Effects of resin formulation and nanofiller surface treatment on the properties of experimental hybrid resin composite.

This study evaluated the effects of nanofiller surface treatment and resin viscosity on the early and long-term properties of experimental hybrid composites. Three resin formulations (low, medium and high viscosity) were prepared by varying the ratio of TEGDMA:UDMA:bis-GMA (47:33:16 wt%; 30:33:33 wt%; 12:33:51 wt%). Composites contained 71.3 wt% silanated strontium glass (1-3 microm) and 12.6 wt% of either silanated or unsilanated silica (OX-50; 0.04 microm). Specimens (n=10) for flexural strength, flexural modulus, fracture toughness and Knoop hardness were tested after 24 h, 1 and 6 months exposure to water at 37 degrees C. Degree of conversion (DC) was determined 24 h after photoinitiation using FTIR. Resin viscosity only had a marginal influence on the mechanical response of composites but it can be adjusted to achieve a balance between DC and mechanical properties. Adding non-bonded nanofiller to hybrid composites had no systematic effect on DC. Non-bonded nanofillers had no significant effect on the long-term properties of hybrid composites.