Brown University School of Engineering

IMNI Distinguished Lecture by Dr. Brian Lawn: Inferring Biological Evolution from Fracture Patterns in Teeth

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Monday, November 18, 2013 4:00pm - 5:00pm

"Inferring Biological Evolution from Fracture Patterns in Teeth" Dr. Brian Lawn, National Institute of Standards and Technology Monday, November 18 4:00 pm - 5:00 pm 3:30 pm Reception Barus & Holley 190 Teeth are critical markers of our present and past, how we eat, how we evolved. They are relatively hard and brittle with a complex microstructure, and are thereby of considerable interest to biomaterials scientists. It is hypothesised that specific tooth forms are adapted to resist fracture, in order to accommodate the high bite forces needed to secure, break down and consume food. Three distinct modes of tooth fracture are identified: longitudinal fracture, where cracks run vertically between the occlusal contact and the crown margin (or vice versa) within the enamel side wall; chipping fracture, where cracks run from near the edge of the occlusal surface to form a spall in the enamel at the side wall; and transverse fracture, where a crack runs horizontally through the entire section of the tooth to break off a fragment and expose the inner pulp. Simple, explicit equations are presented expressing critical bite force for each fracture mode in terms of characteristic tooth dimensions. Distinctive transitions between modes occur depending on tooth form and size, and loading location and orientation. Attention is focused on the relatively flat, low-crowned molars of omnivorous mammals, including humans and other hominins, and the elongate canines of living carnivores. Allusion to the conical dentition of reptiles and the columnar teeth of herbivores is also made, to highlight the generality of the methodology. How these considerations impact on dietary behaviour in fossil and living species is considered. Brian Lawn gained B.Sc. and Ph.D. degrees in Physics at the University of Western Australia in 1959 and 1963, respectively. After graduating, he spent four years as a Postdoctoral Fellow in the School of Physics at the University of Bristol and the Department of Engineering and Materials Science at Brown University. From 1968 to 1981 Dr. Lawn was a professor in Physics at the University of New South Wales. In 1981 Dr. Lawn joined the National Institute of Standards and Technology, and in 1987 was appointed to the position of NIST Fellow. He has held Adjunct Professor appointments at several universities worldwide. Dr. Lawn is the author of the text "Fracture of Brittle Solids", first published in 1975 and now in its second edition. He has published over 300 research papers, with an h-index of 67. In 2001 he was elected to the U.S. National Academy of Engineering, and in 2012 to the Australian Academy of Science. He was awarded an Honorary Doctorate in Engineering by the University of Western Australia in 2008.