Journal of Archaeological Science 36 (2009) 1637–1646
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Developmental defects and postmortem changes in archaeological pig teeth from Fais Island, Micronesia Horst Kierdorf a, *, Uwe Kierdorf a, Carsten Witzel a, Michiko Intoh b, Keith Dobney c a
Department of Biology, University of Hildesheim, Marienburger Platz 22, 31141 Hildesheim, Germany National Museum of Ethnology, 10 Senri Expo-Park, Suita, Osaka 565-8511, Japan c Department of Archaeology, University of Durham, South Road, Durham DH1 3LE, United Kingdom b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 November 2008 Received in revised form 23 March 2009 Accepted 24 March 2009
The study investigated developmental defects of the dental hard tissues and postmortem changes in archaeological pig molars from Fais Island, Micronesia. The developmental defects of enamel were indicative of a disturbance of the secretory stage (accentuation of the incremental pattern, occurrence of Wilson bands and of hypoplastic defects) and the maturation stage of amelogenesis (hypomineralisation). Presence of coronal cementum in an M3 indicated a partial premature breakdown of the reduced enamel epithelium or a partial demise of the enamel organ earlier during tooth development. Developmental defects of dentine presented as accentuated Andresen lines and areas of interglobular dentine. The pattern of developmental defects in the studied molars and the fact that deciduous premolars of the pigs from Fais did not exhibit developmental defects on macroscopic inspection are consistent with the hypothesis that the tooth defects were caused by periods of severe nutritional stress occurring after weaning. Postmortem changes caused by microbial infiltration were recorded in dentine and cementum. A presumed case of soft tissue preservation in the form of presence of odontoblast processes was observed in an M1. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: Coronal cementum Domestic pig Enamel hypoplasia Interglobular dentine Nutritional stress Taphonomy
1. Introduction Around 3000–3500 BP an Austronesian-speaking population dispersed from island Southeast-Asia into Remote Oceania, bringing with them a range of horticultural crops and a set of domesticated animals (pigs, dogs, and chickens) as well as the commensal Pacific rat, Rattus exulans (Hurles et al., 2003; Intoh and Shigehara, 2004; Matissoo-Smith and Robins, 2004). As colonization proceeded eastwards, the domesticated animals were also transported to newly settled islands as a vital part of the subsistence economy of the island populations. The distribution of domesticated animals was, however, not uniform in Remote Oceania. By the time of European contact, chickens were widespread, while dogs and pigs were distributed mainly in Melanesia and Polynesia. In Micronesia, originally no pigs were reported except for the small island of Palau (Intoh, 1986; Intoh and Shigehara, 2004; Masse et al., 2006). The first archaeological excavation on Fais island (Central Caroline islands, Federated States of Micronesia) was conducted in
* Corresponding author. Tel.: þ49 5121 883913; fax: þ49 5121 883911. E-mail address:
[email protected] (H. Kierdorf). 0305-4403/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2009.03.028
1991 (Intoh, 1993). Fais is a small raised coral island (15–20 m a.s.l.) with a land area of about 2.8 km2, located at latitude 9 460 N and longitude 140 310 E (Fosberg and Evans, 1969). The excavation results indicate that Fais has been inhabited by humans since about 40–400 AD. Interestingly, the discovered faunal remains comprised the whole set of Austronesian domesticated animals, including 47 pieces of domestic pig bone and teeth (Intoh and Shigehara, 2004). As could be judged from the presence of many isolated epiphyses of the metacarpals and metatarsals, the high frequency (c. 43%) of deciduous teeth among the excavated pig teeth and the only slight wear of the recovered permanent teeth, most of the pig remains were from young individuals. While the seven recovered deciduous premolars (one dp2, one dp3, five dp4s) did not exhibit enamel abnormalities, a high frequency of enamel hypoplasia was recorded for the excavated permanent premolars and molars (Intoh and Shigehara, 2004). Thus, five of the eight recovered pig molars and one of the two recovered complete third permanent premolars exhibited hypoplastic enamel defects. Intoh and Shigehara (2004) hypothesized that the high frequency of enamel hypoplasia in the permanent teeth may indicate that the pigs on the small, resourcelimited island of Fais had suffered from severe nutritional stress. It has previously been documented that the frequency of enamel hypoplasia in pig dentitions can be linked to different husbandry
