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Keywords:

  • Neanderthal;
  • wear facets;
  • cusp morphology;
  • maxillary first molar

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS
  5. METHODS
  6. RESULTS
  7. DISCUSSION
  8. CONCLUSIONS
  9. Acknowledgements
  10. LITERATURE CITED

Tooth wear studies in mammals have highlighted the relationship between wear facets (attritional areas produced during occlusion by the contact between opposing teeth) and physical properties of the ingested food. However, little is known about the influence of tooth morphology on the formation of occlusal wear facets. We analyzed the occlusal wear patterns of first maxillary molars (M1s) in Neanderthals, early Homo sapiens, and contemporary modern humans. We applied a virtual method to analyze wear facets on the crown surface of three-dimensional digital models. Absolute and relative wear facet areas are compared with cusp area and cusp height. Although the development of wear facets partially follows the cusp pattern, the results obtained from the between-group comparisons do not reflect the cusp size differences characterizing these groups. In particular, the wear facets developed along the slopes of the most discriminate cusp between Neanderthals and Homo sapiens (hypocone) do not display any significant difference. Moreover, no correlations have been found between cusp size and wear facet areas (with the exception of the modern sample) and between cusp height and wear facet areas. Our results suggest that cusp size is only weakly related to the formation of the occlusal wear facets. Other factors, such as, diet, food processing, environmental abrasiveness, and nondietary habits are probably more important for the development and enlargement of wear facets, corroborating the hypotheses suggested from previous dental wear studies. Anat Rec, 2011. © 2010 Wiley-Liss, Inc.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS
  5. METHODS
  6. RESULTS
  7. DISCUSSION
  8. CONCLUSIONS
  9. Acknowledgements
  10. LITERATURE CITED

The occlusal contacts between crests, cusps, and basins of upper and lower dentition produce attritional wear areas characterized by smooth, polished, and usually well-delineated surfaces called wear facets (Butler,1952; Mills,1955; Every,1972; Kaidonis et al.,1993; Imfeld,1996; Hillson,2003; Kaidonis,2008). Studies on numerous mammals have shown that the type of dental wear and the relative sizes of the wear facets can be related to their diet (Butler,1952,1973; Kay,1977; Janis,1990). In particular, Janis (1990) stated that the development of the occlusal wear facets in mammals is independent from dental morphology. Therefore, in comparing species with similar dental morphology, dietary differences will generate different wear patterns, whereas species with a similar diet but with differences in dental morphology will show similar tooth wear (Janis,1990). No detailed tests of Janis' hypothesis about the lack of correlation between dental morphology and wear facet development have been performed until now. Therefore, the influence of specific dental morphological features on the location, development, and enlargement of wear facets is unknown.

In this study, we quantitatively test if the development of occlusal wear facets is influenced by cusp size by analyzing and comparing tooth wear patterns of species possessing different dental morphology. As dental morphological differences between taxa have also been established by detailed morphometric analysis of cusp area (Wood and Engleman,1988; Bailey,2004), cusp size is used in this study as a metric approach for describing tooth crown morphology. We analyzed and compared wear facet patterns of first maxillary molars (M1s) of Neanderthals, early Homo sapiens, and contemporary modern humans, applying the Occlusal Fingerprint Analysis method (Kullmer et al.,2009) on three-dimensional (3D) polygonal surface models of tooth crowns.

Neanderthal Tooth Morphology

Recent comparative studies have shown that the Neanderthal tooth morphology of first maxillary molars is characterized by distinctive traits with a marked expression and high frequency (Bailey,2002,2004,2006; Gómez-Robles et al.,2007; Quam et al.,2009). The Neanderthal M1 crown commonly consists of four cusps, characterised by a large hypocone that is never reduced or absent, a small metacone, and other additional accessory features (Bailey,2002,2004,2006; Fig. 1A). Carabelli's cusp is frequent and regularly well-developed (Bailey,2006). Distally a fifth cusp, the hypoconule, is common (Bailey,2006). The occlusal outline is characterized by a skewed contour and a rhomboidal shape, resulting from a distolingual enlargement of the hypocone and by the disposition and configuration of internally compressed cusps (Bailey,2002,2004; Gómez-Robles et al.,2007; Quam et al.,2009).

thumbnail image

Figure 1. Photo of Neanderthal (A; Le Moustier 1) and Homo sapiens (B; Inuit FC835) first upper molars in occlusal view (par, paracone; met, metacone; pro, protocone; hyp, hypocone).

