Exploring the biomechanics of taurodontismStefano Benazzi,1,2 Huynh N. Nguyen,2 Ottmar Kullmer3 and Jean-Jacques Hublin2

1Department of Cultural Heritage, University of Bologna, Ravenna, Italy2Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany3Department of Palaeoanthropology and Messel Research, Senckenberg Research Institute, Frankfurt am Main, Germany

Abstract

Taurodontism (i.e. enlarged pulp chamber with concomitant apical displacement of the root bi/trifurcation) is

considered a dental anomaly with relatively low incidence in contemporary societies, but it represents a typical

trait frequently found in Neandertal teeth. Four hypotheses can be envisioned to explain the high frequency in

Neandertals: adaptation to a specific occlusal loading regime (biomechanical advantage), adaptation to a high

attrition diet, pleiotropic or genetic drift effects. In this contribution we used finite element analysis (FEA) and

advanced loading concepts based on macrowear information to evaluate whether taurodontism supplies some

dental biomechanical advantages. Loads were applied to the digital model of the lower right first molar (RM1) of

the Neandertal specimen Le Moustier 1, as well as to the digital models of both a shortened and a hyper-

taurodontic version of Le Moustier RM1. Moreover, we simulated a scenario where an object is held between

teeth and pulled in different directions to investigate whether taurodontism might be useful for para-masticatory

activities. Our results do not show any meaningful difference among all the simulations, pointing out that

taurodontism does not improve the functional biomechanics of the tooth and does not favour para-masticatory

pulling activities. Therefore, taurodontism should be considered either an adaptation to a high attrition diet or

most likely the result of pleiotropic or genetic drift effects. Finally, our results have important implications for

modern dentistry during endodontic treatments, as we observed that filling the pulp chamber with dentine-like

material increases tooth stiffness, and ultimately tensile stresses in the crown, thus favouring tooth failure.

Key words: biomechanics; finite element analysis (FEA); Homo neanderthalensis; taurodontism; teeth.

Introduction

Neandertal teeth are peculiar for the high frequency of

specific dental traits, such as large, shovel-shaped incisors,

premolars with complex occlusal morphology, lower pre-

molars with asymmetrical occlusal outline, upper molars

(usually M1) with expanded hypocone, lower molars with

anterior fovea distally bordered by a mid-trigonid crest,

and molars (both uppers and lowers) with enlarged pulp

chambers or taurodont (‘bull-toothed’) roots (Bailey, 2002,

2004, 2006; Kupczik & Hublin, 2010; Benazzi et al. 2011a).

With regard to the last feature, Gorjanovi�c-Kramberger

(1907, 1908) was the first to observe in the Neandertal

Krapina fossil sample that molars (and, to a lesser extent,

premolars) show apically positioned root bifurcation result-

ing in an enlargement of the body (or stem) of the root at

the expense of the root branches. Due to the similarity of

this prismatic root with the condition seen in the teeth of

ungulates, Keith (1913) introduced the term ‘taurodon-

tism’, and subsequently Shaw JCM (1928) Taurodont teeth

in South African races. J Anat 62, 476-498. Classified taur-

odont teeth according to the relative displacement of the

floor of the pulp chamber into hypo-, meso- and hyper-

taurodont forms.

Taurodontism is an anatomical developmental anomaly

seen in permanent and primary teeth, caused by the failure

or delay of Hertwig’s epithelial sheath diaphragm to invagi-

nate at the proper horizontal level (Hamner et al. 1964;

Wright, 2007). Even though the specific molecular signals

that induce the invagination of the epithelial sheath are still

unknown, it has been noted that this process influences

root length (Kovacs, 1971): fast narrowing of the epithelial

sheath produces short and tapered roots, whereas delay or

failure of the invagination produces long roots (or even

pyramidal roots), as often found in Neandertal molars (e.g.

Lebel & Trinkaus, 2002; Macchiarelli et al. 2008; Walker

et al. 2008; Dazbrowski et al. 2013).

Kupczik & Hublin (2010) provided a comprehensive mor-

phometric analysis of this feature comparing European

Neandertals with Late Pleistocene humans from Northwest

Correspondence

Stefano Benazzi, Department of Cultural Heritage, University of

Bologna, Via degli Ariani 1, 48121 Ravenna, Italy.

