Fracture properties of aged and post-processed dental composites

The purpose of this study was to determine the flexure strength (sigma(f)), Young's modulus (E), and fracture toughness (K-IC) of five dental composites after aging in water and air. The composites were, by weight, 75% or 79% glass filler and 25% or 21% resin composed of 60% Bis-GMA and 40% TEG-DMA. The filler was either strontium glass (75Sr or 79Sr) or a combination, by weight, of 90% strontium glass and 10% colloidal silica (75Sr10 or 79Sr10). The specimens, 2 x 4 x 70 mm bars, were aged in either air or distilled water at 37 degrees C and were tested in their respective aging media at a loading rate of 1.22 mm/s. The sigma(f) and E were rested in four-point loading and the K-IC in three-point loading. The addition of the fillers to the unfilled resin resulted in a statistically significant increase in the flexure strength, flexure modulus, and fracture toughness. Aging in air had minimal effect on these properties. However, testing and aging in water led to a significant decrease in the mechanical properties in the first 6 months, bur had limited effect from 6 to 12 months.