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However, this morphology is not unique to Neanderthals and is also found to a lesser extent in early and middle Pleistocene European populations (Gómez-Robles et al.,2007; Quam et al.,2009). In contrast, contemporaneous modern humans typically show a reduced hypocone, a well-developed metacone, and a square occlusal polygon (obtained by connecting the cusp apices of the four major cusps) associated with a square crown outline (Bailey,2002,2004; Gómez-Robles et al.,2007; Quam et al.,2009; Fig. 1B).

Although M1 morphology has been studied thoroughly, very little is known about the occlusal wear pattern in Neanderthal posterior dentition. Occlusal wear was generally used for determining the age-at-death of the Neanderthal specimens from the Krapina cave site in Croatia (Wolpoff,1979). Additionally, an advanced degree of occlusal wear was associated with abrasive food or with an abrasive environment (Trinkaus,1983). In recent years, scientists have focused on the study of occlusal and buccal microwear of Neanderthal posterior dentition using scanning electron microscope images (Lalueza et al.,1996; Pérez-Pérez et al.,2003), confocal microscopy, and scale-sensitive fractal analysis (El Zaatari,2007a,2007b) to reconstruct their diet.

Nevertheless, none of these studies in Neanderthals considered relationship between occlusal wear and cusp size. If the occlusal wear pattern is independent from cusp size, one can expect that the development of wear facets along the slopes of the four maxillary cusps will not be influenced by cusp morphology. Moreover, if this hypothesis will be verified, differences in wear pattern among Neanderthal and early Homo sapiens M1s will be related mostly to dietary differences rather than reflecting dental morphological differences. On the contrary, a strong relation between the development of wear facets and cusp size will indicate that in Late Pleistocene hominins the wear pattern is also affected by the anatomical features of their molars, and the interpretation of any differences should be taken with care.

MATERIALS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS
  5. METHODS
  6. RESULTS
  7. DISCUSSION
  8. CONCLUSIONS
  9. Acknowledgements
  10. LITERATURE CITED

The sample used in this study consists of fossil and modern human M1s. The specimens listed in Table 1 include: Neanderthals (NEA, N = 15), Middle Paleolithic Homo sapiens (MPHS, N = 5), Upper Paleolithic Homo sapiens (UPHS, N = 7), and contemporary modern humans containing the Khoe-san hunter-gatherers (MHS, N = 20). The specimens were chosen based on their degree of occlusal wear. Heavily worn teeth were excluded because occlusal facets tend to fuse with advanced wear, making their precise identification difficult or impossible. For this reason, we have only included slightly-worn molars where facets are identifiable and do not coalesce in the sample. The degree of wear was determined by evaluating the amount of cusp removal and dentin exposure (Smith,1984). To have a homogenous sample and to avoid a marked sample size reduction, only M1s characterized by wear stage 2 (moderate cusp removal, with one or two pinpoint dentin exposures) and stage 3 (full cusp removal and some dentin exposure) were selected.

Table 1. List of fossil and modern human specimens used in this study
SamplesLabelsNSpecimensWeara
  • a

    Wear score system (Smith,1984).