T: + 39 0544936745; E: stefano.benazzi@unibo.it

Accepted for publication 26 October 2014

Article published online 18 November 2014

© 2014 Anatomical Society

J. Anat. (2015) 226, pp180--188 doi: 10.1111/joa.12260

Journal of Anatomy

Africa (Aterian) and recent Homo sapiens, confirming the

high frequency of taurodontism in Neandertal mandibular

molars and pointing out the larger M1 and M2 root surface

areas in Neandertals than in recent modern humans. Owing

to the link between masticatory function and root surface

area (Spencer, 2003; Kupczik & Dean, 2008) their results sug-

gest that Neandertal molars were subjected to elevated

occlusal forces exercised to comminute hard food items.

Therefore, taurodontism might be a masticatory function-

ally related feature (i.e. an adaptive biomechanical advan-

tage) useful to withstand a specific occlusal loading regime.

Indeed, it has been suggested that the Neandertal cranio-

facial morphology (e.g. marked mid-facial prognathism,

posteriorly positioned zygomatic root) is an adaptation to

resist strong bite forces, mainly applied to the anterior

teeth (e.g. Hylander, 1977; Rak, 1986; Trinkaus, 1987; Smith

& Paquette, 1989; Spencer & Demes, 1993; Wang et al.

2010). However, Ant�on (1994) showed that bite force pro-

duction in Neandertals was smaller than in modern humans

(for both anterior and posterior teeth). Likewise, O’Connor

et al. (2005) pointed out that Neandertal’s bite force was

not exceptionally large when considering cranial size (even

less efficient than many modern humans), a result later sup-

ported by Clement et al. (2012), who suggested that Nean-

dertals were similar to other Late Pleistocene hominins at

least with regard to the anterior dental loadings.

In this contribution we aim to evaluate whether taur-

odontism confers biomechanical advantages in Neandertals.

We used finite element analysis (FEA) and advanced loading

concepts based on macrowear information (Kullmer et al.

2009; Benazzi et al. 2011b, 2012, 2013a,b, 2014) to load the

lower right first molar (RM1) of Le Moustier 1. The analysis

was carried out on the digital volumetric model of the origi-

nal specimen and on the digital models of a shortened and

a hyper-taurodontic version of Le Moustier RM1 to empha-

size the differences (in displacements and stress distribu-

tion), if any, between the original and two extreme

manipulated root shapes. Moreover, we investigated

whether taurodontism might be useful for intensive use of

the molar as a tool (i.e. para-masticatory activities; Fiorenza

& Kullmer, 2013), simulating a scenario where an object is

held between teeth and pulled in different directions.

Materials and methods

We obtained permission from the Museum f€ur Vor- und

Fr€uhgeschichte, Staatliche Museen zu Berlin (Germany) to micro-CT

scan the Neandertal specimen Le Moustier 1. Le Moustier 1 was

selected because of the almost complete upper and lower dentition

and because the molars are only slightly worn, possessing a well-

developed wear facet pattern. Micro-CT scanning was carried out

with a BIR ACTIS high-resolution CT scanner using the following

scan parameters: 130 kV, 100 lA, 0.25 mm brass, and 5000 views

per rotation. Volume data were reconstructed using isometric vox-

els of 66.8 lm for the mandible and 30.6 lm for the maxilla.

The size of the digital models was reduced by cropping the

micro-CT image stack mesially and distally to the socket of the RM1

(for the mandible) and RP4-RM1 (for the maxilla). Segmentation of

the RM1 dental and supporting tissues (enamel, dentine, pulp, alve-

olar and cortical bone), as well as RP4-RM1 dental tissues was carried

out in AVIZO 7 (Visualization Sciences Group Inc.). Periodontal liga-

ment (PDL) for the RM1 was modelled with an interface of 0.2 mm

between the root surface and the alveolar bone, an average value

among those found in the scientific literature (e.g. Hohmann et al.

2011; Xia et al. 2013). As recent in vitro studies suggest that the

enamel-dentine junction (EDJ) plays an important role in accommo-

dating mechanical stresses (Zaytsev & Panfilov, 2014), the EDJ was

modelled as 100-lm-thick layer between enamel and dentine (Mar-

shall et al. 2001).

