Further alterations occur which significantly affect the human facial plan. The horizontal span of the pharynx increases with the enlargement of the middle cranial fossa, further pushing the maxillary arch, and the mandible continues compensatory growth to match the position of the maxilla (Moss and Rankow 1968; Houston and Tulley 1989; Enlow 1996). This provides the basis for malocclusion, or the range of occlusal variation in humans: the mandible will compensate to the movement and growth of the maxilla to maintain functional efficacy, and if successful, normal occlusion occurs (Enlow 1990; Oyen 1990). As teeth grow and erupt, alveolar remodelling drives maxillary and mandibular growth in the direction of the growing teeth, so that the dental arches are shaped by dental growth and movement; osteoblastic activity strengthens the alveolus during development and eruption of teeth; suckling in infants helps guide masticatory growth by increasing one dimensional stress (Oyen 1990).

While the cranial vault is responding largely to the expansion of the brain (encephalization), the face is not only responding to such growth and displacement, but experiencing a significant amount of stress from functional demands on associated soft tissue from mastication, respiration, olfaction, speech, expression and a number of other activities (Houston and Tulley 1989; Enlow and Hans 1996; Bishara 2001). These environmental and functional stimuli provide variation in individual as well as population-based facial development, a process which continues throughout life (Oyen 1990; Enlow and Hans 1996).

Environment, Heredity, and Craniofacial Development

Diet

The transition from a hunter-gatherer lifestyle to agriculture has been proposed to have caused a significant change in cranial morphology. Gonzalez-Jose et al’s analysis of 18 South American populations of hunter-gatherers and agriculturalists found that economic strategy was a better determiner of masticatory/alveolar morphology than population distance, emphasising the role of plasticity in the human face (Gonzalez-Jose et al 2004). For several decades data has supported the idea of cranial robusticity as a result of ‘hard’ unprocessed diets of hunter-gatherers, and the conversely modern ‘soft’ diets consisting of cooked and processed foods, requiring less force and muscle strain to ingest, result in an increase in cranial gracility “and a general deterioration of dental health” (Paschetta et al 2010:298; Corruccini 1984; Ortner 2003; Varrela 1992). Studies on mice and nonhuman primates have indicated reduction in the size of masticatory elements of the skull on subjects fed a soft diet (Corruccini and Beecher 1982; Killiardis 1986; Lauc et al 2003). In humans many studies by craniometric research into the transition between archaeological hunter-gatherer and farming populations have corroborated the effects of diet change on the masticatory apparatus (Corruccini 1984; Verrala 1992; von Cramon-Taubadel 2011b). Varrela (1992) suggested that general cranial dimensions are affected by changes in diet, not only because of plastic environmental effects, but also due to selective pressures (Varrela 1992:31). Varrela also argued that changes to mandibular growth since the transition to agriculture has contributed to an increase in occlusal variation, an assertion supported by a number of studies on living and historical populations (Lavelle 1973; Harper 1994; González-José et al 2005; von Cramon-Taubadel 2011b).

With the caveat that this technological-cultural shift may have been the result of or coincident with a population admixture or even replacement, confounding craniometric change as evidence of environmental or genetic change, Paschetta et al (2010) attempted to correct for this confounding by using genetically continuous Amerindian populations during a long period that included the agricultural transition from hunter-gatherer lifestyle (Paschetta et al 2010:302). They divided the cranial measurements into the functional complexes of neurocranial, facial, alveolar, masticatory, and mandibular modules, and further divided each of these complexes into distinct morphological components, following the methods of hierarchical functional craniology (Paschetta et al 2010). Their results supported the idea that dietary softness (determined not only by cultural archaeological evidence but dental microwear analysis) can result in reduced growth of elements of the masticatory complex (in this case the attachment of the temporalis muscle, the zygomatic arch, and palate) due to reduced strain “magnitude and/or frequency” (Paschetta et al 2010:308). However, general reduction in whole skull size or relative size of face was not observed in the Ohio Valley samples, suggesting that the plastic effects of diet on craniometrics are localized to specicifc maxillofacial elements rather than general (Paschetta et al 2010:309).

Corruccini referred to modern occlusal variation as part of the epidemiological transition that includes a number of other deleterious health effects of modern lifestyle and diet (Corruccini 1984). According to Ortner (2003:598), “chewing stress stimulates mandibular more than maxillary growth”. Since normal, or ideal, occlusion is dependent on the mandible “catching up” to maxillary growth and movement spurred on by encephalization and basicranial development (Moss and Rankow 1968; Enlow 1996), it is not surprising that modern dietary habits would be implicated as contributing to an increase in dental crowding and occlusal variability in modern human populations: Hillson regarded dental anomalies such as crowding as “so common as to be almost normal” (Hillson 1996:112), although he questioned the validity of a soft diet as being the prime cause of modern occlusal anomalies, considering the range of other environmental and behavioural conditions (such as mouth-breathing) that affect facial position more continuously (Hillson 1996:116).