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practices and that among the multiple aetiologies that can cause enamel hypoplasia, nutritional stress may play an important role (Ervynck and Dobney, 1999; Dobney and Ervynck, 2000; Dobney et al., 2004; Witzel et al., 2006). Studies in domestic pigs and wild boar also suggested that histological analysis of developmental defects of enamel enables an assessment of the duration and intensity of stress episodes of different nature that affected enamel formation (Kierdorf et al., 2004, 2005; Witzel et al., 2006). After tooth eruption, dental enamel is incapable of further growth or repair. Thus, only stress events occurring during the period of amelogenesis leave their traces in the enamel of a particular tooth. Hypoplastic defects of enamel indicate stress events affecting the secretory stage of amelogenesis that precedes the maturation stage in which the enamel achieves its final high mineral content. Contrary to enamel, dentine continues to be formed also after tooth eruption, and therefore also stress events occurring in later life can leave their traces in the dentine. The aims of the present study were to (1) analyze the developmental defects in the dental hard tissues of archaeological pig molars from Fais island, (2) reconstruct the timing and intensity of the stress episodes affecting dental hard tissue formation in the pigs, and thereby to test the hypotheses that nutritional stress may be the cause underlying the formation of these defects, and (3) undertake a differential diagnosis of developmental defects and postmortem changes in the teeth. 2. Materials and methods Three of the five excavated pig molars from Fais exhibiting enamel hypoplasia were available for study. The analyzed teeth were a right maxillary first molar (FS 91-1518), a right mandibular second molar (FS 91-1526), and a right mandibular third molar (FS 91-1529; find numbers from Intoh and Shigehara, 2004). Two of the teeth (M2 and M3) originated from the same excavation square, while the M1 was excavated in a different square. However, each of the teeth was found in a different stratigraphic layer, so that it is very unlikely that they had belonged to the same individual. Calibrated radiocarbon dates (obtained on charcoal samples) for the stratigraphic layers in which the teeth were found are 1073–1285 AD for the M1, 895–1205 AD for the M2 and 553–777 AD for the M3 (Intoh and Shigehara, 2004). Mesiodistal (m-d) and buccolingual/buccopalatal (b-l/b-p) crown diameters of the teeth (in millimetres) were 15.3 (m-d) and 12.9 (b-p) for the M1, 21.7 (m-d) and 15.9 (b-l) for the M2, and 30.4 (m-d) and 17.2 (b-l) for the M3 (Intoh and Shigehara, 2004). Applying the aging system for wild boar teeth by Carter and Magnell (2007), which is based on crown and root formation stages, the age at death of the pigs from which the M2 and M3 originated, was estimated at 12–13 months and 12–16 months, respectively. In both teeth, root formation was incomplete. The M3 was unerupted and its crown therefore unworn. In contrast, root formation in the M1 was complete, and the tooth crown showed slight to moderate wear. In Sus scrofa, completion of M1 root formation occurs at 5–7 months of age (Carter and Magnell, 2007). Since the M1 in question was already worn to some extent, age at death of the individual from which it originated was probably similar to that of the other two pigs from which a molar was studied. The teeth were first inspected macroscopically, using a magnifying lens if necessary, and photographed (Canon EOS 300D), and then processed for microscopic study. For this, they were embedded in epoxy resin (Biodur E12/E1, Biodur Products, Heidelberg) and transversely sectioned axiobuccopalatally (M1) or axiobuccolingually (M2, M3) through the highest point of the mesial lobe using a rotary saw with a water-cooled diamond blade (Woko 50, Conrad Apparatebau, Clausthal-Zellerfeld). For scanning electron microscopy, the cut surface of one of the resulting blocks from each
specimen was polished using a motorized rotary polisher (LaboPol5, Struers, Copenhagen) and pads of decreasing grit size (grades 500, 1000, 1200). The samples were then further polished using 9, 3, and 1 mm particle size diamond suspensions, and the final polishing was done with a colloidal silica suspension (OP-S suspension, Struers). Subsequently the samples were cleaned and air dried. Scanning electron microscopy (SEM) of the samples was performed using both backscattered electron (BSE) and secondary electron (SE) imaging modes. For BSE imaging of the polished surfaces, uncoated specimens were transferred to an FEI Quanta 600 FEG scanning electron microscope (equipped with a solid-state backscattered electron detector) that was operated in a low vacuum mode at an accelerating voltage of 20 kV. Prior to SE imaging, the specimens were etched for 3 s with 34% (v/v) phosphoric acid. They were then rinsed with distilled water, dried, mounted on aluminium stubs, sputter-coated with gold or goldpalladium, and viewed in a Hitachi S 520 scanning electron microscope operated at an accelerating voltage of 10 kV. For light microscopy, the cut surface of the other half of each sectioned tooth was polished using silicon carbide paper (grades 360, 600, 1200, 2400) and a solid compound polish (Menzerna, ¨ tigheim), and mounted with the polished side down to a glass slide. O The mounted specimen was then sectioned to a thickness of approximately 300 mm with the rotary saw, ground and polished to a final thickness of approximately 50 mm, and cover-slipped. The ground sections were viewed and photographed in ordinary transmitted light using an Axioskop 2 Plus microscope (Zeiss) equipped with a Canon PowerShot G2 digital camera. Acquired images were processed using the software package Photoshop 7.0 (Adobe). 