NeanderthalsNEA15Pontnewydd PN4 and PN122
   Krapina 47, 48, 134, 136, 166, 167, and 1712
   Krapina 1643
   Monsempron 2 and 33
   Kůlna 12
   Petit Puy 22
   Le Moustier 12
Middle Paleolithic Homo sapiensMPHS5Qafzeh 5, 9, and 273
   Qafzeh 11 and 152
Upper Paleolithic Homo sapiensUPHS7Mladec 12
   Mladec 23
   Barma Grande 32
   Barma Grande 43
   Sungir 2 and 32
   Pataud 2243
Modern Homo sapiensMHS20Khoe-san3

METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS
  5. METHODS
  6. RESULTS
  7. DISCUSSION
  8. CONCLUSIONS
  9. Acknowledgements
  10. LITERATURE CITED

Occlusal wear pattern analysis was carried out on 3D digital models, which were generated through surface scanning of M1 casts. Dental casts were produced using a special nonreflective plaster (Everest® Rock, KaVo) optimized for light scanning (Fiorenza et al.,2009). We used a white-light scanning system with an xy resolution of 55 μm (smartSCAN 3D, Breuckmann GmbH). The scan-data was collected and aligned by means of the optoCAT software package (v. 2007, Breuckmann GmbH). The digital postprocessing was carried out using PolyWorks® 10 (InnovMetric Software). The digital model of each tooth was imported into the IMEdit module of Polyworks® 10 and the cervical margin was manually delimited using the polyline tool (Ulhaas et al.,2004,2007). A marginal area of 0.2 mm above and below the cervical polyline was defined and a cervical plane was created and inserted by means of the least square, best fit method (Ulhaas et al.,2004,2007; Kullmer et al.,2009) For each wear facet, a closed curve was manually anchored on the digital model following the margin the facet (Ulhaas et al.,2004,2007; Kullmer et al.,2009). Next, the digital triangles included within the facet's perimeter were selected and the areas in mm2 were calculated (Ulhaas et al.,2004,2007; Kullmer et al.,2009).

Wear facets were defined on the occlusal dental surface following the terminology of Maier and Schneck (1981), who identified a maximum of 13 complementary pair facets on hominoid molars (Fig. 2). Additionally, we also identify flat worn areas on the tips of the four main cusps (Gordon, 1984; Janis,1990) and labeled as pro (protocone), par (paracone), met (metacone), and hyp (hypocone).

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Figure 2. Occlusal contacts between the left first maxillary molar and the first and second mandibular molars in the Neanderthal specimen of Le Moustier 1. Wear facets are numbered after Maier and Schneck (1981) and color-coded following their maxillary cusp position: paracone (green), metacone (blue), protocone (red), and hypocone (yellow). The division of homologous wear facets in more parts (as facet 4) is pointed out by the letter a and b. The tip crush areas developed along the tip of the main cusps are identified as pro (protocone), par (paracone), met (metacone), and hyp (hypocone). In this figure, only two tip crush areas are visible on the protocone and hypocone cusp. The arrow indicates the occlusal relationship between the protocone of the upper molar and the central fossa of the lower during maximum intercuspation. B, buccal; L, lingual; M, mesial; D, distal.

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The areas of the facets developed along the slopes of the four major maxillary cusps have been grouped and summed: protocone (facets 5, 5.1, 6, 6.1, 9, 11, 13, and pro), paracone (facets 1, 1.1, 3, and par), metacone (facets 2, 2.1, 4, and met), and hypocone (facets 7, 8, 10, 12, and hyp).

Considering a normal occlusion (Angle Class I), the protocone wear facets of M1 occlude with the central fossa of the lower M1. They are in contact with the buccal slopes of the metaconid and entoconid and with the lingual slopes of the protoconid, hypoconid, and hypoconulid. The paracone wear facets develop for the contacts with the mesiobuccal slope of the hypoconid and with the distobuccal slope of the protoconid of the lower M1. The metacone wear facets occlude with the distobuccal slope of the hypoconid and with the mesiobuccal slope of the hypoconulid of the lower M1. Finally, the development of the hypocone wear facets is because of the contact with the distobuccal slope of the M1 entoconid and with the mesial slopes of the M2.

The total occlusal wear area was calculated as the sum of the absolute area of each occlusal facet. The relative cusp wear facet areas were calculated by dividing the absolute wear area of each cusp by the total occlusal wear area.

Cusp base areas were identified on the polygonal model (oriented in occlusal view) following the major anatomical features that separate the cusps (Wood and Engleman,1988; Bailey,2004; Fig. 3A). Then, the area (in mm2) was calculated projecting the 3D surface of each cusp base on the reference plane (cervical plane) using the IMInspect module of Polyworks® 10 (Fig. 3B). The total crown area was calculated by summing each individual cusp base area. The relative cusp base area was obtained by dividing each absolute cusp base area with the total crown area.

