Effect of cyclic loading and environmental aging on the fracture toughness of dental resin composite

Abstract

Objective:The main purpose of this study was (1) to investigate the effects of cyclic loading and environmental aging on three dental resin composites with different filler compositions: a fiber filler, a hybrid filler, and a microfill; and (2) to predict fracture in dental resin composite under mixed-mode loading conditions. Methods: Diametral disk specimens 25 mm in diameter and 2 mm in thickness were used in this study. Two methods were used for generating initial cracks in the specimen. The first method involved machining a 3-mm notch in the center of the disk specimens, and then the notch tips were sharpened with a 0.2-mmdiameter jeweler's saw blade. In the second method for obtaining sharper crack tips, a three-way wedge was forced into a 3.175-mm hole drilled in the center of the specimen, resulting in sharp cracks emanating from the notch tips. Cyclic Tests: The specimens were aged for 4 months in air, water, artificial saliva, and a 50/50 (by volume) mixture of ethanol and water at room temperature in sealed polyethylene containers. Both unaged and aged specimens (5 specimens for each variable) were subjected to cyclic loading at a frequency of 5 Hz with sinusoidal loads cycling for 1, 1000, and 100,000 cycles at a load level ϳ60% of the fracture load for noncycled specimens. Following load cycling, the specimens were tested in compression in a displacement-controlled loading mode at a loading rate of 1.27 mm/min. Results: Test results show that aging in a 50/50 alcohol-water mixture lowered the fracture toughness of dental resin composite, which was further reduced by cyclic loading. Mixed-mode tests: The maximum tensile stress (MTS) criterion was used to predict fracture in dental resin composite under mixed-mode loading conditions. The loads at failure were used as input into a finite element model. After obtaining the stress field in the specimens by the finite element method, the mixed-mode stress intensity factors were calculated using an interaction energy integral method. Results: Good agreement was obtained between the fracture envelope predicted by the MTS criterion and the experimental fracture toughness data. Hence, it can be concluded that it is only necessary to characterize the mode I fracture toughness to fully characterize the mixed-mode behavior of the dental resin composites that were considered in the present study.

Investigation of Mechanical Properties of Modern Dental Composites After Artificial Aging for One Year

“…[4][5]8,16 With regard to this aspect, the findings of this in vitro study indicate that the aging medium has a negligible influence on mechanical performance, such as FS and VH. Generally, aging in aqueous solutions or the oral cavity may contribute to the leaching of composite components, degeneration of the cross-linked resin matrix and fostering hydrolysis of the filler-matrix interfaces.…”

“…Numerous in vitro studies have focused on the mechanical performance of dental composite materials after artificial aging. [3][4][5][6][7] Generally, the artificial aging of dental composites accelerates degradation of the material, [8][9] which causes a significant decrease in mechanical properties. However, the comparability of studies dealing with artificial aging of dental composite materials is rather low, as very different aging conditions and durations have been applied and there is only limited evidence as to how far different aging protocols account for differences in the mechanical performance of a specific material.…”

Factors Involved in Mechanical Fatigue Degradation of Dental Resin Composites

“…In restored teeth subjected to chewing simulation, the degradation of properties in the bulk of the composite, rather than solely surface microcracking, was shown to govern fatigue performance (Pieniak and Niewczas, 2012). Fracture toughness, in turn, has been shown to be minimally affected by cyclic loading when specimens are un-aged or aged in air alone (Ravindranath et al, 2007;Lin and Drummond, 2010), while cyclic loading in water and/or solvents leads to a significant decrease in fracture toughness. The effect of mechanical fatigue is highlighted by the progressive deterioration of K Ic with the number of loading cycles, because the matrix phase is especially vulnerable to repetitive strain challenges.…”

“…In contrast, the authors did not observe a change in cyclic fatigue resistance within this period, indicating that the degradation due to water sorption was limited, or that the specimen was not totally saturated. In other, longer term, experiments in which full saturation of the entire polymer network with water or solvents occurred, the softening of the network, in conjunction with other long-term degradative effects, was shown to cause a reduction in the failure resistance of dental composites (Ravindranath et al, 2007), as evidenced by the polymer network becoming less rigid and more yielding to external loads (Pastila et al, 2007). While some plasticization of the network may help to provide an enhanced plastic zone ahead of crack tips for energy dissipation, the reduced properties of the compromised network facilitate the propagation of cracks at lower energies, negating any beneficial effects.…”

Effect of G-Coat Plus on the mechanical properties of glass-ionomer cements

“…This result is in agreement with the results of several other studies. 16,17 The reduction of hardness in the PAMRC due to ageing could be attributed to many factors, including water sorption by the resin component causing plasticization. Since hardness is a surface property, it is affected by water sorption.…”