IN-VITRO AGING OF DENTAL COMPOSITES IN WATER - EFFECT OF DEGREE OF CONVERSION, FILLER VOLUME, AND FILLER MATRIX COUPLING/

The purpose of this study was to evaluate the long-term effect of agin g in water on the physical properties of experimental composites havin g systematically controlled differences in degree of conversion (DC), filler volume fraction (V-f), and percentage of silane-treated fillers . Composites were made with a 50% Bis-GMA:50% TEGDMA light-cured resin and a 1-2 mu m (average size) strontium glass filler (+ 5 wt% SiO2 mi crofiller). For composites A-E, the DC was varied from 56-66% by chang ing the curing time; for D and F-I, the V-f was varied from 28-62 vol% ; and for D and J-M, the percent of fillers with a silane coupling age nt (gamma-MPS) was varied from 20-100%. Fracture toughness (K-Ic), fle xure strength (FS), elastic modulus (E), and hardness (KHN) were teste d after soaking in water at 37 degrees C for 1 day, 6 months, 1 year, and 2 years. The K-Ic was reduced 20-30% for all composites after 6 mo nths, with minimal changes thereafter. The FS was reduced for several composites at 6 months, but only those with poor cure (A and B) were l ower at 2 years than they were initially. The E was not reduced for mo st composites. Hardness was reduced for most composites after 6 months , but many returned to their original levels at 2 years. Long-term agi ng in water caused a reduction in the K-Ic, independent of composition , but had little effect on other properties, suggesting limited degrad ation of composites in water. (C) 1998 John Wiley & Sons, Inc.