Remaining unreacted methacrylate groups in resin-based composite with respect to sample preparation and storing conditions using micro-Raman spectroscopy.

The aim of this study was to measure degree of conversion (DC) of resin-based composites (RBCs) using micro-Raman spectroscopy followed by different sample preparation procedures and storing conditions. Ninety samples of Tetric EvoCeram (Ivoclar Vivadent, Schaan, Liechtenstein) were prepared in standardized molds and cured with a high powered LED light-curing unit, bluephase (Ivoclar Vivadent, Schaan, Liechtenstein) for 20 s. Samples were allocated to eight groups. DC of groups 1 and 2 was recorded without or after polishing. DC in groups 3 and 4 was recorded from vertically sectioned samples versus "split" samples. DC in groups 5-8 was recorded after storing samples at room temperature and humidity, in 90 +/- 2% humidity at 37 +/- 1 degrees C, distilled water at 37 +/- 1 degrees C or buffered incubation medium (BIM) at 37 +/- 1 degrees C for 24 h. Mean values of DC in polished and unpolished samples were 63.6% (+/-3.2%) and 54.7% (+/-5.2%), respectively (p < 0.0001). There was no significant difference in DC after sample-sectioning (p > 0.05). Significantly higher DC values were obtained after storing samples in BIM (76.8% +/- 2.1%) than in distilled water (59.7% +/- 5.7%), extreme humidity (60.3% +/- 3.9%) or in room conditions (63.6% +/- 3.2%) (p < 0.001). DC of an RBC measured by micro-Raman spectroscopy may be affected by differences in sample preparation and storing conditions, making it difficult to extrapolate data from in vitro studies into clinically relevant information.