Mechanical and hydrolytic degradation of an Ormocer®-based Bis-GMA-free resin composite

Abstract

The aim of the study was to evaluate the mechanical stability of bisphenol A-glycidyl methacrylate (Bis-GMA) and Ormocer-based resin composites before and after water absorption and to examine water saturation. Disc-shaped specimens of the Bis-GMA (Grandio SO, Voco) and the Ormocer-based (Admira Fusion, Voco) dental resin composites were produced, stored in water, and weighed after pre-determinedtimes to measure the absorbed water. Bend bars were produced and stored for 24h in dry conditions as well as in distilled water for 14days or 60days at 37°C. The initial flexural strength (FS) under quasi-static loading and flexural fatigue strength (FFS) under cyclic loading were determined under 4-point bending.Fracture toughness (KIc) of both composites was measured using the single-edge-V-notch-beam (SEVNB) technique after the same storage conditions under 3-point bending. Within the first 14days, storage conditions did not affect the initial FS of Grandio SO, while a significant drop in initial FS was observed for Admira Fusion after 2weeks in water and most of the water was absorbed within this time. FFS for the Bis-GMA composite was not reduced before 2months in water, whereas for the Ormocer®-based composite, there has been a significant decrease in strength after cyclic fatigue already at 2weeks of water storage. KIcof Admira Fusion decreased significantly after both storage periods, while KIcof Grandio SO decreased only significantly after 2weeks of water storage. All mechanical properties of the Bis-GMA composite were superior to those of the Ormocer®-based material, except water sorption. Water storage seems to have a much more pronounced effect on the mechanical properties of Ormocer®-based dental composites in comparison to Bis-GMA-based composites.