Environmental and Climatic Effects

Changes in diet, then, are likely not the only influence upon human occlusal variation; environmental variables, particularly climate, have been proposed as a source for craniometric variation, but recent research has found such effects limited to specific areas of the face, such as the area around the nasal aperture, or as a result of extreme cold environments (Roseman 2004; Harvati and Weaver 2006; Betti et al 2009, 2010). If climate does significantly affect craniometrics, it would be expected that genetically distant populations would adapt similarly to similar environments, but a 2009 study of over 6000 skulls from modern populations throughout the world found that climatic signatures are far less significant on craniometrics than those that can be explained by geographic distance from Africa, supporting not only the hypothetical African origin of Homo sapiens, but reflecting the high degree of heritability of cranial morphology (Betti et al 2009, 2010). It is important to note, however, that closely related populations may inhabit, and thus adapt similarly to, similar environments (Betti et al 2010).

Heritability studies

Craniofacial metric variation is continuous and size is responsible for 10 to 36 percent of variation in the shape of the face (Hunter 1990). The continuous variability implies that it is polygenic and facial height may be the result of a variety of factors under genetic control including size of teeth, height of maxilla or mandibular symphyseal height (Hunter 1990:252), all further affected by environmental stimuli. The multifactorial, polygenic nature of craniofacial growth obfuscates the nature of craniofacial variation; even if one gene determined the size and shape of an element, the action of the growth and movement of an associated element, for instance the teeth and muscles acting upon the mandible, the final size of the mandible would appear to be a continuous, polygenetic variable trait (Hunter 1990:245).

Elements susceptible to environmentally-influenced remodelling are plastic and should not only be more variable, but less likely to recapitulate phylogeny and population history; confounding this is homoplasy, which is the morphological similarity of elements of two populations based on similar selective or adaptive pressures from similar environments (von Cramon-Taubadel 2009a). In general, the least variable skeletal traits should have higher heritabilities than such plastic traits.

Penetrance refers to the ability of a gene to be expressed in an individual; that is, the fact that not all individuals who carry a dominant allele will express the phenotype (Pritchard and Korf 2011). Expressivity can be variable as well, meaning that while every individual who may be carrying a specific gene expresses it phenotypically, the range of phenotypic expression varies (Pritchard and Korf 2011). Polygenetic control of a feature, that is the expression of a feature under the control of a number of genes, is more likely to be affected by the environment; not only can environmental variables contribute to the development of polygenetic traits, but some may have a threshold point at which the combination of genes and environmental conditions allow expression (or conversely restrict expression) of the trait (Mossey 1999a; Jobling et al 2004; Pritchard and Korf 2011).

Heritability can be described as the proportion of phenotypic variability that can be attributed to genetic control (Konigsberg 2000; Carson 2006; Pritchard and Korf 2011), and is represented statistically as an estimate, h2, described by the formula:

(1) illustration not visible in this excerpt

in which Va is the sum of genetic variance, Ve total environmental variance, and Vp phenotypic variability (Konigsberg 2000; Carson 2006; Pritchard and Korf 2011). This formula is an estimate of narrow sense heritability, leaving out the effects of dominance, which complicates phenotypic expression but is not transmitted (Konigsberg 2000). The formula for broad sense heritability,

(2) illustration not visible in this excerpt

includes the effects of allelic dominance, Vd; craniometrics, however, is concerned with multivariate, continuous quantitative traits and relies heavily on narrow-sense heritability estimates (Hunter 1990; Konigsberg 2000; Carson 2006).

The h₂ formulae are based on twin studies, and provide a range between 0.0 and 1.0; similarly, r represents a correlation based on estimates of heritability from family studies, ranging from 0.0 to 1.0, in which 1.0 represents total heritability; the expected heritability between a parent and its offspring for any trait can be no more than 0.5, and that of monozygotic twins can be expected to reach 1.0 (Hunter 1990; Townsend et al 2009). Regardless of method, estimating heritability requires genealogical information, and a number of clinical studies have utilized radiographs of patients with known family histories to estimate heritability of craniofacial features (Watnick 1972; Hunter 1990; Harris 2008; Sherwood et al 2008; among others) or archaeological craniometrics on collections with known genealogies, such as the ossuary at Halstatt, Austria, each skull of which is labelled with the name, sex, age, marriage status and family relationships (Carson 2006; Martínez-Abadías et al 2009). Utilizing the Halstett crania, Carson carried out a heritability analysis of standard craniometric dimensions, finding that cranial length measurements tend to be more heritable than breadth measurements (see Table 1), and that overall facial metrics have lower heritability than neurocranial metrics (Carson 2006:177).