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Figure 3. Left M1 of Le Moustier 1: identification of cusp base areas (A) and their projection on the cervical plane (B). Protocone (par); Paracone (Par); Metacone (met); Hypocone (hyp). The color-code follows Fig. 2.

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Finally, the cusp height was calculated by measuring the perpendicular distance between the maximum tip point and the cervical plane (Fig. 4). An explorative data analysis for each variable [mean and standard deviation (SD)] and for each group was employed to investigate cusp height, absolute and relative cusp wear area differences among hominin groups. As the small sample sizes prevent the assumption of a normal distribution, the intragroup comparison of relative cusp wear areas between molars with different wear stages, as well as the between-group comparisons of absolute and relative cusp areas have been carried out using nonparametric significance tests (Mann-Whitney U test). The P values obtained have been corrected with Bonferroni adjustments.

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Figure 4. Left M1 of Le Moustier 1: calculation of cusp height measuring the perpendicular distance between the highest tip point and the cervical plane (reference plane).

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Finally, the correlation between relative cusp areas and relative wear facet areas and between cusp height and relative wear facet areas has been computed using the Spearman method. The difference in degree of wear may affect the wear facet areas developed along the cusp slopes. Therefore, we computed a statistical comparison of relative cusp wear areas between molars with different wear stages. The statistical analysis has been computed using the R software (R Development Core Team,2008).

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS
  5. METHODS
  6. RESULTS
  7. DISCUSSION
  8. CONCLUSIONS
  9. Acknowledgements
  10. LITERATURE CITED

The results obtained from the comparison within the entire sample of molars characterized by wear stages 2 and 3 show significant differences in the protocone and paracone wear areas (Table 2). However, this result could be due to the fact that most of the NEA specimens studied here show a wear stage 2, while all MHS molars are characterized by a wear stage 3. Consequently, to solve this problem, we carried out one more statistical comparison of relative cusp wear areas considering molars with different wear stages within each group. The reduced sample size of the MPHS sample precludes a statistical analysis (N = 2 for wear stage 2 and N = 3 for wear stage 3), and therefore was not considered. The intragroup comparisons do not show any significant differences in all the groups examined, with the exception of the paracone wear areas within the Neanderthal (NEA) group (Table 2).

Table 2. Between-group comparisons of relative cusp wear areas of molars with different wear stages (2 and 3)
GroupsaHypoconeProtoconeParaconeMetacone
  • Mann-Whitney U test, corrected P values (Bonferroni), and significant P values (<0.05) are highlighted in bold.

  • a

    Group labels follow Table 1.

Entire sample0.441<0.0010.094<0.001
NEA0.8400.1360.0510.101
MPHS    
UPHS0.4000.1140.2290.114
MHS    

The occlusal wear of NEA M1s is characterized by large protocone wear areas, followed by smaller paracone, hypocone, and metacone wear areas (Tables 3 and 4). However, there is large wear pattern variability in the NEA group, especially because of the metacone and hypocone wear areas. Although the protocone wear areas show the largest SD, it continues to be the largest wear area in the NEA group. The most common patterns found are PRO>PAR>HYP>MET (5/15) and PRO>PAR>MET>HYP (4/15). The occlusal wear of the Middle Paleolithic Homo sapiens (MPHS), taking into account the small sample size, returns more homogenous results and follows the pattern PRO>HYP>PAR>MET (4/5).

Table 3. Absolute cusp wear areas in fossil and modern humans
Samplesa (N)Protocone, area (mm2), mean ± SDParacone, area (mm2), mean ± SDMetacone, area (mm2), mean ± SDHypocone, area (mm2), mean ± SD
  • a

    Group labels follow Table 1.