The final refinement of the digital model (hereafter called RM1-

original) was carried out in GEOMAGIC STUDIO 2012 (Geomagic, Inc.)

(Fig. 1a). In the same software the pulp of RM1-original was digi-

tally modified to simulate a reduced (hereafter called RM1-reduced;

Fig. 1 Dental tissues and supporting

structures for the lower right first molar Le

Moustier 1 (RM1-original), as well as for two

further versions where the pulp chamber of

the RM1 was both reduced, to simulate the

Homo sapiens condition (RM1-reduced), and

increased, to simulate a hyper-taurodontic

root (RM1-hyper). EDJ, enamel-dentine

junction; PDL, periodontal ligament.

© 2014 Anatomical Society

Biomechanics of taurodontism, S. Benazzi et al. 181

Fig. 1b) and a hyper-taurodont (hereafter called RM1-hyper; Fig. 1c)

pulp chamber. In both cases, the position and morphology of the

pulp apices and pulp roof were preserved, and just the bifurcation

was moved upward (for RM1-reduced) and downward (for RM1-

hyper) while constraining its relative position with regard the the

pulp floor. As taurodontism is a continuous trait (in term of expres-

sion), we have selected two representative conditions that might

account for a large range of variation in Neandertal and H. sapiens

pulp shape. In detail, we considered data about root stem volume

(i.e. the volume of the root between the cervical plane and the

plane at bifurcation) published by Kupczik & Hublin (2010) for

Neandertals (417.11 � 145.70 mm3) and H. sapiens (237.90 �58.52 mm3) to guide our simulations. Starting from a root stem vol-

ume of 327.74 mm3 (RM1-original; pulp volume = 87.42 mm3,

which is close to the Neandertal mean, 79.9 � 34.47 mm3,

computed by Kupczik & Hublin, 2010), the volume obtained

for RM1-reduced was 269.45 mm3 (within the range of recent

H. sapiens variability; pulp volume = 72.06 mm3), whereas the vol-

ume obtained for RM1-hyper was 512.41 mm3 (within the upper

range of Neandertal variability; pulp volume = 118.09 mm3).

As suggested in previous contributions (e.g. Benazzi et al. 2011b,

2013a,b, 2014), a preliminary step for FEA requires the identification

of contact areas between the RM1 and the antagonistic teeth dur-

ing a two-body interaction, i.e. tooth–tooth contact, which might

be more damaging to the tooth crown than food–tooth contacts,

because more localized stresses increase (Lucas, 2004). The dental

surface model of the RM1 and RP4-RM1 were imported into OCCLUSAL

FINGERPRINT ANALYSER (OFA) software (Fig. 2a). Thanks to collision detec-

tion, deflection and break-free algorithms, the OFA software allows

one model to be moved against the other, selecting automatically

the colliding triangles of the triangulated crown surface model

(Benazzi et al. 2011b, 2012, 2014; Kullmer et al. 2013). The contact

areas identified during maximum intercuspation were selected for

FEA, thus giving information about the position where occlusal

loads should be applied (red areas in Fig. 2b). For loading direction,

perpendicular loads to the contact areas were applied because we

assumed that during maximum intercuspation contact, compressive

forces act between complementary wear facet pairs (Hattori et al.

2009; Benazzi et al. 2011b). As in the digital versions of Le Moustier

1 RM1 (namely, RM1-original, RM1-reduced and RM1-hyper) the

occlusal surface was not modified, all simulations were character-

ized by the same loading conditions (and boundary constraints; see

below).

The surface models were imported into HYPERWORKS Software

(Altair Engineering, Inc.), where volumetric meshes (for enamel,

dentine, EDJ, pulp, PDL, cortical and alveolar bone) were created

using 10-node tetrahedral elements (Fig. 2c; Supporting Informa-

tion Table S1). Information for material properties (elastic modulus

– E, and the Poisson’s ratio) was collected from the literature

(Table 1). As the E-modulus of EDJ is not constant but is a mono-

tonic decrease from the enamel side of the EDJ to the dentine

(Marshall et al. 2001), an average value between enamel and den-

tine was computed. All the biological materials represented in the

models were considered homogeneous, linearly elastic and isotro-

pic. Although this is an evident simplification for enamel (owing to

the highly anisotropic stiffness characteristics of the enamel), it has

been suggested that dentine can be modelled as an isotropic hard

tissue (Kinney et al. 1999), and that the mechanical properties of

dentine depend strongly on the shape of the specimen under inves-

tigation (Zaytsev et al. 2012). As we aim to explore the pattern of

stress distribution in the root (which is basically made of dentine),

and because in all simulations we used the same material parame-

ters, the same boundary conditions (see below) and the same mor-

phology for enamel and EDJ, the results will ultimately be driven by

the different shapes of the root.