Von Cramon-Taubadel (2011a) tested seven “functional developmental modules” (FDMs) for correlations with genetic indicators of heritability, to test the hypothesis that early-forming endochondroses would be more phylogenetically informative than single-function modules (2011a:84). The results of the study, summarized in Table 1 along with a number of other estimated heritabilities, indicated that, among the 15 populations used in the study, the vault was the most directly heritable and the face much less so. This result has been obtained by other studies, some of which indicate that the temporal bone, specifically, is under the strongest genetic control, although in sharp contrast to others (see Table 1; Carson 2006; Betti et al 2009, 2010; von Cramon-Taubadel 2009b). Despite utilizing the same collection, differing results are the result of utilizing different covariates and different individuals (Martínez-Abadías et al 2009). These results generally support the significance of the effects of environment, climate, diet and other external factors that affect the plasticity of the human face and that may be mitigated by geography or cultural variation, as well as the utility of cranial vault shape as indicative of population affinity.

illustration not visible in this excerpt

Table 1. Some published heritability estimates of major cranial elements, regions, or measurements (higher number indicates more likely neutral, that is strongly genetic control over development).

Occlusal Variation and Dental Anomalies

Like the cranial vault and base, the size and shape of teeth have been described as being significantly under genetic control (Doris et al 1981; Dempsey and Townsend 2001; Thesleff 2000; Townsend 2009; Nelson and Ash 2010; Galluccio et al 2012) and “relatively independent” of the genetic factors that guide the development of the rest of the masticatory process (Ortner 2003:598), a result of the ectodermal origin of teeth developing within mesodermal bone (Mossey 1999a). Tooth crowns are formed very early during development, and are less likely to adapt to changing environment, except for the pattern of movement and eruption (Sperber 2006; Ortner 2003), and although acted upon by external stimuli which can result in carious lesions, abrasions, and hypoplasia, teeth cannot remodel (Lycett and Collard 2005). This potential for incongruence may be the initial cause of the theorized increase in occlusal variation and dental anomalies in modern and genetically mixed populations (Mossey 1999a).

Malocclusion, crowding, and impactions

The manner in which the teeth of the maxillary arch meet the teeth of the mandibular arch is the definition of occlusion, although the term is used to indicate a range of meanings related to the closing or use of the jaws (Bishara 2001; Nelson and Ash 2010). Ideal occlusion is one in which the maxillary incisors slightly overlap their mandibular counterparts, the maxillary canines lie in between the mandibular canine and first premolar, and the posterior teeth are matched maxillary cusps for mandibular grooves (Leighton 1991; Hillson 1996; Bishara 2001; Nelson and Ash 2010). As is implied in preceding sections, a normal or ideal occlusion is considered rare in modern, industrialised societies (Hillson 1996; Corruccini 1984). Malocclusions are classified for orthodontic purposes according to severity of misalignment and need for treatment, generally relating to degree or extent of overbite, crossbite, or evidence of crowding (Bishara 2001), that is, divergence from the ideal articulation of teeth. Some researchers have linked malocclusion class with specific anomalies, which may indicate a genetic correlation between malocclusion type and a number of anomalies (Basdra et al 2001).

The environmental and dietary changes consequent of westernisation and urbanization had been thought to be responsible for the reduction in jaw sizes that have led to an increase in third molar impactions, crowding, and other anomalies (Doris et al 1981; Lombardi 1982; Corruccini 1984; Leighton 1991). Lombardi theorized that the selective pressures on the evolution of tooth size have not had time to match the quick changes in diet and compensatory reduction of jaw dimensions in modern populations (Lombardi 1982:38). Corruccini’s 1984 description of malocclusion as a result of the affects of modern society argued against the idea of ethnic mixing or genetic causes for occlusal variation, finding that elements of jaw size, affected by diet and personal behaviour, rather than tooth size causes the discrepancies in the tooth-jaw relationship known in modern societies (Corruccini 1984:425).

In 1996 Hunter argued against popular assumptions that this evolutionary trend in Homo of decreasing mandible size has left little room for the third molar, resulting in other associated anomalies (Hunter 1996). Hunter was concerned that the assumption was often repeated without actual data to support it, in fact going so far as to claim that teeth and jaws are larger in more modern populations (Hunter 1996:263). More recent research has instead supported the original assumption.

Mossey, like Corruccini, saw ethnic mixing as part of the complex of features characteristic of westernisation, in addition to soft diet and environmental pressures, leading to the increase in dental and occlusal variation, and argued that if the jaw cannot grow to accommodate the genetically-determined size of teeth, there must be a threshold beyond which the third molar cannot develop (Mossey 1999a). While Mossey saw the size and shape of teeth and the masticatory complex as largely inherited, he emphasized the polygenetic nature of dental and maxillofacial development thus allowing modifications from environmental pressures, in the aetiology of dental anomalies and malocclusions (Mossey 1999a,b). Based on the idea that gene flow from distant ethnic groups may introduce novel metric variation, he further noted that ethnically “pure” groups are more likely to have ideal occlusion: in the “pure racial stocks, such as the Melanesians of the Philippine islands, malocclusion is almost non-existent” (Mossey 1999b:195).

Harris (2008) explained the pervasiveness of malocclusion and dental anomalies in recent times and in Western nations, agreeing with Corruccini that such occlusal and dental variation is a “disease of civilization” (Corruccini 1984:419). According to Harris, only one in ten “youths” in the United States today has a “naturally occurring good occlusion” (Harris 2008:129). Sceptical of heritability measures, Harris maintained that malocclusions are largely environmental, despite recognizing the high heritability of skeletal arch dimensions and, without significant explanation, claimed that theories of malocclusion as the result of ethnic mixing “have been thoroughly debunked” (Harris 2008:129).

