Organic compositional analysis of ancient maya tooth sealants and fillings
Graphical abstract
Introduction
Ancient Mesoamerican populations modified their teeth permanently by way of filing, cutting, and drilling, while also polishing them as part of regular oral hygiene. Among the Classic Lowland Maya, dental inlays were common among elite males, with every third archaeologically-recovered individual incrusted with colorful stones and fills (Tiesler, 2022). The surface contours of the inlaid stones are varied, ranging from flat to elevated, dome shapes that appear fungiform in profile (Mata-Amado, 1995) (Fig. 1). Dental incrustation was much more complex than dental filing and followed a prescribed sequence of procedures that were performed by practitioners with a high level of skill and knowledge of tooth anatomy (Mata-Amado, 1998, Ramírez Salomón et al., 2003). Inlays were accomplished by first drilling deep yet circumferentially small openings into the labial surface of the anterior teeth, after which an inlay (typically a semiprecious stone) was fitted and, cemented into place with a sealant (Ramírez Salomón et al., 2003, Romero, 1958, Tiesler, 2022, Tiesler, 2000). Common mineral inlays include pyrite, jade, turquoise, and hematite. Less common were quartz and serpentine as dental plugs (Fastlicht, 1971, Romero, 1958, Tiesler, 1999). Amorphous materials may have been used as a part of the initial fitting or, more likely, after a stone inlay had fallen out of its socket and required refitting, needing prompt sealing to prevent dental fissuring and breakage, pain and infection (Tiesler, 2022, Tiesler, 1999).
Considering that dental inlays were originally set during early adulthood, it is remarkable that over half of the archaeologically recovered inlays were found intact, surviving both the entire life of the individual and centuries of postmortem decomposition (Fastlicht, 1971, Linné, 1950, Linné, 1948, Ramírez-Salomón, 2016, Tiesler, 2022). From a dentist’s perspective, drilling into the enamel and dentine to incorporate extrinsic material is risky, with the potential for both injury during the initial drilling as well as later carious formation (Ramírez-Salomón et al., 2018). Injuries caused by the inlay procedure include irritation and pulp damage, potentially leading to pulp necrosis and apical periodontitis, pathologies that are not only extremely painful but could lead to death (Palacios et al., 2005). It is therefore remarkable to observe the low frequencies of secondary caries among the dental inlays documented for the pre-Hispanic Maya (Fastlicht, 1976, Linné, 1950, Linné, 1948, Mata-Amado, 1998, Tiesler, 2000). Along with caries rates, pulp irritation, internal root absorption and periapical lesions were quantified in a recent radiological study of 193 Maya inlaid teeth and their bony tooth sockets (Ramírez-Salomón, 2016, Ramírez-Salomón et al., 2018). The finding of internal dentinary reabsorptions and pulpar calcifications in the cases of pulp perforation, highlights the therapeutic properties of the cementing material in this same series, with evidence of pulpar vitality even after trauma (Ramírez-Salomón, 2016). Predominately placed during early adulthood, the majority of dental inlays remained intact for the entire individual’s lifespan according to a number of regional surveys (Fastlicht, 1971, Linné, 1950, Linné, 1948, Ramírez-Salomón, 2016, Tiesler, 2022). Years ago, Linné (1950, p.167) noted that “the cement by which the filling was fixed, must have been of an extraordinary quality”, and further anticipated that “a thorough chemical investigation of the cement may solve the problem definitely”. In subsequent studies, Fastlicht (1971) explored the inorganic composition of diverse dental cements, and showed that components such as hydroxyapatite and, in some cases, a material similar to the Portland cement had been used to seal the dental cavities. Recent investigations confirmed the presence of calcium phosphates as apatite and whitlockite (Ramírez-Salomón, 2016).