For each version of the Le Moustier RM1 we also evaluated

whether filling the pulp chamber with dentine affects the pattern

of stress distribution in the tooth (hereafter called RM1-original-F,

RM1-reduced-F and RM1-hyper-F). This scenario reflects not only the

physiological deposition of secondary dentine in the pulp chamber

observed during individual life, but also the normal practice in end-

odontic treatment of root canal filling of taurodontic teeth (e.g.

Bharti et al. 2009; Marques-da-Silva et al. 2010).

Boundary constraints were applied to the medial and distal cut

surfaces of the mandible section. The medial nodes were restrained

only in linguo-buccal translation, whereas the distal nodes were

restrained both in mesio-distal and supero-inferior translation

(Benazzi et al. 2012). A uniform pressure of 150 N was distributed

on the RM1 occlusal surface according to the proportion of the

occlusal contact areas detected in the OFA software. We applied

a

b

c

Fig. 2 (a) Collision detection for Le Moustier

1 RM1 with the antagonists RP4-RM1 in the

OCCLUSAL FINGERPRINT ANALYSER software (OFA)

during maximum intercuspation contact. (b)

The RP4-RM1 are transparent to show the

collision (red spots) in the occlusal surface of

the RM1. (c) The FE mesh of RM1-original

consisting of 939 380 10-node tetrahedral

elements. B, buccal; D, distal; L, lingual;

M, mesial;PDL, periodontal ligament.

© 2014 Anatomical Society

Biomechanics of taurodontism, S. Benazzi et al.182

150 N because it is an average force among the loading conditions

found in the literature for modern human (Cheng et al. 2010; Fu

et al. 2010). Even though this value is uncertain, we note that our

goal was to detect patterns of stress distribution in the tooth (which

is not affected by the loading value because at each material point

of the model the stress is linearly proportional to the force applied;

i.e. stress and displacement can be scaled according to load factor),

rather than to predict realistic loads that cause, e.g. fractures in the

root.

Moreover, for each version of Le Moustier RM1 (RM1-original,

RM1-reduced and RM1-hyper) we simulated a scenario wherein an

object, having elastic modulus similar to rubber (E = 0.05 GPa) and

Poisson’s ratio = 0.3, is embedded on the occlusal surface of the

RM1. The embedded material is much softer than the enamel and

dentine so that it does not increase the stiffness of the entire tooth

(Poisson’s ratio value has no influence). A resultant force of 150 N

was applied perpendicular to the object surface (i.e. parallel to the

z-axis), reflecting a scenario that mimics soft tissue processing

behaviour, e.g. food in between teeth during occlusion (load case 1

– LC1; Fig. 3a). To investigate whether taurodontism might be use-

ful for para-masticatory activities, further simulations were carried

out pulling the embedded object either buccally (i.e. towards the

cheek) or mesially (i.e. towards the anterior dentition). Specifically,

loads were applied either parallel to the x-axis (load case 2 – LC2;

Fig. 3b) or parallel to the y-axis (load case 3 – LC3; Fig. 3c) with a

resultant force of 30 N computed as the product between the

perpendicular loading (150 N) and the coefficient of friction of 0.2,

a value found for wet conditions (Li & Zhou, 2002).

For the six versions of Le Moustier RM1 (hence including the

models with filled pulp chamber) we evaluated the displacement

of the tooth and the pattern of maximum principal stresses. Max-

imum principal stresses are presented graphically using colour

maps, with red areas showing highest tensile stresses and

blue areas showing the lowest value (negative values suggest

compression).

Results for the embedding object were qualitatively and quanti-

tatively compared according to the first maximum principal stresses

criterion only.

Due to the small sample size, no statistical test was used to assess

the significance of the results. However, to facilitate the comparison

of the patterns of stress distribution (for maximum principal stres-

ses), we set the range limit of the colour maps at �6 to 6 MPa.