3. Results 3.1. Macroscopic findings On macroscopic inspection, all teeth showed severe abnormalities (Fig. 1). The tooth crown of the M1 exhibited a brownish colouration of the enamel and numerous enamel defects of either developmental or posteruptive origin (Fig. 1a and b). Defects of developmental origin presented as several pits in mid-coronal enamel and a prominent horizontal row of larger hypoplastic defects that encircled the base of the tooth crown. The latter were oval to round in contour and, especially on the buccal crown side, often confluent with each other (Fig. 1a and b). In extended regions of the crown (most prominent buccally), larger areas of surface enamel were missing, the areas of reduced enamel thickness being clearly demarcated from the adjacent full thickness enamel (Fig. 1b). These defects were diagnosed to be of posteruptive origin, being caused by the flaking-off of larger areas of (mechanically compromised) outer enamel during mastication. The fact that the margins of the posteruptive defects were smoothed due to wear indicated their intravital origin. The enamel of the M2 also showed a brownish colouration (Fig. 1c and d). Pit-type hypoplastic defects were scattered over the crown surface, occurring most frequently in the upper crown half. A plane-type hypoplastic defect was observed on both crown sides in the mesial and distal tooth lobes (Fig. 1c). Between the two lobes, enamel defects were present that were located directly above the enamel–cementum junction on the buccal and lingual tooth side (Fig. 1c and d). The sharp edges of these defects suggested that they had been formed after death. In the M3, large areas of cuspal and mid-coronal enamel were covered with a mineralised deposit of a yellowish and dull appearance (Fig. 1e). Because of the presence of this covering layer, the enamel surface in these crown areas was visible only in few places. Numerous pit-type hypoplastic enamel defects were
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Fig. 1. Macroscopic appearance of the studied pig molars from Fais. (a) Palatal and (b) buccal views of M1 (FS 91-1518), arrows: hypoplastic enamel defects at the crown base, arrowheads: posteruptive enamel defects. (c) Lingual view (mesial lobe) and (d) buccal view (distal lobe) of M2 (FS 91-1526), arrows: pit-type hypoplastic enamel defects, asterisks: plane-type hypoplastic enamel defects, arrowheads: postmortem enamel defects. (e) Buccal view of central and distal lobes of M3 (FS 91-1529), extended crown areas covered with cementum (asterisks), arrow: small area of cuspal enamel surface not covered by cementum. Numerous pit-type defects are scattered over the tooth crown.
scattered over the entire tooth crown (Fig. 1e). In the more cervical crown areas, which were not or less covered by the mineralised deposit, the hypoplastic defects were more clearly visible. 3.2. Microscopic findings In the M1, both enamel and dentine exhibited accentuated incremental markings (Fig. 2a–c). Numerous accentuated striae of
Retzius (long-period incremental markings) were present in the later formed appositional and in the imbricational enamel (Fig. 2c). In contrast, the early formed appositional enamel appeared normal. Especially prominent striae (Wilson bands) were associated with the cervically located row of hypoplastic enamel defects and a plane-type hypoplastic defect located in mid-coronal enamel (Fig. 2b and c). The Wilson bands, which were characterized by the presence of aprismatic enamel, were exposed at the bottom of the
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Fig. 2. Axiobuccopalatally sectioned mesial lobe of M1, cuspal to top of images. (a) Ground section viewed in ordinary transmitted light; note accentuated incremental markings (asterisk) in the inner (later formed) dentine (D). E: enamel. (b) SEM–BSE image of cervical tooth region showing porosity of enamel (E) and a Wilson band (arrow) with aprismatic enamel associated with a hypoplastic enamel defect (asterisk); numerous diagenetic foci are present in the dentine (D), note frequent occurrence of hypermineralised rims in the diagenetic foci. (c) Ground section through imbricational buccal enamel viewed in transmitted light with phase contrast; arrows indicate a Wilson band associated with a hypoplastic defect (arrowhead) in cervical enamel, asterisk: plane-type hypoplastic enamel defect; D: dentine; E: enamel.