The influence of heritability over occlusion was demonstrated by Normando et al (2011) in their comparison of malocclusion between an indigenous Amazonian population that was the result of a couples’ divergence from an ancestral group, resulting in a high rate of endogamy among the descendents of the new population (Normando et al 2011:1). Because the groups lived in essentially the same environment and ate the same diet, a significant increase in occlusal variation among the new group was interpreted by Normando et al as the result of polygenetic control of craniofacial and occlusal features exaggerated by inbreeding (Normando et al 2011:3). As interethnic mixing may introduce new metric variation or disorders, so endogamy can exaggerate effects of additive polygenic traits by artificially multiplying them (Luac et al 2003; Normando et al 2011). Similar effects of inbreeding were examined by Lauc et al’s 2003 study of an endogamous island Croatian population, in which occlusal variables with high heritabilities, such as overjet, were significantly more common among individuals of consanguineous families than the normal population (Luac et al 2003). Luac et al go on to suggest that the genes responsible for the observed occlusal variations were of little effect, “but extremely numerous”, (Luac et al 2003:307) again pointing to a polygenetic threshold model of inheritance of dental and craniofacial anomalies. Recent studies implicate more than 300 different genes in the dental development (Galluccio et al 2012).

Dental anomalies of shape, position, and number

Significant as a clinical concern, but less frequently investigated as an anthropological subject, is the expression of pathological dental anomalies of shape, position, and number. Among these anomalies is the congenital absence of teeth; ranging from agenesis,anodontia, in which an individual has no teeth; oligodontia, in which the subject is missing more than six teeth; and hypodontia if fewer than six teeth are missing (Bailleul-Forestier et al 2008a; Kouskoura et al 2011), although the term hypodontia is also used generally when at least one tooth is congenitally missing (Kirzioğlu et al 2005; Parkin et al 2009). Hypodontia is the most common dental anomaly in modern humans, and the agenesis of the third molar is by far the most common type (Vastardis 2000; Cellikoglu et al 2011). Although there is evidence for heritability of tooth agenesis, it appears to be multifactorial and is often associated with other anomalous dental structures (Hillson 1996; Vastardis 2000; Brook 2009; Parkin et al 2009; Cellikoglu et al 2011) and reduced tooth size (Brook 2009). Importantly, congenital absence of teeth (or even loss of deciduous teeth) can result in reduction of size of the developing craniofacial structures as well as malpositioning of remaining teeth (Cellikoglu et al 2011). Prevalence of hypodontia varies among the populations of the world, as well as between sexes, and has been reported to be as high as 25% of the population (Brooks 2009). Exclusive of third molar agenesis, prevalence rates seem to range between less than one percent (<1.0%) to over ten percent (>10%), depending on the population (Vastardis 2000; Celikoglu et al 2011).

The expression of extra teeth (beyond the expected complement of 32), either oddly shaped supernumeraries or supplemental, full-sized teeth, is known as hyperdontia. Less frequent in modern populations than hypodontia, hyperdontia includes the additional peg-shaped tooth in between the two central maxillary incisors, the mesiodens, as the most common form (Rajab and Hamdam 2002; Mishra 2011). Non-syndromic supernumerary teeth are associated with larger teeth, tend to be ectopic or impacted, and occur more frequently in males than females (Batra et al 2005; Brook 2009). Hyperdontia not associated with a congenital syndrome are rare; like hypodontia frequencies depend upon population, but range from 0.1% to 3.6% (Batra et al 2005). Although like most dental traits originally believed to be multifactorial and polygenetic, recent research has posited an autosomal dominant trait because of its expression in family pedigrees (Batra et al 2005), but others maintain that specific genes cannot be identified for tooth number anomalies, and suggest a complex aetiology (Galluccio et al 2012).

Supernumeraries have been associated with tooth rotations, in which a tooth erupts at angle divergent from the curve of the dental arch (Rajab and Hamdan 2002). Among the anterior teeth such rotation or ‘winging’ “is so common as to be almost normal” (Hillson 1996:112) and produces an overlap that is characteristic of anterior crowding (Hillson 1996). Rotations have also been described as associated with agenesis of nonadjacent teeth, suggesting a multifactorial but genetic association with other anomalies (Baccetti 1998).

Transpositions, in which two adjacent teeth have ‘switched’ positions, or a tooth erupts in the normal position of a nonadjacent tooth (Ely et al 2006; Papadopoulous et al 2009), also have frequency variations among populations (Chattopadhyay and Srinivas 1996; Ely et al 2006) but general frequency is around 1% (Ely et al 2006) and most commonly occurs in the maxilla (Chattopadhyay and Srinivas 1996; Babacan et al 2008). Most studies posit a multifactorial origin for transpositions, in which epigenetic factors change the path of an erupting tooth (Chattopadhyay and Srinivas 1996; Baccetti 1998; Ely et al 2006).

