J. Anal. (1992) 180, pp. 387-393, with I figure Printed in Great Britain

A comparison of tooth structure in Neanderthals and earlyHomo sapiens sapiens: a radiographic study

URI ZILBERMAN AND PATRICIA SMITH

Department of Anatomy and Embryology, Dental School of Medicine, The Hebrew University-Hadassah Ein Karem,Jerusalem, Israel

(Accepted 30 December 1991)

ABSTRACT

Tooth components of 1st and 2nd erupted permanent molars were measured from standardised radiographsof Homo sapiens sapiens and Homo sapiens neanderthalensis. Enamel height was greater in Homo sapienssapiens but pulp height and width and the height of the enamel to floor of the pulp chamber were greater inHomo sapiens neanderthalensis. Dentine height, crown width and enamel width showed similar results in thetwo groups. Unerupted first molars were measured to analyse the influence of function on tooth componentsand the results obtained were always within the range measured for the erupted teeth. Discriminant analysisbetween groups, using tooth components, showed accuracy of 93% for identification of Homo sapienssapiens and 94% for identification of Homo sapiens neanderthalensis. The results support the hypothesis of adistinct evolutionary line for the Neanderthals.

INTRODUCTION

Teeth are the best preserved part of the skeleton andso play a major role in evolutionary studies. Age hasno direct influence on teeth as it has on other parts ofthe skeleton. Only attrition and dental disease in-fluence the morphology of teeth and the results areeasily recognised. Due to attrition, enamel thickness isreduced, dentine height increases (secondary andtertiary dentine apposition) and pulp size decreases;thus the ratio of enamel height to dentine or pulpheight is changed (Ten Cate, 1985). The dentalphenotype expressed in tooth size and morphologyhas been used to classify phylogenetically the re-lationship of the Neanderthals to Homo sapienssapiens. Morphologically, the Neanderthal teeth showcharacteristic features such as taurodontism, large sizeof lingual tubercles and Carabelli's trait (Gorjanovic-Kramberger, 1906; Keith, 1925; Kallay, 1963; Smith,1989).Tooth components (enamel, dentine and pulp size)

are determined genetically. The 'freezing' of thedentinoenamel junction early in life and the rate andduration of enamel apposition (Ten Cate, 1985)

influence both tooth morphology and size. Growth ofenamel is promoted by factors on the X and Ychromosomes (Alvesalo et al. 1985; Varrela et al.1988). The effect may occur through the regulation ofamelogenesis, with the X chromosome more effectivein increasing metric enamel growth and the Ychromosome in promoting general dental growth(Alvesalo et al. 1985, 1987). Interspecies differencesin enamel and pulp thickness were shown betweenAustralopithecus africanus and Australopithecusrobustus permanent molars (Zilberman et al. 1991,1992). The results suggested that tooth size isinfluenced both by the outline of the tooth at thedentinoenamel junction and by the thickness ofenamel.

Thickness of enamel in modern humans wasmeasured by Shillinburg & Grace (1973). They usedground sections that intersect the cusp tips bucco-lingually in upper molars and mesiodistally in lowermolars. The same technique was used to determinedifferences in enamel thickness in primates (Molnar &Gantt, 1977); differences in average enamel thicknessbetween primates and Sivapithecus (Martin, 1985) anddifferences in enamel structure between modern

Correspondence to Dr Uri Zilberman, Laboratory of Physical Anthropology, Department of Anatomy and Embryology, Dental School ofMedicine, The Hebrew University-Hadassah Ein Karem, P.O. Box 1172, Jerusalem 91010, Israel.

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humans and early hominids (Grine & Martin, 1988).The invasive technique used in these studies is notapplicable to the rare early hominid specimens.However, some measurements of enamel thickness inParanthropus (Robinson, 1956) and Australopithecushave been made using naturally fragmented teeth(Beynon & Wood, 1986). The 3rd method used formeasuring enamel thickness is radiography of theteeth (Sperber, 1985; Zilberman et al. 1991).Ground sections of teeth have also been used to

measure dentine height (Shillinburg & Grace, 1973)and dentine apposition rates (Molnar et al. 1981). Thepulp chambers of early hominid teeth have beendescribed and measured from radiographic images byKallay (1963), Blumberg et al. (1971), Sperber (1986),Zilberman et al. (1991, 1992), and the radiographicimage of the pulp ofmodern human primary teeth hasbeen compared with the anatomy of the pulp horns(Puddhikarant & Rapp, 1983).The present study, using a radiographic technique,

was designed to determine the significance of differ-ences in tooth components of mandibular permanentmolar teeth between Neanderthals and Homo sapienssapiens and to compare the influence of function onthickness of tooth components.