The material determination of the agglutinants within these mixtures requires a set of analytic approaches that is different from inorganic material studies. Fastlich (1971) proposed vegetal resins as the likely agglutinants in Maya dental cements, though he formulated his hypothesis without organic characterization methods. An important analytic technique for the detection and classification of organic components is infrared spectroscopy (FTIR), in which complex natural products produce overlapping spectral bands resulting in a blended, yet representative plot that may be used to identify a material (Martín-Ramos et al., 2018). Likewise, attenuated total reflectance (ATR) allows the analysis of samples without prior preparation in a fast and reliable way and thus has been widely applied in archaeological studies (Bisulca et al., 2017, Chen et al., 2021, France et al., 2020, Glavcheva et al., 2014). Still better, gas chromatography coupled to mass spectrometry (GC–MS) enables the analysis of complex mixtures by allowing the separation and identification of their organic components, facilitating the identification of natural sources and biomaterials based on diagnostic molecules called biomarkers (Izzo et al., 2021). Organic compounds have been extracted and successfully characterized with GC–MS in ancient human remains (soft tissue, bones, and teeth), and remnants of attached balms and glues (Whelton et al., 2021).
In this study, we used ATR-FTIR and CG-MS organic compositional analyses to identify the chemical profiles of Classic-period Maya dental sealants and fillings. By documenting further secondary metabolites in these samples, we discuss the prepared mixtures together with their sealing, chromatic, and antiseptic properties. We further consider whether the materials used to embed and seal stone inlays may have differed from those used to fill empty dental voids. Beyond adhesive qualities, the latter was needed to guarantee that the amorphous cement volume adhered and remained securely inside the empty cavity without dissolving or crumbling. One further inquiry regards the chromatic properties of our reported dental fillings. The Maya may have intentionally colored the dental cement to replicate the colors of the original inlay: the yax (green) for jade and ek (black) for pyrite. Alternatively, the Maya may have blended the cements to create distinctive chromatic properties. For example, over half of the amorphous dental fillings surveyed across the Maya area display reddish hues, a color otherwise not evident in most stone inlays (Tiesler 2022).
Section snippets
The samples
Of the eight teeth analyzed, six are from archaeological sites in the Copan Pocket of Honduras while the other two are from Holmul, Guatemala and, Baking Pot, Belize, respectively (Fig. 2 and Table 1). The tooth sample from Baking Pot, was recovered by the Carnegie Institution (Sample 8; Bullard and Bullard, 1965, Ricketson, 1929, Willey et al., 1965). The tooth sample from Holmul, was recovered by the Peabody Museum, Harvard University (Sample 7; Merwin and Vaillant, 1932) as were two tooth
Differences between the composition of dental seals
The organic composition of the mixtures used to seal and fill empty drill cavities in the dental pieces was explored by FTIR and GC–MS analyses. While the FTIR gives an idea of the presence of certain groups of metabolites by simple inspection of the spectra (Silverstein et al., 2014), the GC offers the possibility of knowing the approximate number of compounds in the sample, which ideally corresponds to the number of peaks in the chromatogram, and also, the coupling with the MS enables the
Conclusions
The analyses conducted on dental sealings from the Maya lowlands demonstrate the rich blend of organic components in the production of ancient dental cements. Our study confirms that these were not merely agglutinants. Rather, as anticipated by Fastlicht, the Maya developed complex recipes for their dental cements to produce adhesives that not only preserved for over a millennium but likely provided hygienic and therapeutic properties. The ancient Maya dental practitioners experimented with
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This research was part of the Project titled Organic Compositional Analyses of Pre-Hispanic Maya Tooth Seals and Fillings (proposed and approved by the Peabody Museum in 2015). Proyecto CONACYT Ciencia de Frontera 61526 (titled Understanding the Sensorial Experience of Ancient and Modern Maya. New Archaeometric Studies of the Organic Compounds of Foods and Fragrances) and CONACYT Ciencia Básica 152105. The tooth sample from the site of Baking Pot, Belize, was recovered by the Carnegie
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