Development of novel dental nanocomposites reinforced with polyhedral oligomeric silsesquioxane (POSS)

Objectives: It has been the focus to develop low shrinkage dental composite resins in recent ten years. A major difficulty in developing low shrinkage dental materials is that their deficiency in mechanical properties cannot satisfy the clinical purpose. The aim of this study is to develop novel dental nanocomposites incorporated with polyhedral oligomeric silsesquioxane (POSS). It is especially interesting to evaluate the volumetric shrinkage and mechanical properties, improve the shrinkage, working performances and service life of dental composite resins. Methods: The effect of added POSS on the composites' mechanical properties has been evaluated. The weight percentages of added POSS are 0, 2, 5, 10 and 15 wt% respectively. Fourier-transform infra-red spectroscopy and X-ray diffraction were used to characterize their microstructures. Physico-mechanical properties that were investigated included volumetric shrinkage, flexural strength, flexural modulus, compressive strength, compressive modulus, Viker's hardness and fracture energy. Furthermore, the possible reinforced mechanism has been discussed. Results: The shrinkage of novel nanocomposites decreased from 3.53% to 2.18%. The nanocomposites incorporated with POSS showed greatly improved mechanical properties, for example, with only 2 wt% POSS added, the nanocompsite's flexural strength increased 15%, compressive strength increased 12%, hardness increased 15% and uncommonly, even the toughness of resins was obviously increased. With 5 wt% POSS polymerized, compressive strength increased from 192 MPa to 251 MPa and compressive modulus increased from 3.93 GPa to 6.62 GPa, but flexure strength began to decline from 87 MPa to 75 MPa. This finding indicated that the reinforcing mechanism of flexure state maybe different from that of compressive state. Conclusions: The mechanical properties and volumetric shrinkage of dental composite resins polymerized with POSS can be improved significantly. In current study, the nanocomposite with 2 wt% POSS incorporated is observed to achieve the best improved effects.