The Global Impact of Sutures Assessed in a Finite Element Model of a Macaque Cranium

Abstract

The biomechanical significance of cranial sutures in primates is an open question because their global impact is unclear, and their material properties are difficult to measure. In this study, eight suture-bone functional units representing eight facial sutures were created in a finite element model of a monkey cranium. All the sutures were assumed to have identical isotropic linear elastic material behavior that varied in different modeling experiments, representing either fused or unfused sutures. The values of elastic moduli employed in these trials ranged over several orders of magnitude. Each model was evaluated under incisor, premolar, and molar biting conditions. Results demonstrate that skulls with unfused sutures permitted more deformations and experienced higher total strain energy. However, strain patterns remained relatively unaffected away from the suture sites, and bite reaction force was likewise barely affected. These findings suggest that suture elasticity does not substantially alter load paths through the macaque skull or its underlying rigid body kinematics. An implication is that, for the purposes of finite element analysis, omitting or fusing sutures is a reasonable modeling approximation for skulls with small suture volume fraction if the research objective is to observe general patterns of craniofacial biomechanics under static loading conditions. The manner in which suture morphology and ossification affect the mechanical integrity of skulls and their ontogeny and evolution awaits further investi-

Cranial sutures work collectively to distribute strain throughout the reptile skull

“…However, the results are at variance with experimental and modelling studies on mammals that suggest some regions of the mammalian skull experience only very low strains during mastication [31,80]. Similarly, computer models of mammal skulls with some patent sutures do not differ significantly from skulls with no (or completely fused) sutures [52]. However, further discussion must await the analysis of a comparable mammalian skull with a full complement of patent sutures.…”

“…However, Wang et al . [52] concluded that patent sutures have little effect on skull strains in primates, and that they are perhaps less important mechanically than in animals with more patent sutures or a greater suture to bone volume, such as lizards and alligators [24,53]. Such studies combined with experimental data provide important information on suture form and function [3,23,29,30,32,54], but for a full overview of the impact of patent and fused sutures on load transfer within the skull more comprehensive analyses are necessary.…”

“…Past work has suggested that: patent sutures do not affect strain distributions [52]; patent sutures act as strain sinks and reduce strains [22,23]; sutures both reduce and elevate strains [24] and that patent sutures help modulate strains throughout the skull [30,55,56]. Here, we investigate the impact of experimental, in silico , fusion of sutures on strain magnitudes and distributions within the skull of the reptile Sphenodon by testing the following hypotheses.

Hypothesis 1: sutures have no impact on strain distribution and magnitude in the skull.

Hypothesis 2: patent sutures reduce the mean strain across the skull.

Hypothesis 3: patent sutures lead to more uniform strain distributions in the skull.

…”

The Role of the Sutures in Biomechanical Dynamic Simulation of a Macaque Cranial Finite Element Model: Implications for the Evolution of Craniofacial Form

“…Besides being important loci of craniofacial growth (Opperman, 2000), sutures are mechanically “imperfecta” in an otherwise rigid body (a cranium), and their mechanical impact has been often discussed and investigated using various experimental and computer-aided techniques in both living and fossil species (Behrents et al, 1978; Bright and Gröning, 2011; Farke, 2008; Herring, 1993; Herring and Mucci, 1991; Herring and Rafferty, 2000; Herring and Teng, 2000; Jasinoski et al, 2010a,b; Jaslow and Biewener, 1995; Kupczik et al, 2009; Kupczik et al, 2007; Lieberman et al, 2004; Moazen et al, 2009a,b; Oudhof and Van Doorenmaalen, 1983; Porro et al, 2011; Rafferty and Herring, 1999; Rafferty et al, 2003; Rayfield, 2004; 2005; Reed et al, 2011; Smith and Hylander, 1985; Sun et al, 2004; Wang et al, 2008, 2010a). Experimental studies (Behrents et al, 1978; Herring and Mucci, 1991; Herring and Teng, 2000) have demonstrated that patent sutures affect strains locally (i.e., near the suture), but practical considerations limit the ability of purely experimental studies to assess the global influence of these joints across the entire cranium.…”

Mechanics of cranial sutures during simulated cyclic loading

“…Most finite element studies involving cranial sutures use static loading conditions and assume linear elastic behaviour of the suture material (e.g., Jasinoski et al, 2010aJasinoski et al, , 2010bMoazen et al, 2009;Wang et al, 2010). However, the computational investigation by Tanaka et al (2000b) of time-dependent response in a rat suture assumed the material to be linear viscoelastic.…”