Dental and occlusal variation in the archaeological and anthropological context

Although the aetiology and epidemiology of dental anomalies of shape, number, and position have significant contributions in the orthodontic clinical literature, and the heritability and variation of the human skull is a major concern of anthropology, there appears to be little research into the relationship of these dental anomalies with cranial morphological variation. Anthropologists have had a tendency to regard specific nonmetric traits, such as Carabelli’s cusp, and metrics in studies of human variation (Scott 1988; Turner and Scott 2008).

For the past decade a good deal of research has provided some answers to the aetiology and epidemiology of supernumerary teeth and hypodontia; the incidence of rotated or reversed teeth, however, seems less investigated and is often aggregated into general categories of malocclusion (Evensen and Øgaard 2007; Ling and Wong 2010). Dental arch dimensions and other occlusal variables have been suggested as causes or aetiologies for rotations, but rotation also appears to occur without associated anomalies, as was reported in the pygmoid Homo sapiens from Flores, Indonesia (Jacob et al 2006). The Flores samples otherwise do not differ significantly from modern human values for dental or craniofacial variables, including arch and tooth dimensions, other than 90° rotated 2nd premolars (Jacob et al 2006).

Non-syndromic supernumerary teeth have been reported and treated since at least as early as the 7_th century AD (Rajab and Hamdam 2002; Duncan 2009), and a number of case reports from prehistoric North America have appeared in the anthropological literature (Ortner 2003), although descriptions extend to as far as far as the Australopithecines (Duncan 2009), and supernumeraries have been recorded in a number of extant and extinct anthropoids (Jungers and Gingerich 1980; Swindler 2002). Legoux (1974) described a number of dental anomalies in a small Final Gravettian population from l’Abri-Pataud, France, the most significant of which are two supernumerary teeth alongside the right upper M2 (17) in one individual and a reversed right upper PM2 (15) in another. He suggested that the rare collection of dental traits among these remains is indicative of a small endogamous population, and proposed a ‘mother/child’ relationship between two of them (Legoux 1974). Similarly, a description of several supernumeraries along with among a small sample from the Mayan site of Ixlú, Guatemala suggested not only the genetic aetiology of hyperdontia but the association with other anomalies, as well as the close relationship of the specimens (Duncan 2009).

Several descriptions of transpositions have been reported from North American sites, 11 cases of canine-first premolar transposition from one Pueblo site in New Mexico (Burnett and Weets 2001), and 7 cases of the same type from prehistoric Santa Cruz island, California (Sholts et al 2010). Assuming transpositions are heritable traits and not the result of occlusal disorder, the high prevalence of such a rare anomaly among one population again suggests small, endogamous populations and inbreeding or close relationships between the individuals with the anomalies (Sholts et al 2010).

Explaining crowding and malocclusions as a result of ethnic mixing and environmental or cultural changes, in which the discrepancy between genetically large teeth and smaller jaw components force the teeth to fit into anomalous positions (Howe et al 1983; Ortner 2003), Ortner described the skull of a child from prehistoric Florida exhibiting small skeletal structure and severe displacement of several teeth “because of inadequate space in the maxilla” (Ortner 2003:602).

The “epidemiologic transition” theory of Corruccini regarding crowding in modern populations was not supported in an assessment of the relationship between medieval and modern dentitions (Harper 1994). Instead, the study found more occlusal variation and anomalies with a medieval sample from a London plague pit. These mediaeval skulls had wider dental arches and shorter arch lengths, and more crowding in the anterior mandibular dentition compared to a modern European sample (Harper 1994). Crowding and irregularity was also found to be common among a Copper Age French site, in which all of the examined skulls expressed anterior maxillary crowding, and several exhibited impacted canines (Mockers et al 2004). The average arch width in this French sample was found to be lower than in modern Caucasians, and the authors argued that the dental irregularities observed are likely the result of “normal-sized teeth erupting in undersized jaws”, following from an “especially sedentary way of life” (Mockers et al 2004:155).

Infracranial Congenital Conditions

Hypodontia and hyperdontia are both commonly attributes of a number of congenital syndromes; the rare occurrence of these anomalies outside of known congenital conditions is consequently referred to specifically as “nonsyndromic dental anomalies.” Although many of these syndromes consist of soft-tissue lesions, a number of the important conditions have been known to affect skeletal structures. Among these syndromes that have been described as leaving skeletal evidence linked with hypodontia are Down syndrome (Trisomy 21), holoprosencephaly, and ectodermal dysplasia; those linked with hyperdontia are Cleidocranial dysplasia (cleidocranial dysostosis), Gardner’s syndrome, and Nance-Horan syndrome (Bailleul-Forestier et al 2008b; Aufderheide and Rodríguez-Martín 1998).

III. Materials and Methods

Materials

To examine the relationship between dental anomalies and craniometrics, a number of complete or mostly complete adult skulls are required. But in order to gauge whether individual variation in the shape or size of cranial components is a result of population variation, a number of populations must be analysed. In addition, each sample must be large enough that one may expect dental anomalies to occur. Such issues are not easy to negotiate with small collections, and using the Biological Anthropology Resource Centre (BARC), University of Bradford, several samples were utilised to represent a mediaeval British population sample, and two collections from the Museum of Macedonia, Skopje, to represent an outgroup from Hellenistic and Mediaeval period Balkans. Summary table of the collections and craniometric data can be found in Appendix A.