MATERIALS AND METHODS

This study was based on 31 mandibles of Homosapiens sapiens and 15 mandibles from Neanderthals.From the 2 sides of the mandibles a total of 90mandibular 1st and 2nd molars were examined (Table1). All mandibles were radiographed by the sameperson. The power and voltage were fixed at 10 mAand 65 kV, the only variable being the exposure time.The focus-film distance was 23 cm. The radiographswere taken by applying the film parallel to the majoraxes of the teeth. The X-rays were directed at rightangles to an imaginary plane bisecting the vertical andmesiodistal axes of the teeth and the plane of theradiographic plate - the parallel film technique (Gron1960; Wood et al. 1988). The amount of radiationexposure was consistent with obtaining the sharpestphotographic image possible.

In order to determine the reliability of the radio-graphic method, 10 radiographs of the same specimenwere taken at different angles. It was found thatdeviations of more than 5° in the mesiodistal planeproduced overlapping of adjacent teeth on theradiographic image. Deviation of more than 5° in thevertical plane caused marked separation of the buccaland lingual cusps. Accordingly, only radiographswithout overlapping of adjacent teeth and with full

overlapping of buccal and lingual cusps were used. Toensure lack of bias in taking the measurements, allradiographs were coded so that their attribution wasunknown to the individual at the time of measure-ment.

Seven measurements of tooth components weretaken on each tooth using a digital calliper on a lighttable (see Fig.) by the same person. Enamel height (1),dentine height (2), pulp height (3), and enamel to floor

Table 1. Number ofpermanent mandibular molars measured

Tooth no.

Left MI Left M2 Right MI Right M2

Homo sapiens 22 13 20 11sapiensHomo sapiens 10 5 7 2neanderthalensisSpecimens studied. Early Homo sapiens: Isturits 1950-5, 1950-6,1950-7; Lachaud 5; Saint Germain la Riviere 1979-8 B-3, B-4,B-5; Solutre 1956-49; Fontechevade 1957-53; Le Roc de Sers75113; Le Placard 68098; Le Placard 4, 80628; Le Placard61397; Laugerie Basse 1,2; Les Roches 53143; Roc de Cave;La Pique; le Marin A III; Parpallo; Bruniquel Lafaye 24;Miesslingtal 22034; Bruniquel les Forges 537; Djebel Irhoud 3;Abri Pataud 1; Les Rois; La Genierre 3; Grotte des Enfants 6;Haua Fteah 1; Qafzeh 2,4. N. Neanderthals: Gibraltar;Ehringsdorf; Chateauneuf 2; La Chaise 14, 15; Roc de Marsal;Malarnaud; Le Petit Puymoyen; La Quina H 9; KrapinaB,C,D,E; Vindija 76/232; Montgaudier.

Fig. Measurements taken on each tooth. 1, Enamel height (EH);2, dentine height (DH); 3, pulp height (PH); 1+2+3, enamel tofloor of pulp chamber (CH); 4, pulp width (PW); 5, enamel width(EW); 6, crown width (CW) mesiodistal length.

Components ofpermanent mandibular molars

of pulp chamber (1 + 2 + 3), were measured parallel tothe long axis of the tooth, mesial to the central fossa,on the same line. Maximum enamel width (5) wasmeasured perpendicular to the long axis of the toothat the widest mesial enamel width and pulp width wasmeasured at the maximal mesiodistal width per-pendicular to the long axis of the tooth. Crown width(6) (mesiodistal length) was measured at the level ofmaximum convexity of the mesial and distal surfacesand at right angles to the long axis of the tooth.The range of variation found between measure-

ments taken on different accepted radiographs of thesame specimen was 2-5% and averaged 3.2%. Alldata were transferred to the computer and the 2subsamples compared using statistical analyses takenfrom the SPSS program (Nie et al. 1975).

