Mammals are diphyodonts, and therefore they successfully grow only 2 sets of teeth during lifetime (with the exception of continuously-growing incisors of rodents and lagomorphs). Therefore, mammalian teeth must function for many years under repeated daily loading without failing [1]. Yet most vertebrates exhibit polyphyodonty, where tooth “replacement” or “regeneration” allow recovery from damage or loss, thus ensuring survival without the need for dental care. The Atlantic wolfish (Anarhichas lupus) is such an animal: as a teleost, it has teeth that are highly adapted to crushing hard-shelled organisms that make up its diet. The dentin type of wolfish teeth is osteodentin, which is radically different in structure from the dentin of most vertebrates, containing large-diameter (20+ micron) sized canals. Thus, this dentin type is presumably well adapted to their diet and the significant mechanical challenges it presents. Here, using extracted teeth and tomographic imaging, we study in-situ the deformation response of the tooth structures.

Our work quantifies the mechanical performance of whole wolfish teeth loaded to simulate mastication. In-situ compression loading experiments in combination with high-energy phase contrast enhanced tomographic imaging in the synchrotron, made it possible to utilize digital volume correlation (DVC) to reveal 3D deformation patterns. We find that axial loading of these teeth comprising osteodentin yields inwards compactification resulting in a structural negative Poisson’s ratio (a phenomenon known as Auxeticity). Our work provides insights into structure-function relationships of an evolutionarily optimized replaceable whole tooth design, where it is likely that the simultaneous inward deformation along X Y and Z directions is a useful approach for energy conservation for efficient ingestion.

[1] P. Zaslansky Relations Between Shape, Materials Properties, and Function in Biological Materials Using Laser Speckle Interferometry: In situ Tooth Deformation Adv. Funct. Mater, 2006, 16, 1925-1936.