Results

The ultimate displacements of the six digital models of Le

Moustier RM1 are low and very similar to each other when

loaded during a maximum intercuspation contact situation

(Table 2). The largest displacement is found on the x-axis

(bucco-lingual direction), probably due to the contact areas

on the lingual cusps (which are higher than the buccal

ones), which concur to create a resultant occlusal force

slightly lingually directed. We observe a slight decrease of

displacement values when the pulp chamber is filled with

Table 1 Elastic properties of isotropic materials.

Material E* (GPa) Poisson’s ratio References

Enamel 84.1 0.3 Magne (2007)

Dentine 18.6 0.31 Ko et al. (1992)

EDJ 51.35 0.3 Average between enamel and dentine

Pulp 0.002 0.45 Rubin et al. (1983)

PDL 0.0689 0.45 Holmes et al. (1996)

Alveolar bone 11.5 0.3 Dejak et al. (2007)

Cortical bone 13.7 0.3 Ko et al. (1992)

EDJ, enamel-dentine junction; PDL, periodontal ligament.

*Elastic modulus.

Fig. 3 An object was embedded on the

occlusal surface of the RM1 and then a force

was applied perpendicular to the object

surface (load case 1 – LC1), parallel to the x-

axis (i.e. buccally; load case 2 – LC2) and

parallel to the y-axis (i.e. mesially; load case 3

– LC3).

© 2014 Anatomical Society

Biomechanics of taurodontism, S. Benazzi et al. 183

dentine material, suggesting that a filled pulp chamber

increases tooth stiffness.

Similarly, the distributions of maximum principal stress

for RM1-original, RM1-reduced and RM1-hyper are very simi-

lar to each other (Fig. 4a). Tensile stresses are observed in

the grooves of the occlusal surface, mainly in the lingual

groove between the metaconid and entoconid, whereas

the buccal half experiences compressive stresses. The root is

mainly under compression, and the only difference

observed among the three simulations involves a slight

reduction of tensile stresses in the root bifurcation of RM1-

hyper. It is worthwhile noting that modelling the EDJ as

100-lm-thick layers between enamel and dentine decreases

tensile stresses in the crown (but not the general pattern of

stress distribution) as compared with simulations that do

not include the EDJ (Supporting Information Fig. S1).

The pattern of stress distribution is also similar among the

models with the pulp filled with dentine (Fig. 4b). In the

three simulations (RM1-original-F, RM1-reduced-F and RM1-

hyper-F), tensile stresses are concentrated in the grooves of

the lingual aspect of the occlusal surface, constrained

between the mid-trigonid crest and the posterior fovea.

Again, tensile stresses in the root bifurcation slightly

decrease in specimen RM1-hyper-F. Noteworthy, Fig. 4 also

shows that when the pulp chamber is filled with dentine

the magnitude of tensile stresses increases in the enamel

(up to ~25%; Supporting Information Fig. S2), indicating

that a stiffer root negatively affects the crown. As in this

simulation we applied only 150 N on the occlusal surface,

according to P�erez-Gonz�alez et al. (2011) the failure crite-

rion for brittle material, the increased tensile stresses do not

reach the level of failure, but this might happen if the

occlusal load is augmented.

Finally, a similar pattern of stress distribution was also

obtained for RM1-original, RM1-reduced and RM1-hyper

when an object is embedded on the occlusal surface of the

RM1 and loaded separately along the z-axis (LC1), x-axis

(LC2) and y-axis (LC3) (Fig. 5). For LC1, all models show

lower tensile stresses than during maximum intercuspation

contact, presumably because the load was less localized and

more uniformly distributed on the whole occlusal surface.

For LC2, all models experience tensile stresses on the lingual

half of the root. For LC3, the stresses are concentrated on

the occlusal surface and on the distal half of the root,

where RM1-hyper shows lower magnitude than either RM1-

original or RM1-reduced.

Discussion and Conclusions

In modern societies, taurodontism has been reported to

account for less than about 5% of the human population,

even though a wide discrepancy in the prevalence of the

trait has been observed due to ethnic variations and differ-

ent criteria used to interpret this trait (Jafarzadeh et al.

