PROPERTIES OF HEAT-TREATED COMPOSITES AFTER AGING IN WATER

Objectives. Post-cure heat treatments have been shown to increase the fracture toughness and elastic modulus of composites. The objective of this study was to determine ii the increase remained after the compos ites were aged in water.Methods. The fracture toughness (K-lc), flexur al modulus and flexural strength of four experimental and one commerci al composite (Z-100, 3M Dental Products) were tested alter 1, 7, 30, 6 0 and 180 d of aging in 37 degrees C water. The four experimental comp osites were made with a BisGMA/TEGDMA resin and were characterized as follows. Micro = 38 vol% silane-treated silica, Fine = 65 vol% silane- treated quartz of 1-2 mu m average size, Hybrid = 65 vol% silane treat ed quartz of a mixture of 1-2 mu m average and 8 mu m average size, an d Large = 65 vol% quartz of 8 mu m average size (of which only 75% wer e silane-treated). All specimens were light-cured (normal-cured;Triad II - 80 s). One set of each composite was further heat-cured at 120 de grees C for 10 min (heat-cured). A third set of the Hybrid was heat-cu red with simultaneous light exposure (Elipar, Espe) for the first 3 mi n. Results. By 30 d, normal-cured and heat-cured specimens showed sign ificant (ANOVA/Tukey's test; p less than or equal to 0.05) reductions in fracture toughness (avg. 16% and 22%, respectively), flexural modul us (avg. 11% and 11%, respectively) and flexural strength (avg. 25% an d 29%, respectively). Further aging had little effect. The use of addi tional light-curing during heating did not affect the properties more than heat-curing alone. Significance. The improvements in some of the properties of composites produced by heat-treating are of only short-t erm benefit, and are for the most part negated due to an alteration of the resin matrix as the composite equilibrates with water.