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MicroCT Scan in paleobiology: application to the study of dental tissues
Nuclear Instruments and Methods in Physics Research B 213 (2004) 747–750 www.elsevier.com/locate/nimb
MicroCT Scan in paleobiology: application to the study of dental tissues M. Rossi a, F. Casali
a,*
, D. Romani a, L. Bondioli b, R. Macchiarelli c, L. Rook
d
a Department of Physics, University of Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy National Prehistoric Ethnographic ‘‘L. Pigorini’’ Museum, P.le G. Marconi 14, 00144 Rome, Italy Lab. de G eobiol., Biochron. et Pal eont. humaine, Univ. de Poitiers, 40 av. Recteur Pineau, 86022 Poitiers, France d Earth Sciences Department and Museum of Natural History (Section of Geology and Palaeontology), University of Florence, Via G. La Pira 4, 50121 Florence, Italy b
c
Abstract State of the art in paleoanthropological and paleoprimatological research foresees the use of advanced non-destructive investigative approaches. Microcomputed tomography (microCT) is a fundamental tool, since it offers the opportunity to get high quality morphological information with high spatial resolution. We carried out the set-up of an experimental microCT system able to examine paleobiological samples. The equipment can operate on small objects (size up to 3 cm) with a nominal spatial resolution of 30 lm, allowing their 3D volume reconstruction and morphometric analysis. This approach represents a forefront technique in paleobiological studies, successfully employed only in a limited number of advanced research centers. A specific program of microCT analysis has been planned on a sample of human and non-human fossil primate dentitions, in order to assess the specific nature of a number of tooth lesions (e.g. caries versus abrasion). This currently in progress experimental activity represents the first step for the set-up of a research center specifically devoted to the realization of advanced studies in the field of archaeo-paleobiology. 2003 Elsevier B.V. All rights reserved. Keywords: Microcomputed tomography; Non-destructive evaluation (NDE); Charge coupled device; Paleobiology
1. Introduction One relevant developing research field in paleobiology is represented by the inspection/record of specimens by means of non-invasive and nondestructive advanced analytical techniques. In this perspective, microCT potentially represents a key
*
Corresponding author. Tel.: +39-051-2095131; fax: +39051-253274. E-mail address: [email protected] (F. Casali).
tool, since it allows the high spatial resolution (tens of microns) record of inner structures. In addition, microCT data/images can be elaborated for the realization of high quality 3D digital reconstructions and models. Such 3D reconstructions can be used to visualize hidden structures and details, to investigate fine morphological variation, to perform advanced morphometric analyses (including geometric morphometrics). In the frame of an ongoing collaborative research project in paleobiology, we realised some pivotal studies on alterated and pathologic ancient
0168-583X/$ - see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0168-583X(03)01697-5
748
M. Rossi et al. / Nucl. Instr. and Meth. in Phys. Res. B 213 (2004) 747–750
dental tissues by means of a microCT equipment set up at the Department of Physics of the University of Bologna.
2. The microtomographic system The inspection system consists of a 200 kVp, 3 mA, microfocus X-ray tube, a high precision programmable stage and an X-ray detector (Fig. 1). The detector has been assembled with several parts selected to optimize performance and costs. Basically, it consists of a thin Gd2 O2 S:Tb phosphor layer (30 mg/cm2 ) deposited on a 2:1 fiberoptic taper (FOT) optically coupled to a cooled charged coupled device (CCD) camera. The useful detection area is 30 · 15 mm2 with a pixel size of about 30 lm. The system acquires 12 bits digital images (1024 · 512 pixels) in real time. The cone beam geometry with the small focal spot of the X-ray tube (up to 8 lm) allows to magnify small samples increasing the effective spatial resolution [5].
3. Reconstructing the history of dental caries in Primates The currently available record on dental diseases in fossil mammals, including primates, is scanty; nonetheless, differential pathological diagnosis in non-hominid fossil primates may provide interesting information about the diet and lifestyle of these extinct taxa.
