Nano Silica Improves Bending Properties of Glass Ionomer Cement

Objectives:  Silica filler is added to dental restorative resins on the market to improve their physical properties. In this study, the effects of mixing silica nano particles with glass ionomer restorative cement on bending properties were evaluated. Methods: To examine bending properties of glass ionomer restorative cement (Fuji Ionomer Type II, GC, Japan) containing silica nano particles, specimens made of glass ionomer restorative cement mixed with two different diameter of silanized silica nano particle of 16nm (Aerosil R972, Nippon Aerosil Co., Japan) and 10³ nm (SC4500-SMJ, Admatechs, Japan) were prepared. Glass ionomer cement powder was mixed with these silica nano particles at the four different weight percentage of 0 (for control), 0.5, 1.0 and 2.0 wt% (n=11 for each) before preparing the cement mix. Then the mixed cement was applied into Teflon mold (25 x 2 x 2 mm) to prepare specimens. These specimens were stored in distilled water at 37 °C for 24 hours, and flexural strength were measured using three-point bending method with a 20 mm span at a crosshead speed of 0.5mm/min outlined in ISO 9917-2 (1996). Data were statistically analyzed using One Way Analysis of Variance and Holm-Sidak method. Results:  Flexural strength value of glass ionomer specimens with 1.0 wt% of Aerosil R972 (24.93±2.79 MPa) showed significantly larger value than that of control (20.94 ±2.10 MPa) (p<0.05), while other specimen groups (0.5 wt% of Aerosil R972: 19.69±3.23 MPa, 2.0 wt% of Aerosil R972: 22.94±3.57 MPa, 0.5 wt% of SC4500: 21.94±2.59 MPa, 1.0 wt% of SC4500: 20.10±3.73 MPa, 2.0 wt% of SC4500: 19.85±2.24 MPa) did not show any significant difference from the control group. Conclusions:  It was concluded that silanized silica nano particles could work to increase flexural strength of glass ionomer restorative cement.