RESULTS

The number of molars measured in the 2 taxonomicgroups studied are shown in Table 1. Since in mostmandibles only molars of one side were present, allhomologous permanent molars were grouped togetherin order to enlarge the sample for statistical purposes.Case analysis and tooth analysis (homologous teethgrouped together) gave similar results statistically. Allteeth were compared using Student's 2-tailed t test(Tables 2, 3). The P value used for statisticalsignificance was determined at 0.01.

Table 2 shows the results for erupted first man-

Table 2.molars

dibular molars. Pulp height and enamel to floor ofpulp chamber distance were larger in the Neanderthalsbut enamel height was greater in Homo sapiens sapiensand the differences between the 2 species werestatistically significant. Pulp width was greater in theNeanderthals, but the differences were not statisticallysignificant. Enamel width, dentine height and crownwidth showed similar values for both groups.The results for erupted second mandibular molars

are summarised in Table 3. All values, except fordentine height, showed the same trend as in the firstmolars. Pulp height, pulp width, enamel to floor ofpulp chamber distance, and crown width were largerfor the Neanderthal teeth and the differences werestatistically significant. Enamel height was greater inHomo sapiens sapiens teeth but the differences werenot statistically significant and enamel width anddentine height showed similar results for both groups.

Correlations between measurements were examinedusing Pearson's correlation coefficient (Table 4). Theresults showed no correlation between enamel height,dentine height and pulp height. The main correlationsfound were between enamel height and enamel width,pulp height and crown height, enamel width andcrown width, and pulp width and crown width. Therewas a negative but low correlation between enamelheight and dentine height.

Ratios of tooth components were calculated. Themost significant differences between species werefound using the ratio of enamel height to pulp height(Table 5). This ratio was 2 to 4 times greater inmandibular permanent molars of Homo sapiens

Descriptive statistics of erupted mandibular Ist

Variable Group n X (mm) S.D. P value

EH HSS 41 1.67 0.47 0.036HSN 16 1.43 0.34

EW HSS 40 1.25 0.26 0.568HSN 16 1.21 0.27

DH HSS 41 3.27 0.63 0.382HSN 16 3.09 0.63

PH HSS 37 1.24 0.78 0.0008HSN 11 3.42 1.54

PW HSS 38 4.25 0.56 0.304HSN 11 4.47 0.56

CH HSS 37 6.39 1.32 0.004HSN 11 8.30 1.71

CW HSS 40 11.67 0.78 0.595HSN 16 11.80 0.83

EH, enamel height; EW, enamel width; DH, dentine height; PH,pulp height; PW, pulp width; CH, enamel to floor of pulp chamber;CW, crown width; HSS, Homo sapiens sapiens; HSN, Homo sapiensneanderthalensis.

Table 3.molars

Descriptive statistics of erupted mandibular 2nd

Variable Group n X (mm) S.D. P value

EH HSS 23 2.00 0.41 0.122HSN 7 1.72 0.36

EW HSS 23 1.31 0.24 0.562HSN 7 1.27 0.15

DH HSS 23 3.10 0.51 0.319HSN 7 3.36 0.59

PH HSS 22 1.82 0.68 0.003HSN 6 4.26 1.21

PW HSS 23 4.12 0.74 0.025HSN 7 4.65 0.41

CH HSS 22 7.27 1.09 0.011HSN 6 9.78 1.62

CW HSS 23 11.41 0.54 0.012HSN 7 12.50 0.82

Abbreviations as in Table 2.

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Table 4. Values for Pearson's correlation coefficient

