Optical Properties of Resin Composites through Optical Coherence Tomography

Objectives: Optical phenomena are important to understand light transmission through resin composite layers. The extent of the light penetration to start the polymerization depends on the absorption coefficients of the resin composite's components. The objective of this study was to investigate the optical properties of dental composites through Optical Coherence Tomography (OCT), a non-invasive technique that uses the properties of coherence of light to form images. Methods: Four types of dental composite resins were analyzed with OCT: a microparticulate composite, Durafill (Heraeus Kulzer Weihrheim, Germany); a microhybrid composite, Filtek Z 250 (3M ESPE St Paul, MN, EUA); a nanofiller composite, Filtek Z 350 (3M ESPE, St Paul, MN, EUA); and the monomer matrix BisGMA:TEGDMA:UDMA 40:40:20 without fillers. Stainless steel matrixes (internal diameter=8 mm and height =0.65 mm) filled with the resin composites were placed between two microscope glass slides. All samples were cured with Led light source (Radiical SDI) for 60 seconds and were positioned on OCT sample support. A commercially available OCT system (SR-OCT: OCP930SR/Thorlabs) with 930 nm central wavelength was used. Images were evaluated using ImageJ and A-scans were analyzed using the Origin 8.0 program, after a filter treatment using Matlab. Results: The commercial composite resins showed different attenuation coefficients: -4,8 mm-1; -3,2 mm-1 and -2.9 mm-1 for microparticuleted, nanofilled and microhybrid composites. The monomer matrix, without filler, had the lowest attenuation coefficient -5.3 mm-1. Conclusions: Attenuation coefficient of light is different for composites with different size of particles. The optical coherence tomography was able to quantitatively measure the attenuation of light of dental resin composites and further studies with different resin composites should be done to assess the optical characteristics of these materials.