Among the various dental lesions/diseases, in this preliminary phase, our study focused on caries. This disease, basically resulting from bacterial acid production in the dental plaque, consists of the progressive destruction of dental tissues – enamel, dentine and cementum – ultimately leading to the formation of a cavity in the crown or root surface. The widely reported epidemiology of dental caries in extant human populations shows a characteristic pattern, where environmental and cultural-related factors, such as food treatment and daily diet (especially quality and amount of sugar intake), play a fundamental role. This pathology is moderately common also among wild great apes [3], where taxon-specific frequency rates vary according to different dietary habits. For instances, gorillas show a very low rate compared to chimpanzees, whose diet includes a greater amount of fruit, and therefore of sugar. Reconstructing the history of this pathology through the conventional investigation of ancient teeth from archaeological and/or paleontological contexts reveals a number of methodological difficulties and intrinsic limits. In most cases, the direct morphological observation of the crown, or even its bidimensional radiographical projection, may leave a significant margin of diagnostic incertitude. This is especially true in the case of incomplete, altered, or broken specimens, that is, in almost the totality of the investigated cases. We used microCT technology in order to tentatively detail the nature of dental lesions on a human tooth of archaeological interest (Case 1) and on the dental crown of a fossil ape (Case 2). This approach allowed high resolution qualitative and quantitative analyses, ultimately leading to differential diagnosis.
4. Case 1
Fig. 1. Scheme of the experimental set-up.
The first case (Fig. 2(A)) represents a human molar (SCR 232) from the Imperial Roman necropolis of Isola Sacra [2]. In occlusal view, the crown surface distincly shows a cavity at the level of the entoconid cusp. The lesion, certainly not accidental (postmortem), nor artificial, is large,
M. Rossi et al. / Nucl. Instr. and Meth. in Phys. Res. B 213 (2004) 747–750
749
Fig. 2. (A) Human molar from the Imperial Roman necropolis of Isola Sacra (spec. SCR 232). (B) SCR 232: the 3D reconstruction in occlusal view. (C) SCR 232: (para)mesio-distal section through the carious cavity.
sub-circular, affecting the occlusal enamel and extending deeply into the underlying dentine. Following microCT scanning, the tooth has been reconstructed in 3D (Fig. 2(B)). The elaboration shown in Fig. 2(C) represents the tridimensional reconstruction of the specimen according to a (para)mesio-distal section; following this segmentation, part of the volume has been virtually removed in order to evidence the location of the cavity and to assess its extension relative to the pulp chamber and to the molar volume, as a whole. The results leave no doubts to a specific diagnosis of caries.
5. Case 2 If we exclude australopithecines and fossil Homo, no systematic investigation has been performed to date on the dental health status of fossil primates. At the best of our knowledge, the carious lesion identified on a lower third molar (M3 ) of the Late Miocene ape Oreopithecus bambolii represents the oldest known occurrence of this disease in Hominoidea. With its typical hominoid postcranial skeleton, a specialized dentition, and an unusual cranial morphology, Oreopithecus is a rather peculiar
Fig. 3. (A) Oreopithecus mandibular portion (IGF 4351) in occlusal view. Arrow indicates the cavity on the M3 occlusal surface; dotted lines delimitate the portion surveyed by microCT. (B) IGF 4351: para-sagittal CT section. Arrow indicates the high density area of the dentine below the cavity. (C) IGF 4351: segmentation of the 3D Oreopithecus reconstruction, with virtual extraction of M3 portion from its alveolus.
750
M. Rossi et al. / Nucl. Instr. and Meth. in Phys. Res. B 213 (2004) 747–750
fossil ape, whose taxonomic status has been (and still partially is) debated since long time [1]. The IGF4 351 specimen, which represents a Oreopithecus right partial mandibular body bearing a portion of the first molar (M1 ), the damaged second molar (M2 ) and the complete M3 (Fig. 3(A)), shows a very unusual feature: a cavity on the occlusal surface of the last molar, located between the protoconid and the hypoconid. This trait, detected by H€ urzeler in his original description of the fossil [4], was tentatively interpreted as a pathological lesion. Evidence from microCT confirms its cariogenic nature. Shape and extension of the lesion are clearly detectable following the microtomographic parasagittal section of the specimen, shown in Fig. 3(B). The shape of the cavity, characterized by a relatively narrow opening fissure in respect of its maximum diameter, is typical of the so-called ‘‘pit caries’’. This kind of carious lesions originates deep in an enamel fissure, or pit, of the occlusal surface. Once the enamel-dentine junction has been reached, the developing lesion spreads towards the dentine roof. Even in an advanced stage of lower cavitation, the caries may not be apparent at the crown surface until the enamel is undermined and collapses [3]. Just below the cavity, a related higher density area, interpreted as an area of sclerotic re-mineralisation, is usually detectable on the dentine. In conclusions, this fossil ape certainly experienced dental caries.