First permanent mandibular molars Second permanent mandibular molars

EW DH PH PW CH CW EW DH PH PW CH CW

Homo sapiens sapiensEH 0.4031* -0.2199 0.2047 0.0797 0.3867 0.0719 0.4818* -0.1704 -0.0062 -0.0927 0.2785 0.2142EW -0.1297 0.0988 0.0743 0.3582 0.3626* 0.1093 0.1408 0.1330 0.4516 0.3676DH -0.1807 0.0450 0.3803 0.4850 -0.1061 0.1120 0.3779 0.0068PH 0.0192 0.6853* 0.0161 0.0341 0.7753* 0.0836PW 0.0519 0.4910* 0.1452 0.5617*CH 0.4199* 0.2106Homo sapiens neanderthalensisEH 0.5718* -0.1469 0.3983 -0.3945 0.5631 0.1616 0.3345 -0.1620 0.6961 -0.6496 0.5838 -0.2579EW 0.1798 0.2679 0.0320 0.4164 0.6580* 0.7743 0.7698 0.2945 0.8408 0.6569DH 0.1192 0.1714 0.4184 0.4020 0.4176 0.6066 0.6040 0.8582PH 0.1544 0.9188* 0.1437 -0.2672 0.9735* 0.1438PW 0.1215 0.5207 -0.0938 0.8131CH 0.3587 0.3622

Abbreviations as in Table 2.* P<0.01.

Table 5. Ratio ofenamel height (EH) to pulp height (PH) forerupted mandibular permanent molars

Tooth group

Left Ml Right Ml Left M2

HSS HSN HSS HSN HSS HSN

n 20 6 14 4 15 5Mean 1.98 0.50 1.67 0.50 1.15 0.45

For all teeth P < 0.001.HSS, Homo sapiens sapiens; HSN, Homo sapiens neanderthalensis.

sapiens than in the Neanderthals. The ratios for rightM2 were not given due to the small number ofNeanderthal teeth. The ratio of enamel width tocrown width shows less striking differences but doesdemonstrate that differences in tooth size in the 2species reflect differences in the morphology of thepulp.

Tables 6 and 7 deal with the question as to howfunction and attrition influence the height and widthof tooth components. Unerupted first mandibularmolars were measured for both groups and the resultscompared with those of erupted first mandibularmolars. As expected, function caused decrease inenamel height, enamel width and crown width in bothspecies. For the other components only teeth of Homosapiens sapiens were available for measurements.Function caused decrease in pulp height, pulp widthand enamel to floor of pulp chamber, and increase in

Table 6. Descriptive statistics of the influence offunction onpermanent first mandibular molars ofHomo sapiens sapiens

Variable Status n X (mm) S.D. Range

EH Erupted 40 1.67 0.46 0.42-2.80Unerupted 4 2.08 0.44 1.46-2.48

EW Erupted 40 1.25 0.26 0.60-1.82Unerupted 5 1.72 0.21 1.37-1.93

DH Erupted 41 3.27 0.63 1.88-4.84Unerupted 4 2.94 0.46 2.47-3.54

PH Erupted 37 1.24 0.78 0.25-3.27Unerupted 1 2.46

PW Erupted 38 4.25 0.56 2.82-5.39Unerupted 1 4.33

CH Erupted 37 6.39 1.32 3.37-9.52Unerupted 1 8.23

CW Erupted 40 11.67 0.78 10.28-14.78Unerupted 5 11.96 0.78 10.95-12.67

Abbreviations as in Table 2.

dentine height. The differences were not statisticallysignificant and the results obtained for the uneruptedteeth were always within the range measured for theerupted teeth. The results for the single uneruptedNeanderthal tooth showed the same pattern ofdifferences as for the erupted teeth.

Discriminant analysis of variance was performedusing several combinations of variables. The bestresults were obtained using enamel height and width,pulp height and width, and dentine height, using thetaxonomic categories given in Table 1. For all 1st and

Components ofpermanent mandibular molars

Table 7. Descriptive statistics of the influence offunction onpermanent Ist mandibular molars ofHomo sapiens neander-thalensis

Variable Status n X (mm) Range

EH Erupted 16 1.43 0.86-1.97Not erupted 1 1.84

EW Erupted 16 1.21 0.70-1.58Not erupted 1 1.49

CW Erupted 16 11.80 10.66-13.24Not erupted 1 12.30

Abbreviations as in Table 2.

2nd molars of Homo sapiens sapiens, 93 % weregrouped correctly (52 out of 56 teeth) and 94% ofHomo sapiens neanderthalensis molars were groupedcorrectly (16 out of 17 teeth).The misclassified teeth of Homo sapiens sapiens

were right MI and M2 of Qafzeh 2 with 66 and 95 %probability of belonging to Neanderthals, right Ml ofQafzeh 4 with 69% probability of belonging toNeanderthals, and left MI of Jebel Irhoud with 62%probability of belonging to Neanderthals. The onlymisclassified Homo sapiens neanderthalensis tooth wasright Ml of Vindija 76/232 with 96% probability ofbelonging to Homo sapiens sapiens.

