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CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
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SEQUENCE:2
UID:UW-Physics-Event-8062
DTSTART:20221209T163000Z
DTEND:20221210T000000Z
DTSTAMP:20260409T193159Z
LAST-MODIFIED:20221209T154503Z
LOCATION:https://uwmadison.zoom.us/j/92137555326?pwd=bWRTVDlWUDNOUDQrM
 lZzQTQ4emdPZz09
SUMMARY:Physical structure of tooth enamel at the nano- and micro-scal
 es\, revealed by x-ray linear dichroism\, and displayed by polarizatio
 n-dependent imaging contrast mapping\, Thesis Defense\, Cayla Stifler\
 , Physics Graduate Student
DESCRIPTION:Tooth enamel is an extremely tough and wear resistant mate
 rial\, withstanding hundreds of Newtons of force every day during mast
 ication. Enamel’s superior mechanical performance is especially impo
 rtant in animals that have particularly high biting forces or use thei
 r teeth to break hard materials like wood\, nuts\, bone\, and shells. 
 Enamel is hierarchical\, meaning that it has different structures at d
 ifferent scales\, from centimeter to Ångstrom. This hierarchy confers
  toughness and longevity to enamel\, especially the micro- and nanosca
 le structure and crystal orientations. We developed Polarization-depen
 dent Imaging Contrast (PIC) mapping of hydroxyapatite and fluorapatite
  (Ca10(PO4)6(OH)2) and Ca10(PO4)6F2)\, based on a physical effect we d
 iscovered: x-ray linear dichroism in all apatite crystals. With PIC ma
 pping\, we reveal for the first time the complex and diverse crystal o
 rientations in enamel from modern and fossil animals\, with nanoscale 
 resolution. Crystal misorientation of adjacent pixels in PIC maps is c
 onverted to toughness\, producing the first ever toughness maps. Surpr
 isingly\, T. rex\, a dinosaur that had an extremely high biting force 
 (15\,000 N)\, has the least tough enamel of the 30 animals we measured
 . The toughest enamel is the saltwater crocodile\, with the greatest b
 iting force of all living animals (16\,000 N).
URL:https://www.physics.wisc.edu/events/?id=8062
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