Optical and thermal depth profile reconstructions of inhomogeneous photopolymerization in dental resins using photothermal waves
Journal of Applied Physics
Temperature stability of Bloch surface wave biosensors Appl. Phys. Lett. 99, 231107 (2011) Making human enamel and dentin surfaces superwetting for enhanced adhesion Appl. Phys. Lett. 99, 193703 (2011) Processing weak electrical signals with threshold-potential nanostructures showing a high variability Appl. Phys. Lett. 99, 153703 (2011) Biophysical attributes of an in vitro spinal cord surrogate for use in developing an intradural neuromodulation system J. Appl. Phys. 110, 074701 (2011) Use of
... 74701 (2011) Use of an AC electric field in galvanotactic on/off switching of the motion of a microstructure blotted by Serratia marcescens Appl. Phys. Lett. 99, 063702 (2011) Additional information on J. Appl. Phys. Photopolymerization is a process that depends, among other factors, on the optical properties of polymerized materials. In turn, this process affects longitudinal light transport in these materials, thereby altering their optical absorption coefficient which is thus expected to exhibit depth dependence. Furthermore, polymerization affects the thermal properties of these materials. A robust theoretical approach to the study of the depth-dependent optical absorption coefficient, ␤͑x͒, and thermal diffusivity, ␣͑x͒, in materials exhibiting depth profiles of these parameters has been developed through the photothermal inverse problem based on the concept of the thermal-harmonic oscillator. Using this concept in the frequency-domain nonhomogeneous photothermal-wave boundary-value problem, the simultaneous reconstruction of arbitrary simultaneous optical and thermal depth profiles was achieved using a multiparameter fitting method to the experimental amplitude and phase. As a first application of the theory to partially polymerized Alert Composite ͑shade A3͒ dental resin, with curing induced by a blue light-emitting diode, the ␤͑x͒ and ␣͑x͒ depth profiles were reconstructed from photothermal radiometric frequency-scanned data. A strong anticorrelation of these two depth profiles was observed and was interpreted in terms of photochemical processes occurring during the optical ͑photocuring͒ creation of long polymeric chains in the resin. The photothermally reconstructed depth profiles may have implications for the optimization of blue light curing methods using such resins in dental clinical practice.