The evaluation of the surface micro-hardness values in different depth of resin blocks

Objective: Computer-aided design and manufacturing technology has shown great improvement in dentistry since the 1980s. This technology is based on a one-stage restoration using prefabricated blocks. Two main types of materials are used during CAD / CAM indirect restorations: glass-ceramic / ceramic and resin composite. CAD / CAM resin blocks are polymerized under high temperature and pressure. Polymerization depth affects the surface hardness of composite resins. When preparing a restoration, different depth layers of the resin block are used. The aim of this study is to show that adequate polymerization is achieved in each layer of the resin blocks and that the hardness of each layer is the same. Two composite resin block materials and one hybrid resin block material were included in this study. Material and method: The CAD/CAM block materials evaluated in this study were Cerasmart, Lava and Vita Enamic Square specimens (n=5/material) of approximate dimensions 10×10×2 mm blocks were sectioned (5 slices/block) from commercially available CAD-CAM materials using a diamond saw (exakt 300 cl Apparatebau, Norderstedt, Germany) with water cooling. All specimens were abraded followed by 500,1200,2500 grid using SiC abrasive paper (exakt 400 cs Apparatebau, , Norderstedt, Germany). After storage in distilled water at 37 °C for 24 hours the Knoop hardness test was performed using a hardness testing machine (Buehler MMT 3 digital micro hardness tester, Lake Bluff, IL, USA) using a load of 500 gf and a loading time of 10s. Results: The material with the highest hardness number was Vita Enamic block, whereas the lowest numbered group was the Cerasmart. The rank order of surface hardness was as follows: Vita Enamic> Lava Ultimate >Cerasmart. Conclusion: The hardness measurements of the layers of blocks were similar