Influence of inhomogeneity of light curing unit on microhardness of resin cements under CAD/CAM blocks

Abstract

1. Objectives The light from light curing units passing through the restoration shows an inhomogeneous distribution. The objective of this study was to determine effects of light inhomogeneity on the polymerization of resin cement under CAD/CAM blocks of different types and thicknesses. 2. Materials and Methods IPS e.max CAD (A3 LT, A3 HT), Celtra Duo (A3 LT), LAVA Ultimate (A3 LT) and Vita Enamic (A3 T) were used. Each block’s thickness was 1.0, 1.5, 2.0 and 4.0 mm. A total of 100 specimens were produced. Variolink N (light-cured) and RelyX U200 (dual-cured) were used as resin cements. Light transmission and beam profile of each block were measured. For microhardness measurement, five points (-4 mm, -2 mm, 0 mm, +2 mm, +4 mm) that coincided with the distance from the center to the periphery of the tip were marked on the specimen’s surface. At each point, microhardness was measured immediately, 24 hours and a week after polymerization. 3. Results The resin cement’s microhardness decreased as the thickness of the CAD/CAM block’s thickness increased. The e.max HT groups showed the highest microhardness and the Vita Enamic groups showed the lowest microhardness (p < 0.05). Resin cements with thickness of 1 mm showed relatively uniform microhardness, whereas those with thickness of 2 mm or more showed inhomogeneous microhardness (p < 0.05). 4. Conclusion Translucency and light transmission differed, showing an inhomogeneous distribution depending on the CAD/CAM block’s thickness and types. And light inhomogeneity affected resin cement’s microhardness.