A total of 131 individual skulls were selected following a visual examination to determine viability based on the condition of the skull, the facial and masticatory components of the large premodern collections. The specimens chosen were based on considerations of the viability of standard craniometrics and recording of dental anomalies. Sex assessments as recorded for each site were verified by the author following guidelines established by Buistra and Ubelaker (1994).

For the purposes of this study, immature skulls were disregarded because of concern that ontogenetic variability may not represent accurately adult shape, and that the deciduous or mixed dentition may give false results of anomalies number or position. At the initial stage of the investigation, skeletal reports and unpublished documents from BARC were searched for potential useable skulls and feasible archaeological site. Three of the populations (Blackfriars, Box Lane, and Hickleton) are located in Yorkshire, northern England, while Chichester is located in West Sussex, in the far south of England. Craniometric variation has been observed between geographically distant populations due to climate changes and environmental pressures as well as genetics (Howells 1973, 1989; Hanihara 1996; Relethford 2004). While Chichester is located rather distant from Yorkshire, the period of the specimens and their location within England, long after the population transitions of the Romano-British and Anglo-Saxon periods (Russell 2005), make the use of all of the four population samples reasonable to be regarded as an English sample for the sake of sample size.

The English Collections

Blackfriars

Blackfriars was a mediaeval Dominican friary in Gloucester, South Yorkshire, consisting of 192 individuals of the lay population as well as the friars. Of these 192 individual burials, 17 contained reasonably complete skulls. There is evidence that during its occupation between the 13th and 16th centuries the friary may have been used as a hospital based on the types of pathological conditions present in many of the skeletons, although many of the burials indicate a relatively healthy population without a large degree of stress related injuries or osteoarthroses (Blackburn 2010).

Box Lane

Box Lane, a mediaeval cemetery located in Pontrefract, in West Yorkshire, consisting of 88 individual skeletons of which only 9 skulls were suitable for study. The site is of some interest because very few immature remains have been recovered from Box Lane, and among the mostly mature skeletons a number of infracranial traumatic lesions as well as a prevalence of degenerative joint conditions suggest that the population was rural and accustomed to heavy labour (Blackburn 2010).

Hickleton

Hickleton, also in South Yorkshire, a small rural site consisting of 28 adult individuals from the mediaeval to post-mediaeval period, over 800 years of occupation (Stroud 1984); of these only 6 skulls of each sex, most from the medieaval period but several possibly from the 16th and 17th centuries, could be analysed.

Chichester

The Chichester sample was recovered from the cemetery of the St James and St Mary Magdalene hospital, and consists of 354 individual skeletons, largely with leprosy or similar pathological conditions (Magilton et al 2008). 25 male skulls and 11 female skulls were found to be informative for this study, although previously published reports indicate that the collection contains 132 complete skulls (Magilton et al 2008). Despite the use of the hospital as a leprosarium, many of the skeletons are non-pathological and may have originally served as the clerical staff or carers of the hospital (Magilton et al 2008); both pathological and non-pathological skulls were utilized in this project.

The Macedonian Collections

Marvinci

196 skeletons from two locations at Marvinci-Valandovo, southeastern Macedonia, had been excavated throughout the 1980s and represent populations from the prehistoric period, the Hellenistic period, and the Roman era (Veljanovska 2006). Prehistoric remains are very fragmentary and were not suitable for analysis; the skulls used for this analysis were from Antiquity (4th century BC-4th century AD; Veljanovska 2006).

Demir Kapija

Approximately 30km northwest of Marvinci, this largely mediaeval site in the Republic of Macedonia was first excavated in the 1960s and consists of a total 505 burials in a necropolis dating from as early as the pre-Roman period (Valjanovksa 2001). Early Christian era remains were poorly preserved, and this study consists of 28 of the skulls from 305 mediaeval tombs.

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Table 2. Collections summary.

Methods

Standard craniometric variables along with craniofacial indices and ratios were compared between skulls with dental anomalies and normal (no dental anomalous conditions as described below) skulls from the population samples. Statistical analyses tested for significant differences between the groups.

Many orthodontic and clinical studies associate dental anomalies and pathological conditions to malocclusion types, but the nature of archaeological specimens presented the difficulty of matching mandibles correctly to the associated crania accurately enough to make a decision of occlusion type. This has led to the decision to only utilize standard craniometric indices and measurements.

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Table 3. List of cranial landmark measurements.

Craniometrics.

