Predicting transmitted irradiance through CAD/CAM resin composite crowns in a simulated clinical model

Objective. To predict the clinically relevant transmitted irradiance that is available for luting when a CAD/CAM restoration is inserted. The influence of irradiance, exposure distance, light curing unit (LCU) angulation and direction of polymerization is analyzed when curing through crowns of different thicknesses. Methods. Three modern CAD/CAM resin-based composites (RBCs) were used to produce 45 crown-shaped specimens. The distance between fissure and crown base was set at 1.0, 1.5 and 2.0 mm (n = 5). Transmitted irradiance, while using a violet-blue LCU, was measured with a photo-spectrometer. 180 exposure conditions per specimen were investigated by variation in LCU curing mode, angulation, exposure distance and direction. Data was analyzed using univariate ANOVA followed by Tukey HSD (alpha = 0.05) and comparison of 95% confidence intervals. Results. The CAD/CAM-RBC's decadic absorption coefficient ranges from 0.317 mm(-1) to 0.387 mm(-1) and the reflection correcting factor for crowns ranges from 0.305 to 0.337. Transmitted irradiance decreases significantly with increasing exposure distance and decreasing incident irradiance. For tilt angles greater than 10 degrees, transmitted irradiances are significantly reduced (-11% for 20 degrees, -23% for 30 degrees). Significantly lowest transmitted irradiances were measured for vestibular curing direction (up to -15%). Significance. A calculation model can predict the transmitted irradiance through a CAD/CAM restoration in dependence of restoration thickness and radiant emittance. The practitioner can be supported by this model to adapt material choice of dental restoration and adhesive system to the individual situation. Variation in exposure conditions shows negative effect on the transmission of light and should be limited. (C) 2021 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.