Most research on primate tooth form-function relationships has focused on unworn teeth. This study presents a morphological comparison of variably worn lower second molars (M(2)s) of lowland gorillas (Gorilla gorilla gorilla; n=47) and common chimpanzees (Pan troglodytes troglodytes; n=54) using dental topographic analysis. High-resolution replicas of occlusal surfaces were prepared and scanned in 3D by laser scanning. The resulting elevation data were used to create a geographic information system (GIS) for each tooth. Occlusal relief, defined as the ratio of 3D surface area to 2D planometric area of the occlusal table, was calculated and compared between wear stages, taxa, and sexes. The results failed to show a difference in occlusal relief between males and females of a given taxon, but did evince differences between wear stages and between taxa. A lack of significant interaction between wear stage and taxon factors suggests that differences in occlusal relief between chimpanzees and gorillas are maintained throughout the wear sequence. These results add to a growing body of information on how molar teeth change with wear, and how differences between primate species are maintained at comparable points throughout the wear sequence. Such studies provide new insights into form-function relationships, which will allow us to infer certain aspects of diet in fossils with worn teeth.
"This work was subsequently expanded with the development of Kay et al.'s Shearing Quotient (SQ) (Kay, 1978; Kay and Hylander, 1978; and Kay and Covert , 1984), a measure of a tooth's relative ability to shear a food item. In addition to the highly influential SQ, a number of three-dimensional measures of surface complexity (orientation patch count) and relief have shown some success in separating primates by dietary category (e.g., Ungar and Williamson, 2000; M'Kirera and Ungar, 2003; Ungar and M'Kirera, 2003; Evans et al., 2007; Boyer, 2008; Winchester et al., 2014). All of these methods work on the principle that plant food must be broken down to a greater extent than animal-based foods for efficient digestion. "
"This finding is consistent with Ledogar et al.'s (2013) observation that dental topography differentiates platyrrhine seed predators Pithecia, Chiropotes, and Cacajao from non-seed predators Aotus and Callicebus. It also generally reflects similar findings of dental topography correlating with feeding choices in many other primate taxa (M'Kirera and Ungar, 2003; Ulhaas et al., 2004; Boyer, 2008; Bunn and Ungar, 2009; Bunn et al., 2011). "
"As noted previously our occlusal relief index (Γ) intrinsically differs from classical relief index reported in the literature (see e.g. , , , , ), but the meanings of these indices remain unclear. While a significant correlation exists between Γ and relief index (i.e., the ratio of the surface area of the enamel crown, and the surface area of the crown's projection into an occlusal plane; r = −0.91 at p<0.01), the two indices vary conversely (see Figure S6). "
[Show abstract][Hide abstract] ABSTRACT: The occlusal morphology of the teeth is mostly determined by the enamel-dentine junction morphology; the enamel-dentine junction plays the role of a primer and conditions the formation of the occlusal enamel reliefs. However, the accretion of the enamel cap yields thickness variations that alter the morphology and the topography of the enamel-dentine junction (i.e., the differential deposition of enamel by the ameloblasts create an external surface that does not necessarily perfectly parallel the enamel-dentine junction). This self-reliant influence of the enamel on tooth morphology is poorly understood and still under-investigated. Studies considering the relationship between enamel and dentine morphologies are rare, and none of them tackled this relationship in a quantitative way. Major limitations arose from: (1) the difficulties to characterize the tooth morphology in its comprehensive tridimensional aspect and (2) practical issues in relating enamel and enamel-dentine junction quantitative traits. We present new aspects of form representation based exclusively on 3D analytical tools and procedures. Our method is applied to a set of 21 unworn upper second molars belonging to eight extant anthropoid genera. Using geometrical analysis of polygonal meshes representatives of the tooth form, we propose a 3D dataset that constitutes a detailed characterization of the enamel and of the enamel-dentine junction morphologies. Also, for the first time, to our knowledge, we intend to establish a quantitative method for comparing enamel and enamel-dentine junction surfaces descriptors (elevation, inclination, orientation, etc.). New indices that allow characterizing the occlusal morphology are proposed and discussed. In this note, we present technical aspects of our method with the example of anthropoid molars. First results show notable individual variations and taxonomic heterogeneities for the selected topographic parameters and for the pattern and strength of association between enamel-dentine junction and enamel, the enamel cap altering in different ways the "transcription" of the enamel-dentine junction morphology.
PLoS ONE 06/2013; 8(6):e66142. DOI:10.1371/journal.pone.0066142 · 3.23 Impact Factor
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