associated hypoplastic defects (Fig. 2b). Occurrence of aprismatic enamel denotes matrix secretion by ameloblasts lacking the distal (prism-forming) portion of their Tomes’ process. The course of a Wilson band marks the position of the enamel-forming front at the time of an insult to the secretory stage ameloblasts, which led to an either permanent or transient disruption of matrix secretion. Large portions of the enamel of the M1 exhibited an abnormally high porosity. In cuspal enamel, this porosity was confined to approximately the outer third of the tissue, whereas in the cervical crown area, the entire enamel layer was affected (Fig. 2b). A prominent structural feature of the first molar’s dentine was an accentuation of the long-period incremental markings (Andresen lines), which became increasingly more marked in pulpal direction (Fig. 2a). In addition, extended bands of interglobular dentine, i.e., of areas of unmineralised or severely hypomineralised dentinal matrix
where calcospherites had failed to fuse, were present predominantly in the inner half of the dentine layer, located nearer to the pulp cavity (Fig. 3a and b). The interglobular spaces appeared black in BSE images, thereby indicating their lack of mineral. Numerous diagenetic foci with varying mineral density were present in the dentine (Figs. 2b and 3b, d). While the core areas of these diagenetic foci were often hypomineralised (appearing darker on BSE images), their edges sometimes appeared bright, thereby revealing that they were hypermineralised compared to the surrounding dentine (Figs. 2b and 3b). The diagenetic foci could easily be distinguished from the interglobular spaces by both, the formers’ higher mineral density and differences in morphology (Fig. 3b). SE imaging of the etched polished block surface of the M1 revealed that the dentinal tubules contained structures identified as odontoblast processes. In circumpulpal dentine the diameter of these
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Fig. 3. Axiobuccopalatally sectioned mesial lobe of M1, cuspal to top of images. (a) and (b) SEM–BSE images, (c) and (d) SEM–SE images (etched section). (a) Bands of interglobular spaces in circumpulpal dentine. (b) Detail showing unfused calcospherites (arrows) separated by interglobular spaces. Asterisks: diagenetic foci. (c) Odontoblast processes (arrows) in the dentine. (d) Higher magnification showing interglobular spaces (asterisk), odontoblast processes (arrows) with small lateral branches, and tunnelling tubes (arrowheads) preferentially orientated perpendicularly to the dentinal tubules.
processes, which exhibited small lateral branches typical of odontoblast processes, was between 2.0 and 2.5 mm (Fig. 3c and d). The processes were not visible on BSE images, thereby demonstrating that they had not been mineralised as part of a diagenetic process (Fig. 3b). In the SE images, the interglobular spaces appeared as voids bridged by the odontoblast processes (Fig. 3d). It further became apparent that the diagenetic foci contained branched tubular tunnelling structures diagnosed as microbial infiltrates (Fig. 3d). The principal direction of these tunnelling tubes was perpendicular to the course of the dentinal tubules, i.e., they were preferentially orientated in the same direction as the incremental structures of the dentine. Some of the tubes, however, ran parallel to, and occasionally presumably also within the dentinal tubules. In places, rounded end buttons were associated with the leading tubes (Fig. 3d). No indication of formation of reactive or reparative dentine was encountered at the dentine mineralisation front (Fig. 3a), indicating that microbial infiltration into the dentine of the M1 had occurred as a diagenetic process. In the M2, strongly accentuated incremental markings were found in the entire enamel and dentine (Fig. 4a). In the enamel, which exhibited a ‘‘cloudy’’ brownish to blackish colouration when viewed in ordinary transmitted light, several Wilson bands were associated with different types of hypoplastic defects (Fig. 4a and b). Cuspally, the peripheral enamel layer exhibited an abnormally high porosity, while the inner enamel showed a higher mineral density. In cervical direction, the area of porous enamel increased in thickness (Fig. 4b), with the cervical enamel being almost
completely affected by this condition. The reduced mineral content of the enamel was more pronounced in the prisms compared with the interprismatic enamel (Fig. 4c). In the outer enamel, fine parallel lines oriented perpendicular to the course of the enamel prisms were seen in both prisms and interprismatic enamel (Fig. 4c). These lines are regarded to represent short-period (daily) incremental markings. The dentine of the M2 showed prominent Andresen lines (Fig. 4a). Extended bands of interglobular dentine were, however, not encountered in this tooth. Postmortem changes in the dentine of the M2 were similar but less pronounced than those recorded in the dentine of the M1. The enamel of the M3 was severely hypomineralised and exhibited the most pronounced structural abnormalities of the three studied teeth. In the light microscope, a marked accentuation of the striae of Retzius pattern was discernible (Fig. 5a and b). Several Wilson bands were associated with pit- and plane-type hypoplastic defects (not shown). The outer enamel was severely hypomineralised, except for an outermost rim of aprismatic enamel exhibiting a somewhat higher mineral content (Fig. 6a–d). The more central enamel underneath the porous outer zone was characterized by numerous, irregularly arranged larger clefts (Fig. 6a). From this area, smaller clefts extended into both, the outer and inner enamel. The clefts most likely originated from the shrinkage of the hypomature enamel, containing a high percentage of organic matrix and water, during drying of the teeth.
