Bones in the skull are separated by sutures - a kind of joint made up of soft tissues, and thus a soft area compared to rigid bones. Sutures are found to be important growth sites, yet their biomechanical significance is an open question, because their function during chewing activities is unclear, and the effects of their fusion status and placements have not being systematically studied.   

It is hypothesized that sutures act as energy absorbers protecting skulls. In order to test this hypothesis, biomechanical and morphometric analyses were conducted to examine, [1] the biomechanical impact of craniofacial sutures with under different conditions with variants including sutural fusion status, sutural elastic properties, and loading regimes, and [2] morphological impact of the placement of sutures.     

First, the biomechanical effects of sutures were tested using Finite Element Analysis, a powerful computer-aided program that allows the modeling of sutures in the context of an assessment of synchronous global strain patterns using various loading designs.  [1] Static Analysis - Using loading simulations corresponding to incisor, premolar, and molar maximal biting conditions,  a sensitivity analysis of the mechanical effect of sutures in Finite Element models of a macaque cranium with eight bone-suture functional units representing eight facial sutures.  . Results demonstrate that the presence of sutures does not profoundly influence global strain patterns, regardless of their material properties and fusion status (Fig. 1). More specifically, strain patterns remained relatively unaffected away from the suture sites, and bite reaction force was likewise barely affected. Thus, the biomechanical significance of sutures in a global context would therefore appear to be limited.  [2] In simulation of physiological dynamic loading conditions, the biomechanical effects of the zygomaticotemporal suture in a juvenile Rhesus macaque cranium were tested (Fig. 2). The dynamic analyses produced similar results compared to static simulations in terms of strain patterns and reaction forces, indicating that the zygomaticotemporal sutures have limited impact on global skull mechanics regardless of loading design (Fig. 4).  Thus, contrary to the functional hypothesis tested, sutures did not absorb significant amounts of energy during either static or dynamic simulations. 

Second,  based on findings from mechanical simulations of sutures, it is alternatively hypothesized that sutures are mechanically significant only insofar as they are weak points on the cranium that must be shielded from unduly high stresses so as not to disrupt vitally important growth processes. This derived hypothesis is tested in two projects. [1] The placement of a facial suture in the face (maxilla-zygomatic suture/MZS) was investigated in Old World Monkeys (OWM) and New World Monkeys (NWM). Results demonstrated that the MZS in NWM has a more lateral position compared to that in OWM.  Consequently, the ratio of facial surface vs. temporal surface of the zygoma in NWM is relatively smaller than that in OWM, which is coupled with different configuration patterns in the orbital and pterion areas. Variation is also present within closely related taxa.  For example, the MZS is more laterally placed in Cebus apella than in C. albifrons. These findings suggest different bone interaction patterns related to differences in dietary ecology. The significance of the placement of sutures thus warrants careful ontogenetic, phylogenetic, and biomechanical studies. [2] The impact of naturally developed extra sutures in the highly stressed in the midface, such as the zygoma (divided zygoma with intrazygomatic suture), which is a naturally-happened experiment defy...

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