Human Craniofacial Variation and Dental Anomalies: An anthropological investigation into the relationship between human craniometric variation and the expression of orthodontic anomalies

Krecioch, Joseph R

Title: Human Craniofacial Variation and Dental Anomalies: An anthropological investigation into the relationship between human craniometric variation and the expression of orthodontic anomalies

Human Craniofacial Variation and Dental Anomalies: An anthropological investigation into the relationship between human craniometric variation and the expression of orthodontic anomalies

by Joseph R Krecioch (Author)

Medicine - Dentistry

53115

Summary

Dental anomalies of number, shape, and position are frequently analysed in the orthodontic and clinical literature but are rarely discussed in an anthropological or archaeological context. Dental anomalies and occlusal disorders are often hypothesised to be the result of a modern, urbanised lifestyle as a response to reduced masticatory stress and subsequent crowding of the dentition. This study of skulls from Classical to medieaval Macedonia and England examines the relationship between craniofacial variation and the expression of dental anomalies. Standard craniometric measurements were taken to estimate relative sizes of cranial functional complexes and determine whether or not, or to what extent, changes in the shape or size of these variables were associated with the expression of dental anomalies.<br>Statistical analyses determined that the null hypothesis, that there is no relationship between craniometrics and dental anomalies, can be rejected. A number of dental anomalies were found to have a relationship with reduced sizes in cranial and masticatory elements, although dental crowding was not as significant a factor in masticatory complex reduction. A cause and effect relationship cannot be determined but the data presented here suggests that both heredity and environmental causes may be influential in the expression of dental anomalies.

Excerpt

Transpositions ... 58

Rotations and reversals ... 58

Ectopic eruptions and impactions ... 59

Dental Crowding ... 59

Relationships between dental anomalies and craniometrics ... 60

Heritability, population variation and dental anomalies ... 61

Mandibular and dental arch dimensions and the aetiology of dental anomalies ... 68

VI. Conclusion ... 72

REFERENCES ... 74

Appendices ... 84

List of Figures

Figure1. Mildly rotated left mandibular premolars, Hickleton 36. ... 41

Figure 2. Peg-shaped left maxillary M3, Chichester 33. ... 42

Figure 4. Bar graph illustrating relative distribution of CBHI. ... 47

Figure 3. Bar graph illustrating relative distribution of TFI. ... 47

Figures 5, (left), 6 (right). Boxplots showing relative size differences in

mandibular features with and without tooth rotations. ... 48

Figures 7 (left), 8 (right). Graphs showing relative frequencies of rotations

among Total Facial Index categories, English and Macedonian samples. ... 51

Figure 9. Scatterplot of select indices to rotation prevalence in population samples

(normal skulls). Samples with higher rates of rotations cluster among high CI,

and low CBHI and MAI. ... 66

Figure 10. Scatterplot indicating skulls with rotations inclined toward higher

MAX/BCDL indices and medial Facial Breadth (FB1) indices. ... 69

List of Tables

Table 1. Heritability estimates. ... 25

Table 2 Collections summary ... 38

Table 3 List of cranial landmark measurements. ... 39

Table 4 Distribution of anomalies by sex. See text. ... 45

Table 5 Prevalence of Anomalies by Population Sample. ... 45

Table 6 Summary of mean, significant difference of craniometrics with anomalies. 49

Table 7 Means of craniometric variables, any anomaly absent and present.. ... 52

Table 8 Means of craniometric variables with crowding absent or present. . ... 52

Table 9 Means of craniometric variables by population rotation prevalence,

normal skulls only. ... 64

Table 10 Means of craniometric indices by population, normal skulls only. ... 65

Table 11Means of new indices and ratios by population, normal skulls only. ... 65

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 exclusively 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

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, h

, described by the

formula:

(1)

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)

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

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.

Element, module

Estimated

heritability

Source

Vault 0.66

von

Cramon-Taubadel

2011

Dermatocranium 0.62

Chondrocranium 0.61

Nasal 0.57

Face 0.53

Auditory 0.49

Orbit 0.25

Temporal 0.69

von

Cramon-Taubadel

2009

Full cranium

0.64

Sphenoid 0.62

Parietal 0.60

Frontal 0.57

Maxilla 0.56

Occipital 0.54

Zygomatic 0.37

Nasal height (NLH)

0.73

Carson 2006

NLH

0.43

Martínez-Abadías et al 2009

Bimaxillary breadth (ZMB)

0.60

Carson 2006

ZMB

0.07

Martínez-Abadías et al 2009

Cranial length (GOL)

0.36

Carson 2006

GOL

0.31

Martínez-Abadías et al 2009

Occipital chord (OCC)

0.33

Carson 2006

OCC

0.04

Martínez-Abadías et al 2009

Parietal Chord (PAC)

0.31

Carson 2006

PAC

0.06

Martínez-Abadías et al 2009

Bizygomatic breadth (ZYB)

0.26

Carson 2006

ZYB

0.28

Martínez-Abadías et al 2009

Malar length, max (XML)

0.24

Carson 2006

XML

0.20

Martínez-Abadías et al 2009

Cranial Breadth (XCB)

0.23

Carson 2006

XCB

0.36

Martínez-Abadías et al 2009

Biauricular breadth (AUB)

0.40

Martínez-Abadías et al 2009

Foramen Magnum length (FOL)

0.38

Martínez-Abadías et al 2009

Basion-Nasion length (BNL)

0.24

Martínez-Abadías et al 2009

Table 1. Some published heritability estimates of major cranial elements, regions, or measurements

(higher numbTable 1er 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 (Kirzio÷lu 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 2

premolars (Jacob et

al 2006).