NEA (15)23.4 ± 4.613.8 ± 2.111.7 ± 2.312.9 ± 3.9
MPHS (5)21.7 ± 4.912.3 ± 4.010.6 ± 3.913.9 ± 5.9
UPHS (7)21.8 ± 4.214.5 ± 2.111.8 ± 5.011.5 ± 2.6
MHS (20)17.6 ± 2.513.6 ± 2.214.2 ± 2.811.5 ± 2.7
Table 4. Relative cusp wear areas in fossil and modern humans
Samplesa (N)Protocone, area (%), mean ± SDParacone, area (%), mean ± SDMetacone, area (%), mean ± SDHypocone, area (%), mean ± SD
  • a

    Group labels follow Table 1.

NEA (15)37.5 ± 4.422.4 ± 3.318.9 ± 2.920.4 ± 4.1
MPHS (5)37.2 ± 4.120.6 ± 1.717.5 ± 2.623.0 ± 2.5
UPHS (7)37.1 ± 5.824.6 ± 2.019.1 ± 5.819.3 ± 2.1
MHS (20)31.1 ± 3.627.1 ± 2.524.8 ± 3.320.1 ± 3.8

The hypocone wear facets are well-developed, whereas the metacone wear facets are small. In the UPHS group, the protocone and paracone facets are the largest and most developed wear cusp areas of the entire occlusal crown. Metacone and hypocone wear areas are small and similar in size. Two main wear patterns are found: PRO>PAR>MET>HYP (3/7) and PRO>PAR>HYP>MET (3/7). Finally, the contemporary modern humans (MHS) M1s are characterized by large metacone and paracone wear facets, less pronounced protocone wear areas (if compared with the Pleistocene groups) and by small hypocone facets. The most common wear patterns are PRO>PAR>MET>HYP (7/20) and PRO>MET>PAR>HYP (7/20).

Considering the absolute cusp wear areas, the Neanderthal protocone facets proved to be the largest of the entire sample examined here (Table 3). MPHS show smaller protocone and metacone wear areas and hypocone facets slightly larger than those of NEA. The UPHS sample is characterized by similar protocone wear areas to those of the MPHS, larger paracone facets than those of NEA and MPHS, and by smaller hypocone wear areas than those of NEA and MPHS. Finally, the MHS group shows a smaller protocone wear area than those of Pleistocene hominins, the largest metacone wear area, and the smallest hypocone wear area. However, the absolute wear area differences are not pronounced, as confirmed by the between-group comparisons, which do not show any significant difference, with the exception of the protocone wear facets between NEA and MHS (Table 4).

Taking into account the relative cusp wear areas, the protocone facets are similar in all the Pleistocene hominins and smaller in the MHS sample (Table 5). The paracone wear areas proved to be smaller in the MPHS and NEA groups, whereas they are larger in the UPHS and MHS sample. The largest metacone wear areas are found in the MHS group, followed by the UPHS, NEA, and MPHS sample. Finally, the hypocone wear areas are strongly developed in the MPHS group and smaller in the NEA, UPHS, and MHS sample.

Table 5. Between-group comparisons of absolute cusp wear areas
GroupsaNEAMPHSUPHSMHS
  • Mann-Whitney U test, corrected P values (Bonferroni), significant P values (<0.05) are highlighted in bold.

  • a

    Group labels follow Table 1.

Protocone
 NEA***   
 MPHS1***  
 UPHS11*** 
 MHS<0.0010.2480.111***
Paracone
 NEA***   
 MPHS1***  
 UPHS11*** 
 MHS111***
Metacone
 NEA***   
 MPHS1***  
 UPHS11*** 
 MHS0.0830.761***
Hypocone
 NEA***   
 MPHS1***  
 UPHS11*** 
 MHS111***

The between-group comparisons show significant differences in the protocone relative wear areas between all the Pleistocene groups and the MHS sample (Table 6). Statistically, significant differences are also found in the paracone relative wear areas between MPHS and UPHS and between MPHS and MHS. The metacone relative wear areas display significant differences between MHS and Pleistocene groups. Finally, the between-group comparisons of the relative wear areas developed on the hypocone cusp do not show any level of significance.

Table 6. Between-group comparisons of relative cusp wear areas
GroupsaNEAMPHSUPHSMHS
  • Mann-Whitney U-test, corrected P values (Bonferroni), significant P values (<0.05) are highlighted in bold.

