Biomechanics of the rostrum and the role of facial sutures

Abstract

The rostrum is a large diameter, thin-walled tubular structure that receives loads from the teeth. The rostrum can be conceptualized both as a rigid structure and as an assemblage of several bones that interface at sutures. Using miniature pigs, we measured in vivo strains in rostral bones and sutures to gain a better understanding of how the rostrum behaves biomechanically. Strains in the premaxillary and nasal bones were low but the adjacent maxillary-premaxillary, internasal, and intermaxillary suture strains were larger by an order of magnitude. While this finding emphasizes the composite nature of the rostrum, we also found evidence in the maxillary and nasal bones for rigid structural behavior. Namely, maxillary strain is consistent with a short beam model under shear deformation from molar loading. Strain in the nasal bones is only partially supported by a long beam model; rather, a complex pattern of dorsal bending of the rostrum from incisor contact and lateral compression is suggested. Torsion of the maxilla is ruled out due to the bilateral occlusion of pigs and the similar working and balancing side strains, although it may be important in mammals with a unilateral bite. Torsional loading does appear important in the premaxillae, which demonstrate working and balancing side changes in strain orientation. These differences are attributed to asymmetrical incisor contact occurring at the end of the power stroke.

Mechanical Influences on Suture Development and Patency

“…Cyclic functional loading also features variable, but often high magnitudes of strain. As illustrated in figure 1, mastication in pigs can strain sutures up to 2,000 με, either in compression (nasofrontal) or tension (zygomatic, premaxillary-maxillary) [22,38]. Stiffness, viscoelasticity and fatigue resistance would all affect the ability of a suture to deal with cyclic loads.…”

Masticatory muscles and the skull: A comparative perspective

“…13 In fact, the only part of the pig skull that strains differently depending on the side of chewing is the premaxillary, because incisor occlusion, unlike molar occlusion, is one-sided. 19 Like occlusal force, TMJ loads are reactions to muscle pull. The balance between occlusal and joint force is a product of muscle anatomy and contraction pattern.…”

Using finite‐element analysis to investigate suture morphology: A case study using large carnivorous dinosaurs

“…Strains within sutures are notably larger than bone strains (Behrents et al, 1978;Smith and Hylander, 1985) and may reach an order of magnitude greater (Jaslow and Biewener, 1995;Rafferty et al, 2003). Strains appear to be modulated across sutures (Herring et al, 1996;Thomason et al, 2001) such that in the postsuture strain environment, strains are partially transmitted, reorientated, or damped.…”

“…Strains appear to be modulated across sutures (Herring et al, 1996;Thomason et al, 2001) such that in the postsuture strain environment, strains are partially transmitted, reorientated, or damped. During dynamic loading, sutures may act as shock absorbers (Buckland-Wright, 1972Rayfield, 2004), absorbing up to 100% more strain energy than bone (Jaslow, 1990) and acting as strain sinks, protecting surrounding bones from damage (Rafferty et al, 2003).…”