Solvent Degradation and Reduced Fracture Toughness in Aged Composites

Abstract

Qartz- and barium-glass-filled composites aged for more than one year in ethanol experienced a significant reduction in fracture toughness (K1c), essentially identical to that experienced after two months of aging. This reduction is mainly attributed to a softening of the resin matrix, but cracking within the resin and at the filler/matrix interface, as revealed by SEM microscopy, may also have contributed. No significant cracking could be seen in the composites aged in water. Composites post-cured at temperatures approaching their glass-transition temperature also experienced a reduction in K1c after alcohol storage. Storage in water for one year had little effect on the K1c of composites cured at oral temperatures, but a significant increase was observed for those post-cured at elevated temperatures. This increase is difficult to explain, but appears to involve a filler/matrix interfacial phenomenon, because it was not observed in the unfilled resin. The results of this study demonstrate that an alteration in the fracture resistance and some degradation of the filler/matrix interface, as has been observed clinically, occur after long-term exposure of dental composites to certain solvents used as food-simulating liquids.

Surface and bulk properties of dental resin- composites after solvent storage

“…Organic solvents, as Ethanol and MEK, showed more detrimental effect on the mechanical properties compared to water storage. Several studies have demonstrated more complete extraction of monomers and oligomers with the organic solvents that could explain their stronger impact on the mechanical properties [8,12,45,[47][48][49][50].…”

“…From a material aspect, the performance of the resincomposite restoration depends on several factors including the monomer system, the filler type, filler loading and the extent of cure [7]. Degradation of resin-composite restorations in the oral environment can be simulated by the use of different food simulating solvents which are known to cause different effects on the mechanical properties of the restoration and its longevity [4,[8][9][10]. Similar polarity of a particular solvent and a substance will tend to make them mutually soluble, different polarity on the other hand will make the solubility difficult [11,12].…”

Sorption and solubility of luting cements in different solutions

“…However, the opposite was found for resin-based cements. This might be due to the enhanced ability of ethanol to penetrate and swell the crosslinked polymer network in comparison to water 29) . The uptake of water or solvent by a resin-based matrix may cause swelling, and a reduction of interchain interactions that may soften the resin 27) .…”

“…Many mouthrinses include ethanol in their composition, and ethanol may accelerate the hydrolytic degradation of resin-based materials 28) . On this ground, subsurface and surface degradation of resin composites can be reproduced in the laboratory by storage in 50:50 ethanol:water solution 29,30) , which is listed as a food-simulating liquid in the U.S. Food and Drug Administration (FDA) Guidelines. The purpose of this study was to measure the solubility, sorption, and dimensional change of eight luting cements (six resin-based and two resinmodified glass ionomer cements) in two different solutions: 50％ ethanol:water and distilled water.…”

Flexural Performance of Flowable versus Conventional Light-cured Composite Resins in a Long-term in vitro Study

“…The degradation of composite resins in the oral environment is considered to be attributed to the resin matrix, filler particles, and hydrolytic instability of silane coupling agent at the polymer-silica interface [28][29][30][31][32][33][34][35] . After one-year water storage in the present study, all composites showed higher flexural strengths in comparison with their immediate values.…”