DISCUSSION

Skeletal and morphological differences reported be-tween the Neanderthals and Homo sapiens sapiensindicate that the Neanderthals are a side branch in thehominid evolutionary sequence (Smith & Arensburg,1977; Stringer et al. 1984; Stringer & Andrews, 1988;Protsch, 1989; Smith, 1989; Stringer, 1989). Themajor distinctive metric features of Neanderthal teethare the large buccolingual diameters of the incisors,the ratio of 2nd molar to 1st molar root length, andtaurodontism. These are plesiomorphic traits. How-ever, the marked accentuation of certain features suchas lingual tubercles and taurodontism appears to becharacteristic of the Neanderthal permanent dentition(Smith, 1989). The basis of taurodontism appears tobe a delay in fusion of the interradicular processes(Keith, 1913). Kallay (1963) described the taurodontpulps of the Neanderthals as shown in radiographsand Blumberg et al. (1971) measured them in abiometric study. In comparing the radiographic imageof the pulp with its anatomy it was shown that theoutlines of the lingual horns were contained within thebuccal pulpal images (Puddhikarant & Rapp, 1983),

but that the overall radiographic image of the pulp issimilar to its 3-dimensional anatomy (Barker et al.1969, 1974).This study has shown that there are marked

differences between Neanderthals and Homo sapienssapiens in the height and width of the pulp chamberand in enamel height. The assumption that the thinnerenamel is not due to attrition is based on the methodsand results of this study: the measurements of enamelheight were taken 1 mm mesial to the central fossawhere attrition has minimal impact (Fig. 1) and valuesfor tooth components of unerupted teeth fell withinthe range of variation of the erupted teeth (Tables 6,7). Finally, Pearson's correlation coefficients showedno statistically significant correlation between enamelheight and dentine height or pulp height (Table 4),and the inverse ratios of enamel height to pulp height(Table 5) showed that the differences between specieswere not only due to attrition. The pulp chamber ofNeanderthals showed the expected taurodontism. Thethinner enamel found in them may be explained bygenetic or developmental factors. It may be the resultof slower enamel formation or earlier cessation ofameloblast activity. The teeth of Neanderthals de-veloped faster (Dean, 1985) and erupted earlier thanteeth of Homo sapiens sapiens (Legoux, 1965; Deanet al. 1986). This need for early eruption may haveprovided the trigger to stop enamel formation.The use of tooth components for discriminating

between Homo sapiens sapiens and Neanderthalsshowed promising results. All of the misclassifiedteeth are from specimens whose attribution is stillquestionable. Almost 93 % of all mandibular molarsof Homo sapiens sapiens were correctly grouped. Theincorrectly classified cases were Qafzeh 2 and 4,determined by Trinkaus (1984) as an 'early ana-tomically modern human sample' and by Arensburg(1991), as 'Neanderthaloid', and Jebel Irhoud de-scribed by Brauer (1984) as 'Neandertaloid Homosapiens'. Of the Neanderthal mandibular molars allexcept one were correctly classified. The only in-correctly classified case was Vindija 76/232 which'apparently represents a more gracile variant of theNeanderthals, one which is more similar to ana-tomically modern humans' (Brauer, 1984) and wasclassified as Homo sapiens sapiens by F. H. Smith(1984), Stringer et al. (1984) and Stringer (1989).The discriminant analysis using various tooth

component measurements may help in classifyingsingle tooth or mandibular fragments containingteeth. The characteristic morphological traits of theNeanderthal dentition (Patte, 1959; Smith & Arens-

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burg, 1977; Smith & Tillier, 1989), together with theanalysis of tooth components, suggest that there aremajor differences in dental development betweenNeanderthals and Homo sapiens sapiens. The differ-ences found in this study support the hypothesis thatthe Neanderthals are an evolutionary side branch(Trinkaus, 1983; Stringer et al. 1984; F. H. Smith,1984; P. Smith, 1989: Stringer, 1989).

ACKNOWLEDGEMENTS

We would like to thank Professor Mark Skinner formaking the radiographs available to us for study.

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