2008). Conversely, we observe a high frequency of taur-

odontism in Neandertal teeth, at least European Neander-

tals (Kupczik & Hublin, 2010), suggesting that the trait

might confer biomechanical advantages for withstanding

and distributing the occlusal loadings produced during the

power stroke.

Using a digital approach that allows the same specimen

to be compared (Le Moustier RM1) with its original mor-

phology and different root morphologies, our results sug-

gest that taurodontism does not improve dental

biomechanics. In all simulations (including those with the

pulp chamber filled with dentine), there are no meaningful

differences in displacement and stress distribution in RM1-

reduced and RM1-hyper digital models. The difference in

tensile stress magnitude observed in the bifurcation is so

low and localized that it is unlikely to require evolution

towards taurodontism. Similarly, taurodontism does not

seem to favour para-masticatory activities, as all simulations

show the same patterns and almost the same magnitude of

maximum principal stresses (except for a decrease in tensile

stresses in RM1-hyper relative to load case 3 – LC3, i.e. pres-

sure in the Y direction).

Excluding the biomechanical hypothesis, we are left with

three potential explanations for the high frequency of taur-

odontism in Neandertals: either a selective advantage to

prolong tooth longevity in a high attrition diet, and ulti-

mately to preserve the health of the periodontium (Coon,

1962; Blumberg et al. 1971), or pleiotropic or genetic drift

effects, as it was observed that mutation of some genes

might affect root formation (e.g. Steele-Perkins et al. 2003).

Table 2 Ultimate displacement in x-, y- and z-axes and the magnitude (mm) of the Le Moustier RM1 digital versions under a uniform pressure of

150 N.

Specimen ux uy uz Magnitude

RM1-original �8.401E-03 3.035E-03 �7.056E-03 1.138E-02

RM1-original-F* �8.307E-03 3.004E-03 �6.989E-03 1.126E-02

RM1-reduced �8.656E-03 3.058E-03 �7.199E-03 1.167E-02

RM1-reduced-F* �8.556E-03 3.031E-03 �7.133E-03 1.154E-02

RM1-hyper �8.644E-03 2.933E-03 �7.161E-03 1.160E-02

RM1-hyper-F* �8.557E-03 2.886E-03 �7.087E-03 1.148E-02

*The pulp chamber is filled with material with dentine properties.

© 2014 Anatomical Society

Biomechanics of taurodontism, S. Benazzi et al.184

The former hypothesis (which might take place either by

filling in the pulp chamber with secondary dentin or delay-

ing the exposure of the bifurcation during the physiological

eruption of worn teeth, which is required to maintain the

occlusion between antagonists; Coon, 1962; Blumberg et al.

1971) is attractive, but it is at odd when considering that

Late Pleistocene H. sapiens, including modern humans from

pre-industrialized societies, were characterized by heavy

tooth wear, a condition that changed little until very

recently (Molnar, 1972; Kaifu, 2000; Kaifu et al. 2003;

Kaidonis, 2008; Benazzi et al. 2013a). Despite that, modern

humans do not show the high frequency of taurodontism

typical of Neandertals (Kupczik & Hublin, 2010). Rather,

nowadays taurodontism is recognized as a clinical challenge

during endodontic treatment, owing to the variation in the

size and shape of the pulp chamber, the complexity of the

root canal system, the apically positioned canal orifices,

requiring special handling during cavity preparation, root

canal filling as well as tooth extraction (e.g. Jafarzadeh

et al. 2008; Bharti et al. 2009; Manjunatha & Kovvuru,

2010; Marques-da-Silva et al. 2010; Bronoosh et al. 2012;

Simsek et al. 2013; Radwan & Kim, 2014). Therefore, even

though we cannot rule out the selective advantage of taur-

odontism for coping with a high attrition environment, it is

reasonable to assume that the high frequency of this trait

in Neandertals is the result of either the side effect of

genetic conditions related to other phenotypic expressions

under positive selection (pleiotropy), or (mechanically neu-

tral) genetic drift effects that may have started with

Homo heidelbergensis groups or even earlier. Indeed, rela-

tively high percentages of hypotaurodontism were found in

the Sima de los Huesos hominins (Martin�on-Torres et al.

2012). The Pleistocene, particularly the late Middle Pleisto-

cene and Late Pleistocene, were characterized by climati-

cally unstable glacial periods with episodes of icecap and

permafrost expansion, which ultimately modified the geog-

raphy of Europe (van Andel & Tzedakis, 1996; Fletcher et al.