6. Conclusions In order to detail the fine internal (and external) morphology of a number of (osteo)dental remains of archaeological and paleontological interest, we have experienced microCT technology and 3D volume reconstruction (see Fig. 3(C)); this approach represents the only high-quality non-destructive and non-invasive method currently available in paleobiological research.
Despite their apparent similarity, the specimens reported in this study (SCR 232 and IGF 4351) originate from very diverse chronological contexts, and testify very different taphonomic histories. Together, they outline the huge potentialities of microCT applications in paleobiological research, and allow us to underline the following general points for further investigations: 1. according to our experience in human paleobiology and vertebrate paleontology, although the detailed record and reliable morphological interpretation of (osteo)dental remains by means of traditional methods is usually affected/limited by a number of taphonomic factors, the use of microCT technology allows a non-destructive high-resolution access to hidden structures; 2. when systematically applied, the microCT approach may provide quantitatively and qualitatively reliable and comparable sets of data and images characterized by a high degree of reproducibility and replicability, suitable for a variety of 2D and 3D morphological and morphometric analyses, including geometric morphometrics. References [1] D.M. Alba, S. Moya-Sola, M. K€ ohler, L. Rook, in: L. de Bonis, G. Koufos, P. Andrews (Eds.), Hominoid Evolution and Climatic Change in Europe. 2. Phylogeny of the Neogene Hominoid Primates of Eurasia, Cambridge University Press, Cambridge, 2001, p. 284. [2] L. Bondioli, R. Macchiarelli, International Symposium Humans from the Past: Advancement in Research and Technology, Rome, 1997. [3] S. Hillson, Dental Anthropology, Cambridge University Press, Cambridge, 1996. [4] J. H€ urzeler, Schweizerischen Palaeontologischen Abhandlungen 66 (1949) 1. [5] M. Rossi et al., in: U. Bonse (Ed.), Developments in X-Ray Tomography III, Proceedings of SPIE, Vol. 4503, The Society of Photo-Optical Instrumentation Engineers (SPIE), Bellingham, WA, USA, 2002, p. 338.
MicroCT Scan in paleobiology: application to the study of dental tissues M. Rossi a, F. Casali
a,*
, D. Romani a, L. Bondioli b, R. Macchiarelli c, L. Rook
d
a Department of Physics, University of Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy National Prehistoric Ethnographic ‘‘L. Pigorini’’ Museum, P.le G. Marconi 14, 00144 Rome, Italy Lab. de G eobiol., Biochron. et Pal eont. humaine, Univ. de Poitiers, 40 av. Recteur Pineau, 86022 Poitiers, France d Earth Sciences Department and Museum of Natural History (Section of Geology and Palaeontology), University of Florence, Via G. La Pira 4, 50121 Florence, Italy b
c
Abstract State of the art in paleoanthropological and paleoprimatological research foresees the use of advanced non-destructive investigative approaches. Microcomputed tomography (microCT) is a fundamental tool, since it offers the opportunity to get high quality morphological information with high spatial resolution. We carried out the set-up of an experimental microCT system able to examine paleobiological samples. The equipment can operate on small objects (size up to 3 cm) with a nominal spatial resolution of 30 lm, allowing their 3D volume reconstruction and morphometric analysis. This approach represents a forefront technique in paleobiological studies, successfully employed only in a limited number of advanced research centers. A specific program of microCT analysis has been planned on a sample of human and non-human fossil primate dentitions, in order to assess the specific nature of a number of tooth lesions (e.g. caries versus abrasion). This currently in progress experimental activity represents the first step for the set-up of a research center specifically devoted to the realization of advanced studies in the field of archaeo-paleobiology. 2003 Elsevier B.V. All rights reserved. Keywords: Microcomputed tomography; Non-destructive evaluation (NDE); Charge coupled device; Paleobiology
1. Introduction One relevant developing research field in paleobiology is represented by the inspection/record of specimens by means of non-invasive and nondestructive advanced analytical techniques. In this perspective, microCT potentially represents a key
*
Corresponding author. Tel.: +39-051-2095131; fax: +39051-253274. E-mail address: [email protected] (F. Casali).
