BioArt Winner: "Human Enamel"
Entrant: Timothy G. Bromage, PhD, Professor, New York University College of Dentistry
Overview of Research: The mechanical efficacy of a tooth is a function of hierarchy of scale and material properties. Macroscopically, the mechanical loading and maximum stress experienced by a tooth and its surrounding structures depend upon the jaw movements and tooth-tooth contacts that characterize an individual's chewing motions. The stress and strain exhibited by the enamel of teeth vary as a result of highly specific collisions that produce facets on the tooth surface.
Microscopically, the enamel of modern humans and their ancestors varies in ways that are demonstrated to resist the propagation of cracks. To examine this problem, it is necessary to image and observe the orientations of units of enamel structure called “prisms” that course outward from the junction with underlying dentine toward the outer surface of the crown of the tooth. The image presented is of a modern human tooth that has been cut through deep to a first molar cusp whose surface was then polished for imaging by backscattered electron imaging in the scanning electron microscope. We see that the prisms have divergent courses, some prisms coursing longitudinally and wander lengthwise in the plane of the image (lower left to upper right) while others course in and out of the plane of the image and appear semicircular. This heterogeneity provides crack propagating resistance to a tooth, enabling it to withstand the mechanical forces of chewing. Investigations of the enamel biology of modern humans has also allowed researchers to observe that early humans (e.g., 1-3 million years ago) with large robust teeth have more anti-crack propagating heterogeneous enamel than other species of early humans, depending on how hard and tough their diet must have been.
Color was imparted to the image by an image analysis program for measuring prism orientation.
Additional Members of the Research Team:
- Khemet Calnek
- Paola Cerrito
- Bin Hu
- Sasan Rabieh