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Large areas of the cuspal and mid-coronal enamel of the M3 were covered by a mineralised deposit of mostly approximately 100 mm thickness Figs.(5a, b and 6a, b). In places, however, sharply demarcated cavitary lesions were present in the enamel surface that were completely filled with this mineralised deposit (Figs. 5a, b and 6c). The striae of Retzius did not change their course according to the contour of these cavities (Fig. 5a and b), thereby denoting that the latter did not represent hypoplastic defects. Rather, the cavitary lesions were diagnosed to have been caused by a (pre-eruptive) resorption of enamel. In BSE images, the deposits that occluded the cavities appeared less mineralised than the porous outer enamel (Fig. 6a–d). The mineralised deposits contained numerous lacunae, and sometimes small canaliculi were discernible that originated at these lacunae (Fig. 6b and c). Thus the overall appearance of the deposits was that of cellular cementum. In places, larger voids were present within the cementum (Fig. 6c and d). These voids are regarded to represent either vascular channels within, or hypoplastic defects of, the coronal cementum. In many areas, the cementum was heavily infiltrated by filamental structures diagnosed as microorganisms (Fig. 6d). The cementum surrounding the infiltrated areas often appeared hypomineralised (Fig. 6c and d). Interestingly, the microorganismal invasion had not spread into the underlying enamel. The dentine of the M3 showed massive alterations due to diagenetic processes and mostly appeared opaque and blackish when viewed in ordinary transmitted light. However, in some areas less affected by diagenesis, a strong accentuation of the pattern of Andresen lines was discernible (not shown). 4. Discussion The studied teeth exhibited a variety of abnormalities that were caused either by disturbances of dental hard tissue formation or by diagenesis in the soil-embedded teeth. The recorded developmental defects in the enamel denote a marked disturbance of both, the secretory stage and the maturation stage of enamel formation. The high synthetic and secretory activity of the secretory stage ameloblasts renders them particularly susceptible to a disturbance of cell function. Structural abnormalities that can be attributed to an impairment of the secretory stage of amelogenesis were the overall accentuation of the incremental pattern, the occurrence of Wilson bands, i.e., of grossly accentuated long-period incremental lines with a disrupted enamel microstructure, and the presence of hypoplastic enamel defects (Kierdorf and Kierdorf, 1997; Kierdorf et al., 2000, 2004; Witzel et al., 2006). The increased enamel porosity, observed in all three teeth, is indicative of a disturbance of enamel maturation. During enamel maturation, breakdown and removal of enamel matrix is followed by intense crystallite growth, by which the high mineral content of mature enamel is achieved (Nanci, 2008). Increased porosity of enamel has previously been reported as a developmental defect related to excess fluoride exposure in teeth of humans and other mammals (Richards et al., 1986, 1992; Suckling et al., 1988; Fejerskov et al., 1996; Kierdorf et al., 1997, 2004). Because in the present study soil-embedded teeth were analyzed, some contribution of diagenetic processes to the observed Fig. 4. Axiobuccolingually sectioned mesial lobe of M2, cuspal to top of images. (a) Ground section viewed in ordinary transmitted light; discolouration of the enamel (E), and accentuated incremental markings in enamel and dentine (D); a plane-type hypoplastic enamel defect (asterisk) is associated with a Wilson band (arrows). (b) SEM–BSE image of buccal enamel exhibiting a plane-type hypoplastic defect (asterisk), note the presence of a Wilson band (arrows) and of aprismatic enamel (arrowhead). The outer enamel exhibits increased porosity compared with deeper enamel areas. (c) Higher magnification of the porous outer enamel shown in (b); note fine parallel striation in prisms and interprismatic enamel (arrows).
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Fig. 5. Axiobuccolingually orientated ground section through mesial lobe of M3 viewed in ordinary transmitted light, cuspal to top of images. (a) Enamel (E) covered with a layer of coronal cementum (C), note resorption cavities obliterated with cementum (asterisks) and striae of Retzius being cut by the cavity margins. (b) Large resorption cavity in enamel (E) filled with coronal cementum (C), note that the striae of Retzius do not bend according to the contour of the cavity wall.