tool, since it allows the high spatial resolution (tens of microns) record of inner structures. In addition, microCT data/images can be elaborated for the realization of high quality 3D digital reconstructions and models. Such 3D reconstructions can be used to visualize hidden structures and details, to investigate fine morphological variation, to perform advanced morphometric analyses (including geometric morphometrics). In the frame of an ongoing collaborative research project in paleobiology, we realised some pivotal studies on alterated and pathologic ancient
0168-583X/$ - see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0168-583X(03)01697-5
748
M. Rossi et al. / Nucl. Instr. and Meth. in Phys. Res. B 213 (2004) 747–750
dental tissues by means of a microCT equipment set up at the Department of Physics of the University of Bologna.
2. The microtomographic system The inspection system consists of a 200 kVp, 3 mA, microfocus X-ray tube, a high precision programmable stage and an X-ray detector (Fig. 1). The detector has been assembled with several parts selected to optimize performance and costs. Basically, it consists of a thin Gd2 O2 S:Tb phosphor layer (30 mg/cm2 ) deposited on a 2:1 fiberoptic taper (FOT) optically coupled to a cooled charged coupled device (CCD) camera. The useful detection area is 30 · 15 mm2 with a pixel size of about 30 lm. The system acquires 12 bits digital images (1024 · 512 pixels) in real time. The cone beam geometry with the small focal spot of the X-ray tube (up to 8 lm) allows to magnify small samples increasing the effective spatial resolution [5].
3. Reconstructing the history of dental caries in Primates The currently available record on dental diseases in fossil mammals, including primates, is scanty; nonetheless, differential pathological diagnosis in non-hominid fossil primates may provide interesting information about the diet and lifestyle of these extinct taxa.
Among the various dental lesions/diseases, in this preliminary phase, our study focused on caries. This disease, basically resulting from bacterial acid production in the dental plaque, consists of the progressive destruction of dental tissues – enamel, dentine and cementum – ultimately leading to the formation of a cavity in the crown or root surface. The widely reported epidemiology of dental caries in extant human populations shows a characteristic pattern, where environmental and cultural-related factors, such as food treatment and daily diet (especially quality and amount of sugar intake), play a fundamental role. This pathology is moderately common also among wild great apes [3], where taxon-specific frequency rates vary according to different dietary habits. For instances, gorillas show a very low rate compared to chimpanzees, whose diet includes a greater amount of fruit, and therefore of sugar. Reconstructing the history of this pathology through the conventional investigation of ancient teeth from archaeological and/or paleontological contexts reveals a number of methodological difficulties and intrinsic limits. In most cases, the direct morphological observation of the crown, or even its bidimensional radiographical projection, may leave a significant margin of diagnostic incertitude. This is especially true in the case of incomplete, altered, or broken specimens, that is, in almost the totality of the investigated cases. We used microCT technology in order to tentatively detail the nature of dental lesions on a human tooth of archaeological interest (Case 1) and on the dental crown of a fossil ape (Case 2). This approach allowed high resolution qualitative and quantitative analyses, ultimately leading to differential diagnosis.
4. Case 1
Fig. 1. Scheme of the experimental set-up.
The first case (Fig. 2(A)) represents a human molar (SCR 232) from the Imperial Roman necropolis of Isola Sacra [2]. In occlusal view, the crown surface distincly shows a cavity at the level of the entoconid cusp. The lesion, certainly not accidental (postmortem), nor artificial, is large,
M. Rossi et al. / Nucl. Instr. and Meth. in Phys. Res. B 213 (2004) 747–750
749
Fig. 2. (A) Human molar from the Imperial Roman necropolis of Isola Sacra (spec. SCR 232). (B) SCR 232: the 3D reconstruction in occlusal view. (C) SCR 232: (para)mesio-distal section through the carious cavity.
sub-circular, affecting the occlusal enamel and extending deeply into the underlying dentine. Following microCT scanning, the tooth has been reconstructed in 3D (Fig. 2(B)). The elaboration shown in Fig. 2(C) represents the tridimensional reconstruction of the specimen according to a (para)mesio-distal section; following this segmentation, part of the volume has been virtually removed in order to evidence the location of the cavity and to assess its extension relative to the pulp chamber and to the molar volume, as a whole. The results leave no doubts to a specific diagnosis of caries.
