Determination of dental composites properties by using a fizeau fiber interferometer

Abstract

Several interferometric techniques based in fiber optics components have been developed in the last twenty years. Most of these systems are simple and compact compared with similar bulk design. However, fiber presents some particular characteristics as polarization fluctuations which can limit the system performance. Because its design, the Fizeau fiber interferometer is intrinsically free of this problem. Resolution of some manometers has been achieved by this method. Employment of fiber optic guiding limits the effect of external perturbation and makes the development of a compact analysis device possible. In this work, we use a simple Fizeau fiber interferometer to measure polymerization shrinkage and the thermal expansion coefficient of polymer composites. These parameter are particularly important for the development of new dental materials because the reduction of composite shrinkage presents an important goal in biomaterials research. The possibility of using interferometry to measure linear shrinkage in light-cured dental resins was assessed by testing experimental photocured resins based on Bis-GMA-TEGDMA. The instrument enables quantitative measurements providing data for the continuous shrinkage evolution during photopolymerization. The present study has been conducted to gain a further insight into the volumetric changes which occur during photopolymerization under nonisothermal conditions. As example of the technique goodness, the percent linear shrinkage of composite used in dentistry applications were measured as a function of the illumination irradiation and sample thickness. Results were in agreement with previously published results. On the other hand, the vitrification process was also monitored by using the interferometer together with a vibrating cantilever in order to follows the amplitude changes of the oscillations when the material solidifies. Results also shows that the resins vitrified very rapidly compared with the volume or the thermal relaxation.