increased enamel porosity cannot be ruled out. Such diagenetic effects on the mineral content of enamel have been described as pseudocaries in human teeth of Palaeolithic and Mesolithic age (Poole and Tratman, 1978). Using atomic force microscopy, Dauphin et al. (2007) recently demonstrated diagenesis at the level of enamel crystallites from fossil teeth of the suid species Kubanochoerus massai, whose enamel microstructure appeared unaltered on inspection with the scanning electron microscope. Intravital and postmortem penetration of stains into the porous enamel is seen as the cause for its abnormal colouration. The compromised mechanical stability of the hypomineralised porous enamel caused the observed intravital loss of larger areas of surface enamel, this observation again matching findings in hypomineralised fluorotic enamel (Fejerskov et al., 1996; Kierdorf et al., 1996, 2004; Aoba and Fejerskov, 2002). In the M3, an overall hypomaturation of the enamel was deduced from our findings. The most hypomature enamel was located deep to an enamel layer of somewhat higher mineral density. The clefts recorded in the severely hypomature enamel are regarded to represent shrinkage artefacts. A particularly interesting finding in the M3 was the presence of a layer of cementum covering large areas of the tooth crown. Normally pig teeth, like human teeth, are free of coronal cementum, except for the occasional occurrence of small cementum tongues or spurs extending over a small distance from the root cementum onto the cervical crown portion (Schroeder, 1992; Kierdorf et al., 2005). In contrast, in mammals with high-crowned teeth, including cattle, sheep, goats, horses, and rabbits, the crowns of the cheek teeth and, in some species, also those of the front teeth are covered by a welldeveloped layer of cementum to varying degrees (Weinreb and Sharav, 1964; Mills and Irving, 1967; Listgarten, 1968; Listgarten and Kamin,1969; Jones and Boyde,1974; Kilic et al.,1997). Several studies have demonstrated that in these species a prerequisite for the formation of coronal cementum is a disintegration of the reduced enamel epithelium prior to the completion of enamel maturation (Weinreb and Sharav, 1964; Mills and Irving, 1967; Listgarten, 1968; Listgarten and Kamin, 1969; Jones and Boyde, 1974), thereby
permitting contact of mesenchymal cells of the dental follicle with the enamel surface. Experimental studies indicated that the formation of coronal cementum is triggered by the exposure of these mesenchymal cells to the surface of the immature enamel. Thus, removal of the enamel epithelium from molar tooth germs of mice was followed by the formation of cementum onto the exposed enamel surface (Heritier, 1982). Based on more recent experimental evidence, it has been suggested that the differentiation of mesenchymal cells into cementoblasts is induced by the exposure of the cells to matrix proteins of the immature enamel (Hammarstro¨m, 1997; Spahr and Hammarstro¨m, 1999; Handa et al., 2002). Occurrence of coronal cementum has in certain pathological conditions previously been described in human and pig teeth. In human teeth, coronal cementum was found in embedded teeth (Kota´nyi, 1924; Kronfeld, 1938; Arwill, 1974), in cases of amelogenesis imperfecta (Weinmann et al., 1945; Listgarten, 1967), and in enamel pits and fissures of unerupted and erupted teeth (Sillness et al., 1976; Kodaka and Debari, 2002). Formation of coronal cementum in pigs was reported in teeth with severe enamel hypoplasia (Kierdorf et al., 2005; Witzel et al., 2006). In these cases it was suggested that a serious disruption of enamel formation had caused a partial or complete premature disintegration of the enamel epithelium. In line with this interpretation, a partial premature breakdown of either the reduced enamel epithelium or a partial demise of the enamel organ at an earlier stage of enamel formation is assumed to have occurred in the pig M3 from Fais. Both scenarios would be consistent with the observed enamel hypomaturation of this tooth. Presence of resorption cavities in the enamel of the M3 indicates that in places the surface enamel had been resorbed prior to the deposition of the cementum. Instances of pre-eruptive resorption of enamel by odontoclasts prior to the formation of coronal cementum have been reported for embedded human teeth (Kronfeld, 1938; Boyle, 1955; Schmidt and Keil, 1958). Witzel et al. (2006) described structures resembling resorption cavities in the enamel surrounding a large hypoplastic defect of a pig molar that was partly covered by coronal cementum. While in the above cases,
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Fig. 6. Axiobuccolingually sectioned mesial lobe of M3, SEM–BSE images. (a) Cuspal enamel (E) covered with cementum (C); a broad zone of enamel exhibiting numerous clefts is sandwiched between an outer and an inner layer of less severely altered enamel. (b) Higher magnification of outer enamel and covering cementum layer; cementocyte lacunae (arrows) are visible in the cementum (C), indicating its cellular nature; the outermost enamel (arrowhead) appears aprismatic and more highly mineralised than deeper enamel layers. (c) Hypomineralised enamel (E) with a large resorption cavity filled with cementum (C); the cementum exhibits a large void (asterisk) regarded to represent either a vascular space or a hypoplastic defect, and diagenetic foci (arrows). (d) Outer enamel (E) and coronal cementum (C) with massive infiltration by microorganisms (arrow); note voids in the cementum. Arrowhead: surface layer of aprismatic enamel.