5. Case 2 If we exclude australopithecines and fossil Homo, no systematic investigation has been performed to date on the dental health status of fossil primates. At the best of our knowledge, the carious lesion identified on a lower third molar (M3 ) of the Late Miocene ape Oreopithecus bambolii represents the oldest known occurrence of this disease in Hominoidea. With its typical hominoid postcranial skeleton, a specialized dentition, and an unusual cranial morphology, Oreopithecus is a rather peculiar
Fig. 3. (A) Oreopithecus mandibular portion (IGF 4351) in occlusal view. Arrow indicates the cavity on the M3 occlusal surface; dotted lines delimitate the portion surveyed by microCT. (B) IGF 4351: para-sagittal CT section. Arrow indicates the high density area of the dentine below the cavity. (C) IGF 4351: segmentation of the 3D Oreopithecus reconstruction, with virtual extraction of M3 portion from its alveolus.
750
M. Rossi et al. / Nucl. Instr. and Meth. in Phys. Res. B 213 (2004) 747–750
fossil ape, whose taxonomic status has been (and still partially is) debated since long time [1]. The IGF4 351 specimen, which represents a Oreopithecus right partial mandibular body bearing a portion of the first molar (M1 ), the damaged second molar (M2 ) and the complete M3 (Fig. 3(A)), shows a very unusual feature: a cavity on the occlusal surface of the last molar, located between the protoconid and the hypoconid. This trait, detected by H€ urzeler in his original description of the fossil [4], was tentatively interpreted as a pathological lesion. Evidence from microCT confirms its cariogenic nature. Shape and extension of the lesion are clearly detectable following the microtomographic parasagittal section of the specimen, shown in Fig. 3(B). The shape of the cavity, characterized by a relatively narrow opening fissure in respect of its maximum diameter, is typical of the so-called ‘‘pit caries’’. This kind of carious lesions originates deep in an enamel fissure, or pit, of the occlusal surface. Once the enamel-dentine junction has been reached, the developing lesion spreads towards the dentine roof. Even in an advanced stage of lower cavitation, the caries may not be apparent at the crown surface until the enamel is undermined and collapses [3]. Just below the cavity, a related higher density area, interpreted as an area of sclerotic re-mineralisation, is usually detectable on the dentine. In conclusions, this fossil ape certainly experienced dental caries.
6. Conclusions In order to detail the fine internal (and external) morphology of a number of (osteo)dental remains of archaeological and paleontological interest, we have experienced microCT technology and 3D volume reconstruction (see Fig. 3(C)); this approach represents the only high-quality non-destructive and non-invasive method currently available in paleobiological research.
Despite their apparent similarity, the specimens reported in this study (SCR 232 and IGF 4351) originate from very diverse chronological contexts, and testify very different taphonomic histories. Together, they outline the huge potentialities of microCT applications in paleobiological research, and allow us to underline the following general points for further investigations: 1. according to our experience in human paleobiology and vertebrate paleontology, although the detailed record and reliable morphological interpretation of (osteo)dental remains by means of traditional methods is usually affected/limited by a number of taphonomic factors, the use of microCT technology allows a non-destructive high-resolution access to hidden structures; 2. when systematically applied, the microCT approach may provide quantitatively and qualitatively reliable and comparable sets of data and images characterized by a high degree of reproducibility and replicability, suitable for a variety of 2D and 3D morphological and morphometric analyses, including geometric morphometrics. References [1] D.M. Alba, S. Moya-Sola, M. K€ ohler, L. Rook, in: L. de Bonis, G. Koufos, P. Andrews (Eds.), Hominoid Evolution and Climatic Change in Europe. 2. Phylogeny of the Neogene Hominoid Primates of Eurasia, Cambridge University Press, Cambridge, 2001, p. 284. [2] L. Bondioli, R. Macchiarelli, International Symposium Humans from the Past: Advancement in Research and Technology, Rome, 1997. [3] S. Hillson, Dental Anthropology, Cambridge University Press, Cambridge, 1996. [4] J. H€ urzeler, Schweizerischen Palaeontologischen Abhandlungen 66 (1949) 1. [5] M. Rossi et al., in: U. Bonse (Ed.), Developments in X-Ray Tomography III, Proceedings of SPIE, Vol. 4503, The Society of Photo-Optical Instrumentation Engineers (SPIE), Bellingham, WA, USA, 2002, p. 338.