Hydrolytic degradation and cracks in resin‐modified glass‐ionomer cements

Abstract

Water-absorption affects the basic properties of resin-modified glass-ionomer cements (RMGICs). Fick's law is usually invoked to explain the absorption process. The purpose of this study is to show that the absorption in accordance with the Fickian model cannot be extended to the whole of the specimen, and that microcrack formation is the main degradation mechanism for specimens cured in a closed environment. For this purpose, flat disk-shaped paste specimens 1.5 mm thick (aspect ratio 4), irradiated in closed conditions between two glass slides and stored in water for approximately 20 months, were analyzed periodically gravimetrically and under confocal fluorescence microscopy, with absorbed eosin used as the fluorescent probe. At pH 7.0, the specimen surface (10-20 micrometers in depth) absorbed water rapidly, swelled, and disintegrated in 20-40 days. Long-term storage produced isolated cracks and grains, no progress in the swelling, and a slow weight decrease. A lower pH (pH 3.5) produced a significant increase of the number of microcracks. The decrease in the irradiation time (30 s or less) enhanced the erosion process, producing very broad cracks. It was concluded that the prevalent mechanism of long-term hydrolytic degradation was based on the slow formation of cracks, whereas only in the early stage of storage did absorption occur quickly in accordance with the Fickian diffusion.

Effect of Chemical and Mechanical Degradation on Surface Roughness of Three Glass Ionomers and a Nanofilled Resin Composite

“…The acidic storage medium erodes the surface of conventional GI, for example, and causes hydrolysis and dissolution mainly in the polyalkenoate matrix. [25][26][27] This degradation has a detrimental and irreversible effect on the cement surface. As a clinical consequence, the low environmental pH, in association with toothbrushing abrasion, can result in a loss of contour and increasing surface roughness, which increase the rate of wear and can be responsible for bacterial biofilm and stain accumulation.…”

Bond strength of different bracket bonding materials to the enamel subjected to thermal cycling

“…Furthermore, they stated that water absorption during thermocycling may counterbalance the shrinkage caused by polymerization, thus reducing shrinkage stress, which could lead to bond failure 17. The resin matrix of the composite resin absorbs less water than glass ionomer and is more resistant to hydrolytic degradation for being less hydrophilic and absorbing less water over time 20 . Furthermore, glass ionomer cements feature rapid water imbibition in addition to leaching several components, such as organic molecules, silicate, fluoride, calcium and other ions 8 . However, another factor to be considered is temperature fluctuation, to which the specimens were subjected, as well as the distinct linear thermal expansion coefficients of the materials used.…”

“…Bond strength must be high enough to provide bracket stability throughout the course of orthodontic treatment; although towards the end of treatment, such property may no longer be so important due to lighter forces, considering that the final movements are aimed at leveling the teeth within the dental arch. It should be considered that any material present in the oral cavity for a long period of time may have lost some of its mechanical properties due to imbibition, solubility and fatigue, thus reducing bond strength and introducing the need for further visits to reattach the appliances at this stage 8 . In laboratory tests, thermal cycling is used to simulate the normal aging experienced by materials Bond strength of different bonding materials…”

Twenty-four Hour Flexural and Shear Bond Strengths of Flowable Light-cured Composites: A comparison Analysis Using Weibull Statistics

“…As the filler contents of FCRs were lower than those of CCRs, it thus seemed reasonable that cracks occurred more readily in CCRs than in FCRs. Moreover, besides monomer type, filler content, filler particle size, interparticle spacing, and coupling agent, water influences the strength of restorative materials by affecting the filler-matrix interface 19,23,24) . Nonetheless, with FCRs, water sorption which is accompanied by hygroscopic expansion will help to compensate the effects of polymerization shrinkage.…”