enamel resorption occurred as part of a pathological process, Jones and Boyde (1974) found that in the horse, a species in which coronal cementum is normally present, cementum deposition is apparently regularly preceded by odontoclastic resorption of enamel. They suggest that this process leads to a better attachment of the cementum to the enamel surface. The massive invasion of microorganisms into the coronal cementum of the M3 is thought to have taken place while the tooth was embedded in the soil. Interestingly this invasion did not spread into the enamel, thereby corroborating the view (Bell et al., 1991) that of the dental hard tissues, enamel is least affected by microorganismal attack during diagenesis. The dentine of all analyzed teeth exhibited severe developmental defects as well as marked postmortem changes. In all three molars, an accentuation of the Andresen lines was observed. In the inner half of the dentine of the M1, multiple rows of interglobular dentine were present. Interglobular dentine represents areas where the mineralising globules (calcospherites) have failed to grow large enough to coalesce and thereby to mineralise the entire predentine matrix (Hillson, 2005). The fact that the more peripheral dentine of the M1 (near the enamel–dentine junction) did not exhibit mineralisation defects indicates that during early dentine formation the mineralisation process had not been (markedly) impaired. There is experimental evidence (Spreter von Kreudenstein, 1939; Jenkins, 1978; Kagayama et al., 1997) that the formation of interglobular dentine is associated with a concomitant disturbance of enamel maturation. The occurrence of hypomineralised enamel areas and zones of interglobular dentine in the pig molars from Fais
thus points to a generalised impairment of dental hard tissue mineralisation in the animals. Numerous diagenetic foci were present in the dentine of the studied teeth. These foci presented as areas of varying degrees of hypomineralisation compared with the surrounding unaffected dentine. However, some of the diagenetic foci had hypermineralised rims, thereby matching observations by Bell et al. (1991) and Hillson (2005). These hypermineralised rims may result from a re-precipitation of previously dissolved mineral. Tunnelling microbial invasion was seen in the dentine of the M1, with the principal direction of the tunnelling tubes being perpendicular to the course of the dentinal tubules, i.e., orientated corresponding to the incremental structures. Microbial (bacterial and/or fungal) invasion has previously been reported for archaeological teeth (Sognnaes, 1955; Falin, 1961; Poole and Tratman, 1978; Bell et al., 1991; Turner-Walker, 2008) and bone (Marchiafava et al., 1974; Hackett, 1981; Jackes et al., 2001; Schultz, 2001; Hedges, 2002; Jans et al., 2004; Turner-Walker, 2008). So far, the organisms responsible for this invasion have not been properly identified (Turner-Walker, 2008). Poole and Tratman (1978) argue that saprophytic actinomycetes are likely candidates, while in case of archaeological bone, Jackes et al. (2001) tentatively identified Clostridium histolyticum as the destructive bacterium. In contrast, Turner-Walker (2008) argues that aerobic bacteria seem to be involved in the microbial destruction of bone in normal (i.e. not waterlogged) archaeological soils. Interestingly, preservation of the odontoblast processes was diagnosed in the dentine of the M1. This indicates that under certain
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conditions, organic structures can be preserved over longer periods in archaeological teeth. Similar observations were reported by Falin (1961), who found evidence of preserved odontoblast processes in dentinal tubules of human teeth from the Bronze Age. However, there is a caveat regarding the diagnosis of soft tissue preservation in archaeological and fossil bones and teeth since it has been reported that endocasts originating from bacterial biofilms can mimic soft tissue preservation in fossil bone (Kaye et al., 2008). The recorded morphological details (i.e. bridging of the interglobular spaces by the odontoblast processes and the presence of small lateral branches), however, suggest that in the case of the studied M1 we are actually dealing with a case of true soft tissue preservation. This is an interesting finding since it points to the likely preservation of ancient biomolecules (e.g. aDNA) in such specimens. The developmental defects in enamel and dentine of the studied pig teeth denote a marked disturbance of dental hard tissue formation. A wide variety of systemic influences, among them mineral (calcium, phosphorus and magnesium), hormonal (vitamin D) and general nutritional deficiencies, are known to disturb dental hard tissue formation (Mellanby, 1929, 1930; Spreter von Kreudenstein, 1939; McCance et al., 1961; Tonge and McCance, 1965, 1973; Yaeger, 1966; Jenkins, 1978; Furuta et al., 1999; Schroeder, 1991; Moseley et al., 2003). Intoh and Shigehara (2004) previously hypothesized that the tooth defects in the pigs from Fais had been caused by periods of severe nutritional stress. This assumption gains support from the experimental findings of Tonge and McCance (1965). These authors reported developmental defects of enamel and dentine in the teeth of pigs that had been severely undernourished over a prolonged period of time. The defects described by Tonge and McCance (1965) resemble those found by us in the pig molars from Fais, except that formation of coronal cementum was not reported for the experimental pigs. Crown formation of pig first molars starts in utero, covers the period of milk-feeding and is completed at approximately three months postpartum. Crown formation in the M2 starts at about 2–3 months postpartum and mainly takes place after weaning, whereas crown formation of the third molars