Determining primates bite force from histological tooth sections

Abstract

Objectives The ability to accurately estimate bite force (BF) in extant and fossil primates is valuable to biological anthropologists. BF is generally evaluated using complex jaw musculature and lever arm analyses employing numerous assumptions and requiring complete cranial morphology. Here, a simple method to determine BF from data measured on histological sections of fossil teeth is proposed. Methods Published sections of molar teeth encompassing 27 different extinct and extant primates dating back to as early as 17 million years ago were examined. Focusing on the cusp region, the extracted data include characteristic enamel thickness dc and dentin horn angle φ. The occlusal force needed to fracture a cusp, PF, was determined from these variables with the aid of a finite element stress analysis similarly to a previous study on postcanine human teeth. The bite force was obtained by linking BF to PF using a universal constant. Results The measured variables dc and φ are conclusively linked. This link produces a virtually constant fracture force PF and in turn bite force BF for all cusps in the molar row. An explicit formula tying BF to dc and φ was derived. For nonhominin taxa the bite force, molar crown area, and body mass are found to be intimately related. The case of hominins is more involved. The so determined BF is gender‐averaged, with the bite force of males estimated to be ≈12% greater than that of females. Conclusions The use of “fracture mechanics” concepts from mechanics of materials facilitates determination of critical bite force in primates based on characteristic enamel thickness dc and dentin horn angle φ as extracted from histological sections of molar teeth. This novel approach enables quantitative insight into the role played by crown area, body mass and bite force on evolutionary trends. The conclusive link between cuspal enamel thickness and dentin horn angle facilitates optimal food processing without hindering cusp resilience. The proposed approach may be extended to mammals having asymmetric cusp structures.

Chipping and wear patterns in extant primate and fossil hominin molars: ‘Functional’ cusps are associated with extensive wear but low levels of fracture

“…Because these same enamel side differences are a common feature in primates (Ulhaas et al, 1999), additional protection for functional cusps may help explain the lower levels of chipping in these positions. However, a recent study suggests fracture resistance may be maintained between functional and nonfunctional cusps, despite differences in enamel thickness, through changes in the dentin horn angle (Chai, 2020).…”

Estimates of absolute crown strength and bite force in the lower postcanine dentition of Gigantopithecus blacki

“…These teeth are now stored in the Anthropology Museum of Guangxi, China. Comparative data for molar ACS and molar BF were compiled from the literature (Skinner et al, 2015;Chai, 2020;Schwartz et al, 2020) and are provided in SOM Tables S1 and S2. The samples of extant great apes include Pan paniscus, Pan troglodytes, Pongo sp., and Gorilla sp.…”

“…5). Given that the DHA is <150° for most hominid teeth (Chai, 2020), it is assumed that a positive relationship between φ and q holds in most cases. Since both safety factors and the material-related parameter A0 are assumed to be independent of taxon, Chai (2018) assumed that BF is mainly controlled by DHA and CET.…”

“…For instance, in both cases, the enamel cracks extended from the EDJ and the peak stress occurred near the EDJ. Thus, despite underlying assumptions and limitations, the simplifications in the numerical model were deemed acceptable (Chai, 2018(Chai, , 2020. Although there are other methods to estimate BF, most require cranial material (e.g.…”

Sagittal suture strain in capuchin monkeys (Sapajus and Cebus) during feeding

“…and the untufted forms represent Cebus sp. The more robust morphology of Sapajus relative to Cebus is characterized by larger teeth, thicker mandibular corpora and symphyses, prominent and anteriorly positioned feeding muscles, greater temporalis physiological cross‐sectional area, and more sinuous sagittal sutures (Figure 1; Anapol & Lee, 1994; Byron, 2009; Chai, 2020; Daegling, 1992; Kinzey, 1974; Masterson, 1997; Hogg and Elokda, 2021; Silva Jr., 2001, 2002; Spencer, 2003; Taylor & Vinyard, 2009; Teaford et al, 2020; Wright, 2005). These features are probable adaptations for consumption of tougher foods in Sapajus relative to Cebus , and a seed predation strategy including obdurate foods, such as palm nuts (Cole, 1992; Defler, 1979a; Defler, 1979b; Freese et al, 1981; Izawa, 1979; Kinzey, 1974; Teaford, 1985; Teaford et al, 2020; Wright, 2005).…”