16 standard cranial measurements were taken from the six population samples of complete or near-complete skulls with mandibles, using digital spreading and sliding callipers. The paired landmark measurements are as described by Howell 1973, Buikstra and Ubelaker 1994, and Bass 2005, and are presented in Table 3, above. A number of standard craniometrics (i.e., nasal, orbits) were disregarded due to the likelihood of taphonomic damage and the need to maintain a reasonable sample size. The landmark measurements were chosen to indicate in general the size and shape of the cranial vault, the face, and the masticatory process, and indices and ratios were calculated to gauge relative dimensions (Bass 2005; White et al 2011). Of the measurements chosen, not all could be taken from all skulls; at the very least measurements were taken from skulls that could provide measurements of masticatory features (palate, maxilla, mandible) or cranial features in skulls with analysable dentitions, but missing landmarks of the masticatory elements.

The craniofacial indices, percentage values that gauge breadth to length, used are as follows (Bass 2005):

(1) Cranial Index (CI) = (cranial breadth * 100) / cranial length
(2) Cranial Module (CM) = (length + breadth + height)/3
(3) Cranial Length-Height Index (CLHI) = (cranial height*100)/cranial length
(4) Cranial Breadth-Height Index (CBHI) = (cranial height*100)/maximum cranial breadth
(5) Total Facial Index (TFI) = (facial height * 100)/ bizygomatic breadth
(6) Upper Facial Index (UFI) = (upper facial height * 100)/bizygomatic breadth
(7) Maxilloalveolar Index (MAI)= (maxilloalveolar breadth * 100) /maxilloalveolar length
(8) Palatal Index (PI)= (palatal breadth * 100)/palatal length
In addition, unique indices and ratios will be calculated to determine relative size differences among the craniofacial complexes:
(9) Palatal/Maxillary ratio (PMR): Palatal index divided by maxilloalveolar index (PI/MAI)
(10) TFH/FMT: Index of upper facial breadth (FMT) to total facial height ([TFH*100]/FMT)
(11) UFH/FMT: Index of upper facial breadth to upper facial height ([UFH*100]/FMT)
(12) Jaw breadth index, MAXB/CDL: Index of bicondylar breadth to maxilloalveolar breadth ([MAXB*100]/BCDL)
(13) Mandibular breadth index (cdl/go): Index of bicondylar breadth to bigonial breadth ([BGB*100]/BCDL)
(14) UHTH: Index of upper facial height to total facial height ([NPH*100]/NGN)
(15) FB1: Facial breadth index 1 ([BCDL*100]/ZYB)
(16) FB2: Facial breadth index 2 ([FMT*100]/CDL)
(17) UFI/MAI ratio: Ratio of the maxilloalveolar index relative to the upper facial index, UFI/MAI

Clinical orthodontic literature often measures the dimensions of the dental arch by the use of dental crown traits or cusps as landmarks, but the nature of archaeological samples preclude the use of this method, because of ante- and postmortem loss of teeth. Instead, the dimensions of the masticatory complex will be calculated using the standard craniometrics as described above.

Dental Anomalies.

Visual examination of the dentition determined dental anomalies or significant pathological conditions. Few skulls included a complete dental arch, so placement of the available teeth into the appropriate sockets or examination of socket shape or position (expected, transposed, supernumerary, rotated, etc) as described in Burnett and Weets (2001) and Bass (2005) determined presence of anomalies. The anomalies and disorders investigated:

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Figure 1. Supernumerary mandibular left M3.

Demir Kapija sk.64. Photo courtesy of Dr. Fanica Valjanovksa, Museum of Macedonia.

Supernumerary teeth. Supernumeraries were recorded as supernumerary (not normally shaped) or supplemental (normally shaped), and the mesiodens, the commonest supernumerary. All were recorded as separate phenomena. See figure 1, left.

- Hypodontia. The congenital absence of each expected tooth was recorded, and 3rd molar agenesis regarded independently as well.
- Transposition. Any interchange of normal tooth positions was recorded, or any tooth in an unexpected socket.

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Figure 2. Mildly rotated left mandibular premolars, Hickleton 36.

Rotations and Reversals. Lingually or labially turned teeth will be recorded along with angle, if possible. Includes winging if the winging results in angular rotation. A reversal is a completely rotated tooth, and any occurrence was recorded separately. See figure 2, right.

- Misshapen or peg-shaped teeth, unless supernumerary, were recorded. See figure 3, below.
- Impactions, ectopic and heterotopic eruptions and crowding were recorded and analysed along with anomalies. See figure 4, below.
- Other maxillofacial anomalies, pathological conditions, and infracranial syndromes with dental involvement were noted.

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Figure 3. Peg-shaped left maxillary M3, Chichester 33.

Figure 4. Heterotopic left maxillary M3, Marvinci 316. Photo courtesy of Dr. Fanica Veljanovska, Museum of Macedonia.

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Congenital Syndromes

Evidence for congenital syndromes and dysplasias were recorded, to be analysed separately from normal results.

Statistical Analysis.

The observations described above were recorded onto recording forms, and the data input into an IBM SPSS 18.0 database. The statistical analysis consisted of several steps:

1. Description of the frequency and distribution of the anomalies among the samples, including investigation of associations between anomalies.
2. Description of the significant differences between the craniometrics of the population samples.
3. Investigation of craniometric differences between anomalous and non-anomalous skulls, between sexes and population samples.