Non-syndromic supernumerary teeth have been reported and treated since at

least as early as the 7

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 co0mplete 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 13

and 16

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 16

and 17

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 (4

century BC-4

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.

Collection Total

Individuals

Skulls, Male

Skulls, Female

Total Skulls

English Samples

Blackfriars 192 9

8 17

Box Lane

Hickleton 28 6 6 12

Chichester 354 25 11 36

Subtotal 662

Macedonian Samples

Marvinci 192

15 14 29

Demir Kapija

505

Subtotal 697

Total 1359

131

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.

Measurement Code

Landmarks

Component

Maximum cranial length

GOL

g-op

Vault

Maximum cranial breadth

XCB

eu-eu

Vault

Cranial height

BBH

ba-b

Vault

Facial height

TFH

n-gn

Face

Facial breadth

ZYB

zy-zy

Face

Upper facial height

NPH

n-pr

Face

Upper facial breadth

FMT

fmt-fmt

Face

Maxilloalveolar length

MAXL pr-alv

Palate, external

Maxilloalveolar breadth

MAXB ect-ect

Palate, external

Palatal length

ol-sta

Palate, internal

Palatal breadth

enm-enm

Palate, internal

Bicondylar breadth

BCDL

cdl-cdl

Mandible

Bigonial breadth

BGO

go-go

Mandible

Height of ascending ramus

HAR

go-cdl

Mandible

Min breadth of ascending ramus

MBAR

Mandible

Height of mandible at symphysis HMS

gn-ini

Manidble

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

calipers. 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)

Figure1. Mildly rotated left mandibular premolars,

Hickleton 36.

(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:

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.

· Hypodontia. The congenital absence of each expected tooth was recorded,

and 3

molar agenesis regarded independently as well.

· Transposition. Any interchange of normal tooth positions was recorded, or

any tooth in an unexpected socket.

· 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 1, right.

· Misshapen or peg-shaped teeth, unless supernumerary, were recorded. See

figure 2, below.

· Impactions, ectopic and heterotopic eruptions and crowding were recorded

and analysed along with anomalies.

· Other maxillofacial anomalies, pathological conditions, and infracranial

syndromes with dental involvement were noted.

Congenital Syndromes

Evidence for congenital syndromes and dysplasias were recorded, to be analysed

separately from normal results.

Figure 2. Peg-shaped left maxillary M3, Chichester 33.

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 p0.05 as not significant, p0.05

as significant, and p0.01 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

Female, N=55

Male, N=76

All, N=131

Cases Prevalence Cases Prevalence Cases Prevalence

Any Anomaly other than Crowd Present

54.5%

44.7%

48.9%

Supplemental Teeth

Present

.0%

2.6%

1.5%

Rotation

Present

32.7%

23.7%

27.5%

Reversal

Present

3.6%

.0%

1.5%

Peg, Misshapen

Present

.0%

5.3%

3.1%

Congenitally Absent Teeth

Present

3.6%

2.6%

3.1%

M3 Congenitally Absent

Present

9.1%

9.2%

Ectopic, heterotopic, impaction Present

12.7%

11.8%

12.2%

Crowding

Present

18.2%

27.6%

23.7%

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.

Supplemental

Supernumeraries

Rotations

Reversals

Peg,

Misshapen

Congenitally

Absent Teeth

Congenitally

Absent

Ectopic,

heterotopic,

impaction

Crowding

Cases

Blackfriars,

N=17

.0%

11.8%

.0%

5.9%

.0%

11.8%

5.9%

11.8%

Box Lane,

N=9

11.1%

.0%

11.1%

22.2%

Chichester,

N=36

2.8%

36.1%

.0%

5.6%

2.8%

8.3%

19.4%

Demir

Kapija,

N=28

.0%

21.4%

.0%

10.7%

7.1%

14.3%

Hickleton,

N=12

.0%

33.3%

.0%

8.3%

.0%

16.7%

25.0%

Marvinci,

N=29

.0%

34.5%

6.9%

.0%

3.4%

6.9%

20.7%

44.8%

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 (

=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 (p0.05) 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 (p0.05, 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.

Figure 3. Bar graph illustrating

relative distribution of TFI.

Figure 4. Bar graph illustrating

relative distribution of CBHI.

Details

Pages
Type of Edition: Erstausgabe
Year: 2014
ISBN (eBook): 9783954898299
ISBN (Softcover): 9783954893294
File size: 11.1 MB
Language: English
Publication date: 2014 (November)
Keywords: human craniofacial variation dental anomalies

Author

Joseph R Krecioch (Author)

Human Craniofacial Variation and Dental Anomalies: An anthropological investigation into the relationship between human craniometric variation and the expression of orthodontic anomalies

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Author

Joseph R Krecioch (Author)