  • a

    Group labels follow Table 1.

Protocone
 NEA***   
 MPHS1***  
 UPHS11*** 
 MHS<0.0010.0070.016***
Paracone
 NEA***   
 MPHS1***  
 UPHS0.6170.03*** 
 MHS0.5860.0141***
Metacone
 NEA***   
 MPHS1***  
 UPHS11*** 
 MHS<0.0010.0030.046***
Hypocone
 NEA***   
 MPHS0.59***  
 UPHS10.18*** 
 MHS10.781***

The cusp height shows a general decrease in molars characterized by a more advanced degree of wear. In wear stage 2 molars, the NEA group is characterized by the highest cusps. In wear stage 3 molars, NEA, UPHS, and MHS display similar cusp height, whereas the MPHS exhibits the highest cusps (Table 7). The relationship between cusp height and relative cusp areas does not show a significant correlation, with the exception of the paracone in the NEA (r = −0.722, P = 0.004) and UPHS sample (r = 0.929, P = 0.007; Table 8).

Table 7. Cusps height in fossil and modern humans
Samplesa (N)Protocone, height (mm), mean ± SDParacone, height (mm), mean ± SDMetacone, height (mm), mean ± SDHypocone, height (mm), mean ± SD
  • a

    Group labels follow Table 1.

Wear stage 2
 NEA (12)6.4 ± 0.76.7 ± 0.77.1 ± 0.86.3 ± 0.7
 MPHS (2)6.6 ± 0.56.1 ± 0.76.1 ± 0.96.1 ± 0.1
 UPHS (4)6.4 ± 0.66.4 ± 1.36.4 ± 1.36.1 ± 1.8
Wear stage 3
 NEA (3)5.1 ± 0.45.7 ± 0.25.8 ± 0.75.0 ± 0.2
 MPHS (3)6.1 ± 1.06.2 ± 0.86.5 ± 0.66.3 ± 0.7
 UPHS (3)5.0 ± 0.65.5 ± 0.36.2 ± 0.45.4 ± 0.7
 MHS (20)5.1 ± 0.75.6 ± 0.65.9 ± 0.75.1 ± 0.7
Table 8. Correlation between cusp height and relative cusp wear areas
GroupsaProtoconeParaconeMetaconeHypocone
  • Spearman method, significant P values (<0.05) are highlighted in bold.

  • a

    Group labels follow Table 1.

NEA0.0590.0040.5670.466
MPHS0.5170.35010.133
UPHS0.2360.0070.3540.556
MHS0.9110.9770.3360.515

The correlation based on the Spearman method between relative base cusp areas and relative cusp wear areas is not significantly different in the Pleistocene hominins with the exception of the NEA protocone (r = 0.768, P = 0.001; Table 9). On the contrary, the MHS sample is characterized by a significant correlation in the protocone (r = 0.722, P < 0.001), metacone (r = 0.544, P = 0.014), and hypocone (r = 0.442, P = 0.052) cusps (Table 9).

Table 9. Correlation between relative cusp base areas and relative cusp wear areas
GroupsaProtoconeParaconeMetaconeHypocone
  • Spearman method, significant P values (<0.05) are highlighted in bold.

  • a

    Group labels follow Table 1.

NEA0.0010.8450.3040.245
MPHS0.2330.450.2330.35
UPHS0.3540.1670.9640.236
MHS<0.0010.6190.0140.052

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS
  5. METHODS
  6. RESULTS
  7. DISCUSSION
  8. CONCLUSIONS
  9. Acknowledgements
  10. LITERATURE CITED

Occlusal wear facets vary in number, size, and shape depending on degree of wear, absolute cusp number, and tooth morphology (Kullmer et al.,2009). However, the intragroup comparisons (Table 2) of relative cusp wear areas did not show any significant difference in molars (with the exception of the Neanderthal paracone) characterized by wear stages 2 and 3. This result suggests that during the first dental wear stages the wear pattern differences, reflected by the relative cusp wear areas, are less pronounced.

