Dynamic monitoring of refractive index change through photoactive resins

ObjectivesThe change in optical characteristics through the bulk of curing photopolymers is not fully understood. Photopolymerization processes are accompanied by photoinitiator absorption, density changes and volumetric shrinkage, which alter optical properties and affects curing efficiency through depth.MethodsThis investigation demonstrates the use of a novel low coherence interferometry technique for simultaneous measurement of optical (refractive index) and physical (shrinkage) properties throughout curing of photoactive monomers containing various concentrations of bisphenol-A-diglycidyl ether dimethacrylate and triethylene glycol dimethacrylate.ResultsReliability of the interferometry technique was compared with an Abbé refractometer and showed a significant linear regression relationship (p < 0.001; adjusted R2 > 0.99) for both uncured and cured resins. The extent and rate of refractive index change and magnitude of shrinkage strain was dependent upon monomer formulation.SignificanceThe development of this interferometry technique provides a powerful non-invasive tool that will be useful for improving light transmission through photoactive resins and filled resin composites by precise control of optical properties through material bulk.