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Dissertation zugänglich unter
Tribology of dental enamel facets of Ungulates and Primates (Mammalia): Tracing tooth-food interaction through 3D enamel microtexture analyses
Tribologie von Zahnschmelzfacetten ausgewählter Ungulaten und Primaten (Mammalia): Rekonstruktion der Zahn-Nahrungs-Interaktion mittels 3D Schmelz-Mikrotexturanalyse
Dokument 1.pdf (7.162 KB)
Tribologie , Funktion , Primaten , Huftiere , Zahnschmelz , Mechanische Eigenschaft , Sugetiere
Freie Schlagwörter (Deutsch):
Mikrotextur , Zahn-Nahrungs-Interaktion , Biomechanik
Freie Schlagwörter (Englisch):
Microtexture , tooth-food interaction , biomechanics
Kaiser, Thomas M. (PD Dr.)
Tag der mündlichen Prüfung:
Kurzfassung auf Englisch:
The present Ph.D. thesis concerns the development of a new method of dental microtexture analysis and its application to the understanding of dental function in extant large herbivorous terrestrial mammals.
High energy uptake is required in mammals to maintain the high metabolic rate that makes the group unique. Teeth represent one of the major structural prerequisites that govern the efficiency of energy uptake. Hence teeth have played a crucial role in mammalian evolution. Moreover because they are frequently well preserved in the fossil record, methods have been developed so that the link between the dental characteristics to the foods consumed in extant species can be used as a tool to reconstruct the diets of extinct ones.
The dental microwear analysis is now a well-established tool for assessing the diets of both extant and extinct species. This method has been applied in 2D, but the recent development of 3D techniques has allowed more sophisticated quantification of surface texture patterns.
A technique of 3D automated enamel microtexture analysis, the dental areal surface texture analysis (DASTA), has been developed. It is based on standardized industrial surface texture parameters. In industrial applications these parameters are used functionally to characterize surfaces subject to wear. Parameters that robustly underscore inter-specific signals in terms of diet and chewing mechanics on enamel facets have been identified.
This methodology has been applied on two groups of herbivorous mammals. The first is composed of four ungulates: Connochaetes taurinus, Equus grevyi, Giraffa camelopardalis, and Diceros bicornis. They represent two contrasted dietary traits (browsers and grazers) and two contrasting digestive strategies (ruminant and non-ruminant). Eleven wear-related parameters characterizing textural features such as height, volume, furrows, density of peaks, and isotropy of the microtexture allow robust discrimination between grazers and browsers across digestive strategies. The tooth wear in the grazers (C. taurinus and E. grevyi) results in greater textural relief because of the higher abrasion resulting from chewing grass, whereas the browsers (G. camelopardalis and D. bicornis) have flatter tooth relief because the processing of tree leaves results in peak removal through either attrition or hydrodynamic pressures.
The second dataset is composed of eight primate species: Alouatta seniculus, Gorilla gorilla, Lophocebus albigena, Macaca fascicularis, Pan troglodytes, Papio cynocephalus, Pongo abelii, and Theropithecus gelada. Primates are mostly frugivores but supplement their diets with a diversity of food resources (seeds, grass, leaves, bark, roots, tubers, and animals). It was first tested whether the scale-sensitive fractal analysis (SSFA; Scott et al. 2005; Scott et al. 2006) can assess key properties of their diets. The complexity and heterogeneity of textures correlate with the proportion of fruits consumed. A large textural fill volume indicates that a species’s diet includes hard items, such as fruits or bark. Finally the anisotropy signal is found to relate to the ingestion of grass.
Furthermore, these food items in primate diets have different biomechanical properties than in the diets of the selected ungulates. The DASTA indicates that primates feeding on large hard items (seeds, nuts, bark) have larger textural reliefs than feeding on small hard items (grit and phytoliths). Based on the fracture and deformation theory proposed by Lucas et al. (2008) these results are interpreted as to show that large hard items fracture the enamel, whereas small hard items plastically deform it. The transition from brittle fracture to plastic deformation depends on the size of the food particle.
It was found that, besides discriminating dietary traits, industrial parameters reflect the end result of the dynamic interactions between food particles and enamel functional facets. Even though still speculative, a model is proposed to meld the results on both groups and to lay the basis for a general theory of dental wear. The DASTA points to a gradient in texture relief from leaf browsers with the flattest relief, to grazers with intermediate reliefs, to frugivores with the highest relief. The relief will be flattened in leaf browsers because of peak removal. Local fracturing will cause deep features in the textural signal of large hard object feeders (frugivores). Grazers will have intermediate reliefs because abrasives in/on grass would plastically indent the enamel surface. In ungulates with shearing action, the scars will be scratches; whereas in primates with crushing action prevailing, shallow pits will be the result. This gradient relates to interactions between food particles and enamel surfaces and to their fracture and deformation behaviors when they contact each other. This is the first step towards a universal theory of tooth wear.