The morphology of the lower dentition, together with the presence of malocclusions (dental disorders characterized by a misalignment of teeth), may influence the spatial position and development of the wear facets in the maxillary molars (Fiorenza et al.,2010). However, as the fossil record is often fragmentary and characterized by an incomplete dentition, it is difficult to reach a good sample size for the study of the relationship between upper and lower teeth. Moreover, malocclusions were very rare in hunter-gatherer societies before 19th century, especially in archaic humans (Begg,1954; Hunt,1961; Begg and Kesling,1977; Corruccinni and Pacciani,1989; Proffit and Fields,2000; Evensen and Øgaard,2005). Therefore, we can hypothesize that the influence of malocclusions in the development of the wear facets was negligible in the human fossil sample.

Occlusal wear patterns in NEA, MPHS, and UPHS and in contemporary modern human M1s partially reflect the cusp pattern found in previous studies (Bailey2002,2004; Gómez-Robles et al.,2007; Quam et al.,2009). In the NEA group, the development of cusp wear areas follows a general pattern, where PRO>PAR>HYP>MET. The protocone wear facets are strongly developed, the metacone wear area is reduced, and the hypcone facets are relatively large. Bailey (2002,2004) found the same pattern when analyzing the cusp base areas. However, in our NEA sample, there is high wear pattern variability, especially evident in the metacone and hypocone wear facets.

The MPHS specimens included in this study show a homogenous wear pattern, where PRO>HYP>PAR>MET. Their occlusal crown is characterized by a development of large hypocone wear facets and by a strong reduction of paracone and metacone wear areas. The low variable wear pattern found in MPHS could be because of the smaller sample size, or to the fact that all the specimens (Qafzeh Cave, Israel) most likely belonged to the same population (Tillier,1999). Cusp base area studies of the MPHS M1s have shown a similar pattern to those of NEA, characterized by a strong enlargement of the hypocone and a pronounced reduction of the metacone (Bailey2002,2004; Quam et al.,2009).

The general UPHS cusp wear area pattern is similar to those found in the MPHS group. However, MPHS and UPHS differ because the latter group shows a stronger development of the paracone wear areas and a reduction of the hypocone facets. Similar results were obtained by Bailey (2002,2004), Gómez-Robles et al. (2007), and Quam et al. (2009), which showed the hypocone reduction in the UPHS specimens. However, in the study of Bailey (2002,2004) and Quam et al. (2009), the relative metacone cusp area is larger than that of the hypocone; whereas in our study, the degree of wear facet development along the metacone and hypocone slopes of the UPHS specimens is quite similar.

Finally, in the MHS group the cusp wear facet areas follow the patterns PRO>PAR>MET>HYP and PRO>MET>PAR>HYP. The metacone is particularly developed, whereas protocone and hypocone wear areas are strongly reduced. Morphometric analyses of MHS M1s have brought similar results, showing a pronounced hypocone reduction and an increase of the metacone area (Bailey,2002,2004; Gómez-Robles et al.,2007; Quam et al.,2009). Similar to the NEA group, the MHS sample also shows great variability in cusp wear areas.

However, the between-group comparisons in relative cusp wear areas show rather different results from previous morphometric analyses (Bailey,2002,2004; Gómez-Robles et al.,2007; Quam et al.,2009). Although these studies highlighted that cusp pattern differences among Pleistocene hominins and modern groups can largely be attributed to differences in the relative size of the distal portion of the tooth (Bailey,2004), our analysis shows that differences in the wear facet development can be attributed to the protocone and metacone wear areas. No differences could be found in the hypocone wear areas.

More importantly, the weak relationship between wear facet development and cusp size is corroborated by the absence of correlations found in all the Pleistocene hominins with the exception of the modern sample. These results suggest that wear facet development is not distinctively related to cusp size, agreeing with Janis's work (1990), who stated that differences in dental morphology do not generate differences in occlusal wear patterns if two taxa have similar diets.

