Effect of Curing Process of Dental Nanocomposite Resin on Shore Hardness

The objectives of this study is to determine the effect of light curing modes and curing times on the Shore hardness of hybrid composite resin filled with titanium dioxide (TiO2) nanoparticle. The materials used were hybrid composite resin and titanium dioxide nanoparticles (TiO2 nanoparticles). Four groups of composite resin specimens were prepared; one as received and three groups reinforced with TiO2 nanoparticles in concentrations of 0.1, 0.2 and 0.3 wt. %. TiO2 nanoparticles were manually mixed with hybrid composites resin. The resulting paste was packed into plastic bars. The specimens were then polymerized from both sides for 10, 20, 40, 60 and 80 seconds using a visible light curing unit. The light polymerization modes used were gradually strong, flashing and strong mode. Surface hardness was measured using Shore D durometer test. The use of gradually strong curing mode resulted in lower hardness for the unreinforced hybrid composites resin filled with TiO2 nanoparticles compared with the hardness obtained using the flashing mode and strong curing mode. Specimens of curing time 10, 20 and 40 seconds exhibited lower hardness compared to 60 and 80 seconds curing time. This study indicated that, strong curing mode produced dental nanocomposite resin with higher Shore hardness, where 80 seconds curing time gave higher values of Shore hardness. Shore hardness results are significantly affected by curing times compared to curing modes.