The mechanical significance of morphological variation in the macaque mandibular symphysis during mastication

Abstract

Catarrhine symphyseal morphology displays considerable variation. Although this has been related to dentition, phylogeny, sexual dimorphism, and facial orientation, most emphasis has been given to the functional significance of the symphysis to mechanical loading during mastication. The current state of knowledge regarding the mechanical significance of the symphysis is based on a combination of in vivo experimental and comparative studies on Macaca fascicularis. These approaches have provided considerable insight into the stereotypical patterns of loading in the symphyseal region during chewing and hypotheses related to the associated symphyseal morphologies. Finite element analysis (FEA) was used to assess how in silico manipulation translates into the mechanical loading hypotheses previously proposed experimentally. In particular, this study tests the form-function relationship of the symphysis of an adult M. fascicularis mandible during lateral transverse bending and dorsoventral shear of the mandibular symphysis, and a series of modified hypothetical morphologies including absence/presence of tori and variation in the inclination and depth of the symphysis. FEA results of this study support previous findings that stresses associated with lateral transverse bending and dorsoventral shear of the mandibular symphysis can be minimized via an increased labio-lingual thickness in the superior transverse torus, an oblique symphyseal inclination, and/or an increased symphyseal depth. The finding that reduction of strains related to lateral transverse bending and dorsoventral shear can be achieved through a number of different morphologies contributes to our understanding of the influence of morphological and/or developmental constraints, such as dental development, on symphyseal form.

Dietary Hardness, Loading Behavior, and the Evolution of Skull Form in Bats

“…These models were imported back into Mimics where we generated FE models using 10-noded tetrahedral elements (P. elongatus = 456,882 elements, A. jamaicensis = 491,547 elements). We did not segment teeth from the surrounding bone as our regions of interest were far from the dental alveolar region (Panagiotopoulou and Cobb 2011;Wood et al 2011; but see Gröning et al 2011). Following methods outlined in Dumont et al (2005), we applied constraints to the tempormandibular joints and first molar teeth to mimic deep bilateral and unilateral biting.…”

“…The physical challenges posed by such different food types are matched by a remarkable range of derived morphological and functional cranial specializations, including long and narrow snouts in nectarivorous species and very short and broad skulls in species that eat very hard fruits (Fig. 1; Wetterer et al 2000; Nogueira et al 2009; Santana et al 2010; Dumont et al 2011). For example, species that eat increasingly harder foods (fruits, vertebrates) also tend to have large temporalis muscles that have a high mechanical advantage (MA), a trend that has also evolved in other mammals that consume resistant foods such as carnivores and ungulates (Smith and Savage 1959; Davis 1964; Perez‐Barberia and Gordon 1999).…”

Interspecies difference in placement of developing teeth and its relationship with cross‐sectional geometry of the mandibular symphysis in four primate species including modern humans

“…In attempting to explain its functional significance, a number of studies have addressed the possible relationship between symphyseal shape and the mechanical stresses generated within the symphyseal region during mastication (e.g., Beecher, 1977Beecher, , 1979Hylander, 1984Hylander, , 1985Hylander, , 1988Ravosa, 1991;Daegling, 1992Daegling, , 2001Ravosa and Hylander, 1994;Fukase, 2007;Daegling et al, 2008;Fukase and Suwa, 2008;Daegling and McGraw, 2009;Koyabu and Endo, 2009;Anton et al, 2011;Groning et al, 2011;Panagiotopoulou and Cobb, 2011). Specifically, a well-developed superior transverse torus (STT) and/or an obliquely inclined symphysis seen typically in cercopithecine mandibles have been interpreted as mechanical adaptations to withstand lateral bending in the transverse plane (wishboning) during mastication, because an effective way to counter this type of bending is to increase the labiolingual thickness of the symphysis (e.g., Hylander, 1984;Ravosa, 1991;Daegling, 1992, Hylander and Johnson, 1994Panagiotopoulou and Cobb, 2011). Likewise, a prominent inferior transverse torus (simian shelf) is viewed as a structure that resists vertical bending in the coronal plane, since effective ways to counter this bending regime are to increase the height of the symphysis and to concentrate cortical bone along its inferior border (Hylander, 1985;Daegling, 2001).…”

Biomechanical Implications of Intraspecific Shape Variation in Chimpanzee Crania: Moving Toward an Integration of Geometric Morphometrics and Finite Element Analysis

“…In the field of evolutionary morphology, geometric morphometric methods (GM) have transformed the ways in which evolutionary biologists study form (Kendall, 1977;Bookstein, 1991;Slice, 2005;Adams et al, 2013). In functional anatomy, finite element analysis (FEA) has become increasingly important for testing hypotheses in human and non-human primate evolutionary biomechanics (Macho et al, 2005;Marinescu et al, 2005;Strait et al, 2005Strait et al, , 2007Strait et al, , 2008Strait et al, , 2009Strait et al, , 2013Kupczik et al, 2007Kupczik et al, , 2009Wroe et al, 2007;Wang et al, 2008Wang et al, , 2010aWang et al, ,b, 2012Gr€ oning et al, 2009;Berthaume, 2010;Panagiotopoulou, 2010Panagiotopoulou, , 2011aBenazzi et al, 2011a;2013a,b,c;Chalk et al, 2011;Dumont et al, 2011a,b;Nakashige et al, 2011;O'Higgins et al, 2011;Ross et al, 2011;Wood et al, 2011) and vertebrate biology in general (Guillet et al, 1985;Rayfield et al, 2001;Rayfield, 2004Rayfield, , 2005Rayfield, , 2011Dumont et al, 2005Dumont et al, , 2009Metzger et al, 2005;Witzel, 2004;McHenry et al, 2006McHenry et al, , 2007…”