Many studies have shown that differences in tooth wear in Homo are related to the physical properties of the ingested food, food preparation techniques, abrasiveness of the environment, and to cultural and nondietary habits (Molnar,1972; Kay,1977; Hinton,1981; Smith,1984; Teaford and Walker,1984; Frayer and Russel,1987; Janis,1990; Lucas,2004; Ungar et al.,2008).

Therefore, the strong correlation found between cusp size and wear patterns in the modern sample, is probably due to the fact that all the modern specimens studied belong to Khoe-san populations, characterized by similar dietary and cultural habits. The absence of major discriminatory factors, such as diet and food preparation methods, leads to similar occlusal wear patterns, which are also reflected through a close relationship with cusp size.

On the contrary, the Pleistocene groups consist of specimens characterized by a large geographical, chronological, ecological, and climatic variation, which also allowed (and necessitated) the exploitation of a greater variety of food sources. These factors result to be more important than dental morphological variations in determining the development of the wear facets.

The absence of correlation (with the exception of the paracone in Neanderthal and UPHS groups) between cusp heights and cusp wear areas indicates that the articulation with the lower molars at these wear stages does not create wear pattern differences. This result may be due to the fact that only M1s in full occlusion were selected for this analysis. Moreover, maxillary first molars exhibit the most stable morphology within the molar series (Scott and Turner,1997). The cusp height-cusp wear area relationship may be stronger in molars characterized by a great cusp reduction. For example, the strong distal cusp reduction, often characterizing second and third maxillary molars, may prevent the occlusal contact with the opposing lower molars. Thus, wear patterns could be strongly influenced by the degree of cusp development, because a full occlusion would be reached only in more advanced wear stages.

CONCLUSIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS
  5. METHODS
  6. RESULTS
  7. DISCUSSION
  8. CONCLUSIONS
  9. Acknowledgements
  10. LITERATURE CITED

The study on the occlusal wear pattern of maxillary first molars in Late Pleistocene and modern humans has shown that the cusp size is only of secondary importance to the development of occlusal wear facets. No wear pattern differences have been found on the distal portion of the tooth, and no correlations have been found between cusp sizes and wear facet areas in the Pleistocene groups. Other factors, such as diet and food preparation methods, are probably more important for the wear pattern formation, as suggested by previous analyses (Butler,1952,1973; Kay,1977; Janis,1990).

However, to better interpret the importance of the ingested food on the formation of tooth wear, this type of study should be extended to other recent hunter-gatherer populations characterized by different subsistence strategies, where detailed information on dietary habits are available.

Finally, a larger sample, including individuals with a complete dentition, could be used to better understand the contact relationship between maxillary and mandibular teeth regarding the dynamics of jaw movements, and their influence on the position and development of the occlusal wear facets.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS
  5. METHODS
  6. RESULTS
  7. DISCUSSION
  8. CONCLUSIONS
  9. Acknowledgements
  10. LITERATURE CITED

The authors thank the following curators and institutions for access to comparative and fossil specimens: Tatiana Baluyeva and Elizavieta Veselovskaya (Institute of Ethnology and Anthropology, Russian Academy of Sciences, Moscow), Angiolo Del Lucchese (Museo Preistorico dei Balzi Rossi, Ventimiglia, Italy), Marta Dočkalová (Moravské Zemské Muzeum, Brno, Czech Republic), Almut Hoffmann (Museum für Vor- und Frühgeschichte, Berlin, Germany), Fabio Parenti (Istituto Italiano di Paleontologia Umana, Rome, Italy), Yoel Rak (University of Tel Aviv, Israel), Chris Stringer and Rob Kruszynski (Natural History Museum, London, UK), National Museum of Wales (Cardiff, Wales), Maria Teschler-Nicola (Naturhistorisches Museum, Vienna, Austria), and Erik Trinkaus (Washington University, Saint Louis, MO) and also thank Christine Hemm for technical assistance and Matt Westwood for copy-editing the manuscript.

LITERATURE CITED

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  2. Abstract
  3. INTRODUCTION
  4. MATERIALS
  5. METHODS
  6. RESULTS
  7. DISCUSSION
  8. CONCLUSIONS
  9. Acknowledgements
  10. LITERATURE CITED
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