Aesthetic restorations require dental restorative materials to have optical properties very similar to those of the teeth. A method is developed to this end to determine the optical parameters absorption coefficient µa, scattering coefficient µs, anisotropy factor g, and effective scattering coefficient µ of dental restorative materials. The method includes sample preparation and measurements of transmittance and reflectance in an integrating sphere spectrometer followed by inverse Monte Carlo simulations. Using this method the intrinsic optical parameters are determined for shade B2 of the light-activated composites TPH® Spectrum®, Esthet-X®, and the Ormocer® Definite® in the wavelength range 400 to 700 nm. By using the determined parameters µa, µs, and g together with an appropriate phase function, the reflectance of samples with 1-mm layer thickness and shade B2 could be predicted with a very high degree of accuracy using a forward Monte Carlo simulation. The color perception was calculated from the simulated reflectance according to the CIELAB system. We initiate the compilation of a data pool of optical parameters that in the future will enable calculation models to be used as a basis for optimization of the optical approximation of the natural tooth, and the composition of new materials and their production process.
Acousto-photonic imaging (API) is a new approach in biomedical imaging that combines diffuse imaging by photon density waves (PDW) and light "tagging" inside the tissue by focussed ultrasound. This light "tagging" enables 3D optical imaging with mm resolution in tissue limited only by the geometrical extent of the ultrasound focus and the signal to noise ratio.
We discuss some possible mechanisms of light "tagging" and its dependance of different parameters. We present several phantom measurements which investigate advantages and disadvantages of API against PDW. The main advantage of API is the possibility of real 3D imaging while its biggest disadvantage is the poor light intensity from deeper regions.
The system theory was developed from the combination of the operational calculus of N. Wiener and the transfer theory of K. Kuepfmueller. The system theory is the basic for the optical transfer function. With the introduction of a so- called transfer (or system) function, the question arose how to apply this theory to problems in optical tissue diagnostics.