Unravelling the Functional Biomechanics of Dental Features and Tooth Wear

Abstract

Most of the morphological features recognized in hominin teeth, particularly the topography of the occlusal surface, are generally interpreted as an evolutionary functional adaptation for mechanical food processing. In this respect, we can also expect that the general architecture of a tooth reflects a response to withstand the high stresses produced during masticatory loadings. Here we use an engineering approach, finite element analysis (FEA), with an advanced loading concept derived from individual occlusal wear information to evaluate whether some dental traits usually found in hominin and extant great ape molars, such as the trigonid crest, the entoconid-hypoconulid crest and the protostylid have important biomechanical implications. For this purpose, FEA was applied to 3D digital models of three Gorilla gorilla lower second molars (M2) differing in wear stages. Our results show that in unworn and slightly worn M2s tensile stresses concentrate in the grooves of the occlusal surface. In such condition, the trigonid and the entoconid-hypoconulid crests act to reinforce the crown locally against stresses produced along the mesiodistal groove. Similarly, the protostylid is shaped like a buttress to suffer the high tensile stresses concentrated in the deep buccal groove. These dental traits are less functional in the worn M2, because tensile stresses decrease physiologically in the crown with progressing wear due to the enlargement of antagonistic contact areas and changes in loading direction from oblique to nearly parallel direction to the dental axis. This suggests that the wear process might have a crucial influence in the evolution and structural adaptation of molars enabling to endure bite stresses and reduce tooth failure throughout the lifetime of an individual.

Tooth Wear Inclination in Great Ape Molars

“…This shearing action is highly effective in breaking down food sources containing high levels of fibre. Thus, the steep wear facets found in gorillas appear to increase the shearing capabilities of their molars in order to consume a more folivorous and fibrous diet [Ungar and Williamson, 2000;Swindler, 2002;M'Kirera and Ungar, 2003;Ungar and M'Kirera, 2003;Elgart, 2010;Benazzi et al, 2013;Berthaume, 2014]. This distinct dietary difference between orangutans and the 2 African apes is further confirmed by the statistical analysis.…”

“…The OFA method has been successfully used to detect information on the diets of modern hunter-gatherer groups, fossil primates and Pleistocene humans [Ulhaas et al, 2007;Kullmer et al, 2009;Fiorenza et al, 2011cFiorenza et al, , 2015aHarvati et al, 2013;Kullmer et al, 2013;Fiorenza, 2015]. Furthermore, a few preliminary analyses have investigated the relationship between macrowear and diet in non-human primates, showing the potentials of this method [Fiorenza et al, 2014[Fiorenza et al, , 2015b.…”

Is the deciduous/permanent molar enamel thickness ratio a taxon-specific indicator in extant and extinct hominids?

“…In this sense, our study attempts to do this for the first time. While occlusal enamel topography is more directly informative in terms of functional activity and adaptive responses (e.g., Guy et al, 2013;Kono, 2004;Kono and Suwa, 2008;Olejniczak et al, 2008b), lateral enamel thickness is also involved in dissipating occlusally-related stresses (Benazzi et al, 2013a(Benazzi et al, , 2013b. Lateral enamel also resists wear, tooth height loss and maintains interproximal tooth-tooth contacts during the late stages of tooth wear after dentine exposure over the occlusal surface.…”

Exploring the biomechanics of taurodontism

“…Benazzi et al. , ,b, ), a preliminary step for FEA requires the identification of contact areas between the RM 1 and the antagonistic teeth during a two‐body interaction, i.e. tooth–tooth contact, which might be more damaging to the tooth crown than food–tooth contacts, because more localized stresses increase (Lucas, ).…”

“…; Benazzi et al. , , ,b, ) to load the lower right first molar (RM 1 ) of Le Moustier 1. The analysis was carried out on the digital volumetric model of the original specimen and on the digital models of a shortened and a hyper‐taurodontic version of Le Moustier RM 1 to emphasize the differences (in displacements and stress distribution), if any, between the original and two extreme manipulated root shapes.…”