2010; Sanchez Go~ni & Harrison, 2010). During these cold

and dry conditions, Neandertal population sizes severely

decreased (probably as a result of high local mortality rates)

a

b

Fig. 4 The maximum principal stress (MPa)

distribution for specimen RM1-original, RM1-

reduced (i.e. the bifurcation was moved

upward) and RM1-hyper (i.e. the bifurcation

was moved downward) with either unfilled

(a) or filled (b) pulp chamber (i.e. RM1-

original-F, RM1-reduced-F and RM1-hyper-F).

Blue spots in the occlusal surface

(compressive stress) represent the contact

areas with the antagonistic teeth during

maximum intercuspation (where the load was

applied), whereas red spots represent tensile

stresses. B, buccal; D, distal; L, lingual;

M, mesial.

© 2014 Anatomical Society

Biomechanics of taurodontism, S. Benazzi et al. 185

and environmental constraints reduced movements of pop-

ulations between Europe, Central Asia and the Near East

(Hublin, 2009; Hublin & Roebroeks, 2009). Periodic isola-

tions, demographic collapses, and the retraction into war-

mer refugia might have resulted in genetic bottlenecks and

drift effects, thus explaining the reduced morphological

variability observed in European Neandertals (Weaver et al.

2007) and ultimately the high frequency of taurodontism in

this group.

Clinical relevance

A final remark, with important implications for modern

dentistry, concerns the results we obtained when filling the

pulp chamber with dentine. This digital simulation, which

mirrors general protocols followed by dentists during end-

odontic treatments when filling root canals with various

sealing materials (e.g. amalgam, composite resins, mineral

trioxide aggregate, calcium phosphate cement), shows that

a filled pulp increases tooth stiffness (Table 2), and ulti-

mately tensile stresses in the crown (Fig. 4b), augmenting

the risk of tooth fracture. Indeed, several dentists have

emphasized the risk of tooth fracture following endodontic

treatments (e.g. Batur et al. 2013; Taha et al. 2014; Tennert

et al. 2014), pointing out that intact natural teeth show

superior fracture strength than endodontically treated

teeth (Pradeep et al. 2013). Furthermore, we observed that

the EDJ might play an important role to decrease tensile

stresses in the crown, as also argued by other scholars (e.g.

Zaslansky et al. 2006; Shimizu & Macho, 2007; Zaytsev &

Panfilov, 2014). Therefore, we suggest preserving tooth

structure wherever possible (ideally, using more elastic

restorative materials that decrease tooth stiffness) to

reduce tensile stresses in the crown and the resulting risk of

tooth failure.

Acknowledgements

We are grateful to the Museum f€ur Vor- und Fr€uhgeschichte in

Berlin and in particular to Almut Hoffmann for providing access to

the original specimen and allowing the acquisition of lCT data of

Le Moustier 1 skull fragments and mandible. The data are stored in

the digital database of the Max-Planck Institute for Evolutionary

Anthropology in Leipzig. This is publication no. 73 of the DFG

Research Unit 771 ‘Function and performance enhancement in the

mammalian dentition – phylogenetic and ontogenetic impact on

the masticatory apparatus’.

Authors’ contributions

S.B.: study concepts and design, and microCT data segmen-

tation. S.B., H.N.N.: 3D volumetric mesh and finite element

analysis (FEA). S.B., O.K.: occlusal fingerprint analysis (OFA).

S.B., H.N.N., O.K., J.J.H.: data interpretation and writing of

manuscript.

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Supporting Information

Additional Supporting Information may be found in the online

version of this article:

Fig. S1 The maximum principal stress (MPa) distribution for spec-

imen RM1-original, RM1-reduced (i.e. the bifurcation was moved

upward) and RM1-hyper (i.e. the bifurcation was moved down-

ward) without modelling the enamel-dentine junction (EDJ).

Fig. S2 Difference of the maximum principal stress (%) between

the crowns of the models with non-filled/filled pulp chambers

based on 12 homologous nodes selected on the occlusal

grooves.

Table S1 Numbers of nodes and tetrahedral elements for each

specimen.

© 2014 Anatomical Society

Biomechanics of taurodontism, S. Benazzi et al.188