Impact of cerium oxide nanoparticles incorporation on shear bond strength and surface hardness of acrylic-based soft lining material

Background and Aim: Soft liners are designed to modify the surfaces of prostheses that interact with the mouth’s soft tissues to improve denture performance. One method of improving its mechanical properties involved the application of nanotechnology. This work aimed to determine impact of cerium oxide nanoparticles (CeO2NPs) on acrylic-based soft liner’s surface hardness and shear bond strength. Materials and Methods: CeO2NPs were added to soft liner monomer with weight percentages of 0%, 2%, and 3%. Sixty samples were prepared for shear bond test and surface hardness test with 30 samples each. Shear bond samples were prepared by constructing two acrylic blocks which assembled over each other creating a square space in the middle with dimensions around 25 mm in length and width and 3 mm in depth for the addition of soft liner material. The surface hardness samples were constructed as a disc with diameter of 35 mm and 6 mm thickness. Instron testing machine with a load of 50 KN and cross-head speed 0.5 mm/min was used for testing the shear bond strength, while surface hardness was tested by Shore A durometer. The morphological features of soft liner samples before and after the addition of CeO2NPs were examined by scanning electron microscopy (SEM). The data were analyzed for normality and homogeneity by Shapiro-Wilk test and for significance by ANOVA and Tukey’s multiple comparisons tests using SPSS version 21 software. Results: Soft liner samples demonstrated a significant increase in shear bond strength from 11.6 ± 1.51 MPa for the control group to 16.1 ± 1.37 MPa and 18.9 ± 1.29 MPa for 2%wt. and 3%wt. CeO2NPs treated groups, respectively. The surface hardness value of the samples with the addition of 3%wt. CeO2NPs increased significantly to 61.01 ± 0.98 Shore A in comparison to the control group 59.47 ± 0.97. However, the 2%wt. CeO2NPs-treated group exhibited no significant difference with the rest groups. SEM showed that after CeO2NP incorporation, the nanoparticles were homogenously distributed on the sample surface leading to a decrease in surface porosity. Conclusion: The addition of 2%wt. CeO2NPs improved the shear bond strength of the soft lining material with a non-significant effect on surface hardness. This shows the efficacy of CeO2 in improving some material mechanical properties.