Skulls were examined and each possible anomaly was entered as the categorical variables 0, ‘absent’ or 1, ‘present’. Theses variables were tested against each other using chi-square and fisher’s exact tests. Distributions of continuous variables (craniometric variables, indices and ratio variables) were tested for normality and were examined against the categorical anomalies using independent samples t-tests, or Mann-Whitney tests for nonparametric data as appropriate. Other statistical tests are described in text as necessary. All statistics use p>0.05 as not significant, p≤0.05 as significant, and p≤0.01 as highly significant.

The goal of the study is to determine whether the highly heritable elements of the skull, as described in previously published research, are affected by, or conversely affect, the expression of dental anomalies. Because the formation of the dental complex has been argued to be under genetic control independent of the rest of the face (Ortner 2003, among others), and that the environment is significant in determining the shape of the face (Enlow 1990, among others), this project is investigating whether the adult shape and size of the skull (or relative sizes of cranial components) affect the expression of dental anomalies or conversely, that the presence of dental anomalies affect the shape of the face. The null hypothesis is that there is no correlation between dental anomalies and the shape or size of the skull.

IV. Results

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Table 4. Distribution of anomalies by sex. See text.

Frequencies and Distribution of Anomalies

Summary statistics for all anomalies are available in Appendix B, Section 1. Prevalence rates of anomalies are listed in Table 4, above, and divided by population sample in Table 5, below. No significant correlations exist between any anomaly and sex or population. The most common dental disorder among all populations is rotation, at 27.5%, followed by crowding, at almost 24%. Although not statistically significant, prevalence does vary among the populations, with crowding among the Marvinci sample reaching almost 45%, and only around 12% among the Blackfriars sample.

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Table 5. Prevalence of Anomalies by Population Sample.

No cases of any infracranial congenital disorder, such as cleidocranial dysplasia, were observed among any population sample.

Relationships between anomalies

Chi-square and Fisher’s exact tests of the dental anomalies and disorders are summarised in Appendix B, Section 1. Rotations are correlated to crowding among all skulls (χ2=6.37, p=0.012). When analysed by sex, an association for males between rotations and crowding remains (Fisher’s exact test, p=0.032) but is lost for females, and analysed according to geographic population and sex, supplemental teeth were associated with rotations (Fisher’s exact test, p=0.043) and ectopic eruptions were associated with rotations among English males (Fisher’s exact test, p=0.046).

Preliminary Craniometric Analysis

Recorded craniometrics are available in Appendix A, table 1; and summary statistics for craniometric variables are listed in Appendix B, section 2. Sex differences were significant (p<0.05) for all craniometric variables except for palatal breadth (ecm-ecm; t=1.208, p=0.23), therefore all other craniometric variable were analysed separately by sex.

Independent samples t-tests indicated that the most significantly different craniometric variables (p<0.05, see Appendix B, Section 2) were, among females, maximum cranial length (GOL; t=2.813, p=0.007), fronto-zygomatic breadth (FMT; t=2.173, p=0.035), and bicondylar breadth (BCDL; t=-2.133, p=0.040) between English and Macedonian samples. Among males, the most significant differences were upper facial height and bicondylar breadth. However, when normal skulls (no dental anomalies, no crowding) were compared, the significance dropped, although for females maximum cranial length (t=2.066, p=0.052) and for males fronto-zygomatic breath and palatal length were borderline, t=0.801, p=0.050 and t=0.676, p=0.050, respectively.

Among craniometric indices, only cranial module (CM) indicated a significant difference between the sexes (see Appendix B). Independent samples t-tests of the indices showed that the Cranial length-height index (CLHI; t=-1.992, p=0.050) and the palatal index (PI; t=-3.378, p=0.001) are the only significant differences between Macedonian and English samples, but when anomalous skulls were removed the significance was eliminated, except that palatal index remained essentially borderline (t=-1.982, p=0.054).

By far the most significant differences between Macedonian and English sample skulls are in the ratios Upper Facial Height/Total Facial Height (UHTH) and the Facial Breadth ratios. The significance is exaggerated when divided by sex, with UHTH for males reaching p=0.001 (t=-3.776) and FB2 for females, p=0.018 (t=2.517). When anomalous skulls are removed, the significance falls, but FB1 remains highly significant at t=-3.301,p=0.005, and the mandibular breadth ratio becomes significant at t=2.178, p=0.039.

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Figure 6. Bar graph illustrating relative distribution of CBHI.

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Figure 5. Bar graph illustrating relative distribution of TFI.

The Macedonian and English normal sample skulls can be described using the range descriptions as interpreted by Bass (2005), summarized the bar graphs of figures 5 and 6, above. The most notable divergence between the English and Macedonian samples is in the Total Facial Index, in which the English sample is largely characterized by leptoprosopy, long thin faces, while the Macedonian sample is largely mesoprosopic, medium-faced. The samples also diverge in the Cranial Length-Height Index (CLHI) and Cranial Breadth-Height Index, both suggesting that the English sample were more characterized by “low skulls” than the Macedonian (Bass 2005:71).

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