New simulations tell the whole tooth
Spectral measurements can be used to indicate
tooth decay and to help developers of dental prostheses approximate tooth color.
When researchers use the radiative transport equation to calculate light propagation
within biological tissue, they usually consider it to be a medium that randomly
scatters light, but it actually tends to have an ordered microscopic structure.
Now scientists have solved the radiative transport equation based on measurements
of dentin using computational algorithms called Monte Carlo simulations that consider
how the tissue’s microstructure scatters light.
To make the measurements, Alwin Kienle and Raimund
Hibst at the Institut für Lasertechnologien in der Medizin und Mebtechnik in
Ulm, Germany, focused a 633-nm unpolarized HeNe laser on cubes of dentin and measured
the transmitted light with a cooled CCD camera. The cubes were in water to prevent
them from drying. The researchers compared their measurements to their simulations.
Scientists directed a laser at various
points in a cube of dentin, and the scattered light was cone-shaped. Reprinted with
permission of Physical Review Letters.
Dentin contains numerous tubules that
bend at one point, and the scientists considered these tubules as straight cylinders
of infinite length. They noted that light directed at a cylinder forms a small cone
around it. As the tubules bend, the cones of scattered photons follow the course
of the tubules. Dentin collagen fibers, which decrease the light transmittance through
the tissue, also were included in their simulations. In all cases, their simulations
matched their measurements.
The investigators would like to model
light propagation in the whole tooth and are examining light propagation in tendons.
They believe that the simulations of the light propagation should be modified for
many biological tissues. “Up to now, it was [mostly] assumed that tissue light-scattering
was random, but many tissue types have an aligned microstructure, which means that
the model that has been used cannot be used,” Kienle said.
Physical Review Letters, July 7, 2006, 018104.
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