occurs completely after weaning (McCance et al., 1961; Tonge and McCance, 1965, 1973; Davies, 1990). Presence of severely hypomature enamel and of coronal cementum covering this enamel indicates that enamel formation in the M3 from Fais was apparently more strongly disrupted than in the M1 and M2. The observation that the recovered deciduous pig premolars from Fais were free of enamel hypoplasia (Intoh and Shigehara, 2004) moreover suggests a low stress level during the crown formation period of these teeth. Variation in stress intensity during the formation of the permanent dentition can also be deduced from the fact that in the M1 the early (prenatally and early postnatally) formed enamel and dentine exhibited no or less severe developmental defects than the later formed enamel and dentine. It is therefore hypothesized that the prenatal and early postnatal (period of milk-feeding) stages of tooth formation where to some extent protected against the presumed nutritional stress, while later (postweaning) stages were no longer ‘‘buffered’’ against this disturbance. The fact that the M3 showed the most pronounced developmental defects is in accordance with the view that the postweaning stages of dental development occurred under conditions of severe stress. The histological results of the present study are thus consistent with the hypothesis of Intoh and Shigehara (2004) that the pigs on the small, resource-limited island of Fais experienced severe nutritional stress. Since pigs on small Pacific islands are mainly fed with copra and some vegetable scraps only (Intoh and Shigehara, 2004), a general condition of malnutrition is likely to occur in the animals after weaning. The dietary situation of domestic pigs may be further aggravated during severe draught periods known to occur from time to time in the area. However, also other factors that severely affect
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the health of postweaning pigs could potentially cause developmental defects in teeth forming partly or completely after weaning. Today, one such factor that leads to morbidity and mortality in pigs worldwide is postweaning diarrhoea, which is caused by enterotoxigenic strains of Escherichia coli (Fairbrother et al., 2005). 5. Conclusion and outlook Our results demonstrate a severe disturbance of dental hard tissue formation in the pigs from Fais. The lack of (macroscopic) defects in deciduous premolars, and the microscopic findings in the M1 suggest that prenatal and early postnatal stages of tooth formation were largely protected against the stress impact causing a disturbance of normal dental development. Our findings are consistent with the hypothesis that the pigs on Fais suffered from severe nutritional stress after weaning (Intoh and Shigehara, 2004). In addition to developmental defects, the analyzed pig molars exhibited different postmortem changes. All three dental hard tissues were affected by diagenesis, although to varying degrees. Microscopic analysis mostly enabled a differential diagnosis of developmental defects and postmortem changes. However, the relative contribution of diagenesis to the observed increased porosity of the enamel could not be determined exactly. An ongoing field survey (Dobney et al, unpublished observation) of archaeological pig dentitions from a number of islands in Micronesia and East Polynesia indicates a high frequency of coronal cementum formation in the molars along with the presence of severe hypoplastic enamel defects in permanent (and in some cases even deciduous) teeth. Although analyses of the frequency, severity and chronology of these developmental defects has as yet not been completed, it is clear that major long-term disruption to the development of the dental hard tissues occurred in the domestic pig populations introduced into Oceania by prehistoric and later settlers (Larson et al., 2007). Given the interpretation of the developmental defects as being caused by severe nutritional stress, it seems promising to study this pathology as an indicator for the living conditions of domestic pigs across the Pacific region, and thereby to contribute to the reconstruction of certain aspects of island subsistence economy on a wide geographical scale. Acknowledgements The authors gratefully acknowledge the expert technical help of D. Klosa (Geozentrum Hannover) with BSE–SEM imaging. References Aoba, T., Fejerskov, O., 2002. Dental fluorosis: chemistry and biology. Critical Reviews in Oral Biology and Medicine 13, 155–170. Arwill, T.A., 1974. A qualitative microradiographic study of the enamel and the dentine in ground sections of impacted permanent teeth. Acta Odontologica Scandinavica 32, 1–13. Bell, L.S., Boyde, A., Jones, S.J., 1991. Diagenetic alterations to teeth in situ illustrated by backscattered electron imaging. Scanning 13, 173–183. Boyle, E., 1955. Kronfeld’s Histopathology of the Teeth and Their Surrounding Structures, fourth ed. Lea & Fiebiger, Philadelphia. Carter, R., Magnell, O., 2007. Age estimation of wild boar based on molariform mandibular tooth development and its application to seasonality at the Mesolithic site of Ringkloster, Denmark. In: Albarella, U., Dobney, K., Ervynck, A., Rowley-Conwy, P. (Eds.), Pigs and Humans – 10,000 Years of Interaction. Oxford University Press, Oxford, pp. 197–217. Dauphin, Y., Montuelle, S., Quantin, C., Massard, P., 2007. Estimating the preservation of tooth structures: towards a new scale of observation. Journal of Taphonomy 5, 43–56. Davies, A.S., 1990. Postnatal development of the lower canine and cheek teeth of the pig. Anatomia Histologia Embryologia 19, 269–275. Dobney, K., Ervynck, A., 2000. Interpreting developmental stress in archaeological pigs: the chronology of linear enamel hypoplasia. Journal of Archaeological Science 27, 597–607.
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